.- r . Msaumecaoss..a;- v, . H . , ‘ ’ " ' u-« -r_.,. ,m —-¢.-,rr.. H . , ‘ , ' . . ' . ‘ . V . . v nvn/xn‘ru- wrrw mu”.- , ”w. ...,.,. ”if, M. . . . WM» nan-“(.4)“ .rln'pl’f‘npr'h‘r' p,»rr,.-rrrz.arfl —vvvrk a», Vll"yhurrr/I ‘..r.,..,./.,- -,... -,-. 4. .. ...«- r. .1, aw .. V — .,.,..,, .1. m , _. .«. . - ,w- ->~/—v‘r r.» v ,...,. (r; w- rv-r-rr-ar-vrcuvm «a, 4~ .,,.. ,H. , . ,., ”w. , ,,.. ,. a“ .7. aru-l-n-r’f’l‘FF1fl my rrp-aruwrrw r- ’v’nruufir- .,., . .. . u 7-, .1 . . . ,Mnmmr... fyn'rf'rry.rtl r... ... rry.r.'- q. WM...” ,_ .«v- 0.. F,n—i>l-~rrv_ , uvy'--rr‘ 'r'vv‘t‘r‘r'rlv‘v— rvr'vr w IK-rr-d .y ._ ~ ,- .— r! rv—r'v .«.- -r-r—vw - y. -~‘>\"r v-r- "M-ww re—r 1:».— "~- v»- -r,- —p-Irrr' sy-ovt'y—‘sv-J’ —.n..,. argumen‘prfl , ,,,., .4...” fi-n-rr— 1. F. Imp->9" —....._. anrrw n-‘ph,,. . ¢ . rm.--” 4.-. Fr.--'4)r"l ind-">1" ~rr—~o.wvr ~‘I‘vrflrvtv-fl'rv1‘v; 9-,... ,.,,‘ V. . V , “-7 a". ..,,, «Wu .1 ~-»p,~r.w.u-r-—u~ vs-rr..--~Tr-n~~- r~ w P w -- ,, w w- .«... .- Mann-hp w‘n-l.v'»-r, , ‘ ”a..-” munw 'Hvl'wh\‘vorrv-uv~‘th ‘NO‘Iflr-t—(u‘np'r’lv-pryr'v? w¢,--~’~w‘V—J'vvl-Iya-vuryhp, .. . .. ‘ '3‘ v». H . ‘ ‘ . ‘ ' . , . .. . ‘ ,, H. .. ‘ .‘ V .. . .w.’ . _ y. , .,., .. . _ V . "WM. ,M." , .'.,vyly¢-yfi. f‘ , .,., u m- 902 of the total y—ray intensity) have been incorpo— rated in a decay scheme having 31 levels with energies of 0, 899.2, 1273.9, 1562.8, 1817.3, 2065.1, 2185.4, 2257.9, 2385.8, 2434.0, 2480.0, 2506.8, 2919.5, 2928.5, 3029.0, 3092.0, 3104.9, 3170.0, 3215.0, 3232.0, 3637.8, 3768.4, 3782.0, 3814.4, 3826.2, 3842.2, 3875.7, 3996.1, 4080.5, 4165.5, and 4249.6 keV. A secondary decay scheme was proposed; y—ray transitions in this decay scheme are placed solely on the basis of Precise energy sums and weak coincidence data. One hundred and forty— sum) 1 ran have been mt 11.7-hour 312“. 1 my: (accounting for >801 Mat0,126.4, 186.4, I 31.6,1641.6, 1802.4, 203: m, 2143.7, 2753.4, 279 “Wary decay scheme v1 533%? 51m and weak cci Units on the 3; gm“ investigated are :ac James Burke Cross seven (147) y rays have been associated with the electron capture decay of 11.7—hour Bi203. Twenty-six (26) levels accommodating 51 y rays (accounting for >807. of the total y—ray intensity) have been placed at 0, 126.4, 186.4, 820.2, 825.2, 866.5, 896.9, 1033.6, 1160.8, 1547.6, 1641.6, 1802.4, 2033.8, 2184.0, 2387.8, 2568.9, 2620.5, 2667.8, 2713.4, 2748.7, 2753.4, 2793.7, 2821.1, 2964.4, 3016.9, and 3045.2 Rev. A secondary decay scheme with transitions placed solely on the basis of energy sums and weak coincidence data was also proposed. Limits on the spin and parity assignments of the nuclear states investigated are made on the basis of log ft values, relative Y intensities to states of known spin and parity, and transition multi- polarities (for those transitions where internal conversion—electron intensities were available). A brief survey of and comparison with previously reported scattering reaction data is presented for Pb203 and szo”. Nuclear shell—model level spacings in the Vicinity of Z=82 and 1V=121 are discussed. Possible shell—model transitions associated with the 33204 electron capture decay of 3120 are suggested. Probable dominant configurations of 8 low—lying levels in Pb203 are offered in simple shell- and collective-model terminology. Finally, a summary of the previous theoretical calculations on szo1+ is made along with sug— gestions for a theoretical re-evaluation of these lead isotopes. m m u m \(' in partial a mu: DECAY scamms OF 31203 AND 312°” . By James Burke Cross A THESIS Submitted to Michigan State University [in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSPHY Department of Chemistry 1970 (z 5 . 6\\ l " I earnestly posing this area of S curagenent, and pati thesis preparation at harm and enthusia :ave become overwhelm ACKNOWLEDGEMENTS I earnestly wish to thank Dr. Wm. C. McHarris for pro— posing this area of study. In addition, his expert guidance, en- couragement, and patience during the experimental work and in the thesis preparation are greatly appreciated. Without his constant interest and enthusiasm the sheer magnitude of the project might have become overwhelming. Working in close cooperation with our group,Dr. W. H. Kelly, Physics Department, must receive my heartfelt thanks. His invaluable help on several computer programs relieved me of a great deal of drudgery connected with relatively routine calculations. Dr. H. G. Blosser, Mr. H. Hilbert, and Dr. W. P. Johnson assisted with the maintainance and operation of the Michigan State University Sector-Focused Cyclotron which was used to prepare the radioactive sources for this investigation. Dr. D. B. Beery, Mr. J. Black, Mr. w. B. Chaffee, Mr. R. E. Doebler, Mr. R. E. Eppley, Mr. G. C. Geisler, Mr. R. Goles, Mr. K. Kosanke, and Mr. R. Todd have provided stimulating discussions and advice throughout the data acquisition and analysis. Mr. and Mrs. w. Merritt, Miss T. Arnette,and the Michigan State cyclotron computer staff have also aided greatly in the data acquisition and evaluation through the use of the XDS Sigma-7 Cyclotron Computer. I also want to thank the Department of Physics for the ii :zfizgmgeratio: they hav‘ inland financial aid this mini. Our secretary Hrs. 1. I thank the 15.8. Amy who tmplete this degree. iatknouledge thv fir Ltehnndatinn, L'.S. A1321 =17: Timmy . Finally, I thank :y 31:?" ' . Non, perspiration. am *3 5min. ' ' t their oumtmuflng cooperation they have extended to me. Withou ' been Nwsical and financial aid this progect could never have successful. thesis. Our secretary Mrs. I. Samra typed portions of this I thank the U.S. Army for allowing me to return to sdmol U)complete this degree. ' al I acknowledge the financial assistance of the Nation d Michigan Seimme Foundation, U.S. Atomic Energy Commission, an State University. t, Finally, I thank my wife Karen for her encouragemen ' course of hmpiration, perspiration, and understanding during the this study. iii WLE 0‘ Han? Hm. I I IIII O 0 ..... 'zgnr l. MODUCUOS ........ 1.1. General Survey 1.2. Lead Level Sci 1.2.1. Pb'f’ 1.2.2. Phi?” 1.2.3. 91,3?" 1.2.4. 91,31 1.2,5_ phi: 1.2. 1.2 TABLE OF CONTENTS Page ACKNOWLEDGEMENTS . . . . . . . . . . . 11 LIST OF TABLES.".."'IOOOOCooo-uoooooo.OoooooooocoolooluooIOI xii xiv LIST OF FIGURES...... Chapter IODOOO‘IOOIOCOIO I. INTRODUCTION................. .... . at... 1~1. General Survey of Pb Isotope Systematics.. clot-Igloo 1.2. Lead Level Schemes................. Oolooo‘ 1.2.1. Pb208 Level Scheme........ ...... 9 con...- 1.2.2. Pb207 Level Scheme. ....... . ..... 9 .0000... 1.2.3. Pb206 Level Scheme ....... ..... 12 0000.... 1.2.4. Pb205 Level Scheme............. 15 OIOOQOIIO 1.2.5. PbZOL+ Level Scheme............ 16 l.2.5.A. szoum Isomeric Decay..... 1.2.5.B. Electron Capture of BiZO”.... 17 23 1.2.6. Pb203 Level Scheme............ 24 1.2.6.A. Pb203 Decay Scheme........ 1.2.6.3. Pb203m Decay ......... ........ 24 25 l.2.6.C. Bi203 Decay Scheme........... II. EXPERIMENTAL APPARATUS AND TECHNIQUES................ 31 2-1- Source Preparation............................. 32 ... 32 OccuoooOOIOltl 2.1.1. Tl Targets............ 34 Innocent-0.0... 2.1.2. Pb Targets ..... ......... 39 coco-o. 2.2. The Gamma—Ray Spectrometer...... 39 2.2.1. Singles Experiments...... iv 2.2.2. (Joint 2.2.1 2.2. 2.3. Data Analysi 2.3.1. Cam 2.3. 2.3 2.1. III. Chapter 2.3. 2.4. 3.1. Page 2.2.2. Coincidence Experiments................ 39 2.2.2.A. NaI(T1) Split Annulus — Ge(Li) Spectrometer................. 40 2.2.2.B. Multiparameter Ge(Li)-Ge(Li) Spectrometer................. 41 Data Analysis.. ....... ......................... 45 2.3.1. Gamma Energy and Intensity Measurements 45 2.3.1.A. SAMPO Spectrum Analysis Rou- tine............. ..... ....... 45 2.3.1.B. MOIRAE Spectrum Analysis Rou- tine. ...... .................. 49 2.3.l.C. Gamma—Ray Energy and Intensity Measurements................. 51 2.3.2. Double and Single Escape Peaks......... 52 2.3.3. Gamma—Gamma Coincidence Spectra........ 53 Decay Scheme Construction...................... 55 2.4.1. DECAY SCHEME Program ......... .......... 55 2.4.2. TAKE CARE Program ..... . ........ ........ 56 2.4.3. Auxiliary Programs..................... 57 Plotting Routines.. ..... ...... ....... .......... 62 2.5.1. Program VALTAVA ..... ................... 62 2.5.2. Program COINPLOT... ................ .... 63 EXPERIMENTAL RESULTS......... ..... .................... 66 Electron Capture Decay Scheme of B1204.......... 66 3.1.1. Introduction... ........ . ......... ....... 66 3.1.2. Source Preparation..... ........ . ..... ... 67 3.1.3. 31204 y—ray Spectra ..... ................ 68 68 3.1.3.A. Singles Spectra............... l 3 3.1 Chapter 3.1.4. Page 3.1.3.B. Anti-coincidence Spectra ..... 78 3.1.3.C. Double Escape Coincidence Spectra ...... . ...... . ........ 80 3.1.3.D. Prompt—coincidence Spectra... 83 3.1.3.E. Delayed—coincidence Spectra Experiments... ............... 88 Construction of the szou Level Scheme. 89 3.1.4.A. 899.2—keV Level .............. 92 3.1.4.B. 1273.9—keV Level ............. 92 3.1.4.C. 1562.8-keV Level ............. 94 3.1.4.D. 1817.3—keV Level ............. 94 3.1.4.E. 2065.1— and 3768.4—keV Levels 95 3.1.4.F. 2185.4—keV Level ............. 96 3.1.4.G. 2257.9«keV Level ............. 97 3.1.4.H. 2385.8—keV Level ............. 98 3.1.4.1 2480.0—keV Level ............. 98 3.1.4.J. 2506.8—, 2919.5—, and 2925.5— keV Levels ................... 99 3.1.4.K. 3029.0— and 3092.0~keV Levels 100 3.1.4.L. 3104.9—keV Level ............. 101 3.1.4.M. 3170.9—keV Level ............. 101 3.1.4.N. 3215.0—keV Level ............. 104 3.1.4.0. 3232.0—keV Level ............. 106 3.1.4.P. 3637.8-keV Level ............. 106 3.1.4.Q. 3782.0—keV Level ............. 107 3.1.4.R. 3814.4—, 3826.2-, 3842.2—, 3875.7—, 3996.1-, 4080.5—, and 4249.6—keV Levels ........ 107 vi Chapter Page 3.1.4.5. 2434.0—keV Level ...... ....... 107 3.1.4.T. 4165.5-keV Level............. 108 3.1.4.U. Comments.. ......... . ...... ... 109 3.1.5. Electron Data and Multipolarities...... 154 3.1.6. Spin and Parity Assignments for szou.. 159 3.1.6.A. Ground, 899.2—, 1273.9~, and 2185.4—keV States ..... . ...... 163 3.1.6.B. 1562.8-keV State ...... . ...... 164 3.1.6.C. 1817.3—keV State ...... . ..... . 165 3.1.6.B. 2065.1-keV State ............. 165 3.1.6.B. 2257.9—keV State ............. 166 3.1.6.F. 2385.8—keV State..... ....... . 166 3.1.6.C. 2434.0—keV State....... ..... . 166 3.1.6.R. 2480.0—keV State..... ...... .. 167 3.1.6.1. 2506.8-keV State.. ..... ...... 167 3.1.6.J. 2919.5—keV State ............. 167 3.1.6.K. 2928.5—keV State...... ....... 168 3.1.6.L. 3029.0—keV State ............. 168 3.1.6.M. 3092.0-keV State ............. 169 3.1.6.N. 3104.9—keV State ............. 169 3.1.6.0. 3170.0—keV State ......... .... 169 3.1.6.F. 3215.0-kev State ............. 170 3.1.6.Q. 3232.0—keV State ....... . ..... 170 3.1.6.R. 3637.8—keV State ............. 170 3.1.6.8. 3768.4—keV State ............. 171 vii Gunter Chapter Page 3.1.6.T. 3782.0-keV State ...... . ........ 171 3.1.6.U. 3814.4-, 3826.2—, 3842.2—, 3875.7—, 3996.1-, 4080.5—, 4165.5-, 4249.6—keV States ..... 171 3.1.6.V. Comments..... ...... ............ 172 3.2. Electron Capture Decay Scheme of B1203.......... 174 3.2.1. Introduction ......... . ......... ......... 174 3.2.2. Source Preparation........ ..... . ........ 176 3.2.3. 31203 y—ray Spectra ..... ................ 176 3.2.3.A. Singles Spectra.. ............. 176 3.2.3.B. Anti-coincidence Spectra ...... 183 3.2.3.C. Double Escape Coincidence Spectra... ..... . ....... .. ..... 185 3.2.3.D. Prompt—coincidence Spectra.... 138 3.2.3.E. Delayed—coincidence experiments ....... . ........... 190 3.2.4. Construction of the Pb203 Level Scheme.. 191 3.2.4.A. 825.2-keV Level ............ ... 193 3.2.4.3. 126.4— and 186.4-keV Levels... 193 3.2.4.C. 820.2—keV Level ............. .. 195 3.2.4.D. 866.4-keV Level ......... . ..... 198 3.2.4.E. 896.9— and 1160.8—keV Levels.. 198 3.2.4.F. 1033.6-keV Level ..... ......... 199 3.2.4.C. 1547.6— and .641.6—keV Levels. 200 3.2.4.E. 2033.8—keV Level .............. 201 3.2.4.1. 2184.0—keV Level .............. 201 3.2.4.J. 2387.8—keV Level .............. 202 viii r e t P .W Chapter 3.2.5. 3.2.6. 3.2.4.1<. 3.2.4.L. 3.2.4.14. 3.2.4.11. 3.2.4.0. 3.2.4.P. 3.2.4.0. 3.2.4.R. 3.2.4.8. 3.2.4.T. 2568.9-keV Level.. ...... .... 2620.5—keV Level ...... ....... 2667.8—keV Level............. 2713.4—keV Level........ ..... 2748.7—keV Level....... ...... 2753.4—keV Level...... ....... 2793.7—keV Level............. 2821.1—, 2964.4-, and 3016.9- keV Levels.............. ..... 3045.2—keV Level... .......... Comments........... .......... Electron Data and Multipolarities...... Spin and Parity Assignment for Pb203... 3.2.6.A. 3.2.6.E. 3.2.6.C. 3.2.6.D. 3.2.6.E. 3.2.6.F. 3.2.6.G. 3.2.6.J. 3.2.6.K. 3.2.6.L. Ground, 820.2—, and 825.2— keV States ................... 126.4- and 186.4—keV States.. 866.5—keV States ..... . ....... 1033.6—keV States ..... . ..... . 896.9— and 1160.8—keV States. 1547.6— and 1641.6—keV States 1802.4- and 2033.8-keV States 2184.0— and 2387.8—keV States 2568.9—keV State.... ......... 2620.5— and 2748.7—keV States 2667.8—keV State ............. 2713.4—keV State ............. ix 206 208 209 242 242 244 245 245 246 247 248 249 249 249 250 250 (bapter Chapter Page 3.2.6.M. 2753.4-keV State............. 251 3.2.6.N. 2793.7—keV State ....... . ..... 251 3.2.6.0. 2821.1—, 2964.4—, and 3016.9- keV States .......... . ....... . 252 3.2.6.P. 3045.2—keV State.. ........... 253 3.2.6.0. Comments ..... . ......... ...... 253 IV. DISCUSSION OF RESULTS... ..... ... ......... ....... ..... 254 4.1. Comparison With Other Investigations ........... 256 4.1.1. Pb20H Experimental Data ............... . 256 4.1.2. Pb203 Experimental Results .......... ... 257 4.2. Shell—Model Characteristics of the szo“ and Pb203 Level Schemes .......... . ........... . ..... 262 4.2.1. Nuclear Level Spacings in the Pb Region near Pb203’201+ ..... . ......... ..... ..... 263 4.2.2. Discussion of Pb203 Results............ 269 4.2.2.A. P13203 Excited States — Shell Model States ................. ' 269 4.2.2.B. B1203 8 Transitions .......... 275 4.2.2.C. Conclusions .................. 279 4.2.3. Discussion of Pb“)!+ Results. ........... 280 4.2.3.A. Shell—Model Calculations on P1320" ............... 280 4.2.3.B. 1313201+ Excited States and 31204 8 Transitions.. .............. 287 4.3. General Summary ..................... . .......... 291 BIBLIOGRAPHY ..................... . ............................ 293 APPENDICES ..... . .............................................. 299 A. TAKE CARE FORTRAN Listing .................... . ...... 299 x Chapter 3. VALTAVA C. COINPIDT Page VMfifimEmummtaungu.u.nn.u.nn.uu.un.3m C. COINPLOT FORTRAN Listing............................ 307 xi Table 10. LIST OF TABLES Table Page 1, Summary of the present state of knowledge of transi— tions and levels in some of the light lead isotopes. 5 2. Experimental half-lives for 31204 decay... ......... 21 3. Experimental half-lives for B1203 decay...... ..... 28 4. Q values for T1203’205(He3,xn) reactions.... 9. Ratio of the 440.3- keV y to the 984.0—keV y in the 670— and 911— keV coincidence Spectra.. oo-ooonooooc 10. Multipolarity of BiZOL+ y transitions...... ........ ..... 180 13. Results of the 31203 anti—coincidence experiment.... 186 14. Multipolarity of B1203 y transitions..... 15. xii Table 16. 17. 18. 19. Table Page 16. Comparison of Pb204 excited states revealed by_scat— tering reactions wit h those of present study......... 258 17. Comparison of Pb2°#(d,t)Pb203 scattering data to the present study...................... ..... ... . . ...... 261 18. Possible neutron configurations for some low-lying excited states in Pb203.......................... . 276 19. Single-hole energies in Pb207 and Pb203... ....... . . 286 xiii Figure ll. Pb205 Level Scheme [K070] 5. PbZO‘V” Decay Scheme [Fr58]...... ...... analysis routine SAMPO puter. The fit is to a 212— decay of B120”. Oscilloscope display of a portion of the 8120“ SpeCtrum, as run under the program MOIRAE made on Fig. 11 ..... xiv Ion..- non-00...... I‘Ooaottolol , as run on the Sigma—7 com— 222-keV quartet from the y-ray onto-0...... Page 16. 15. Figure Page 13. Display of peaks (including the quartet of Fig. 10) after the calculated fourth-order background has been subtracted............................................ 50 14. A portion of the TAKE routine line~printer output from the TAKE CARE program. The energy levels (on the left, in keV) and gamma—ray energies (in keV) are from the present 3120” decay scheme studies. The nonzero ener— gies in the 4 columns to the right of the energy levels correspond to gamma rays whose energies are within a specifiable tolerance (here 1 keV) of the energy diff— erence between the tested level (e.g. "LEVEL 1944.60") and the levels in the left—hand column................ 58 15. A portion of the CARE routine line—printer output from the TAKE CARE program. The energy levels and gamma—ray energies are from the 8120” decay scheme studies............................................... 59 16. 3120” singles y—ray spectrum taken with a 2.5% Ge(Li) detector having a resolution of 2.4 keV FWHM (at 1.33 MeV) in this run...................................... 73 17. The previously proposed tentative decay scheme for 13120“ [St58] 79 18. Experimental setup for recording anti— and double escape (511—511—7) coincidence spectra. For a 511— Sll—y coincidence spectrum the TSCA's are adjusted such that the window falls on the Sll—keV region and the linear gate is the normal mode. For an anti-coin— cidence spectrum the TSCA's are wide open and the linear gate is in the "anti” mode..................... 81 19. 3120“ double escape spectrum taken with the NaI(Tl) split annulus and a 7 cc Ge(Li) detector having a res— olution of about 4 keV (FWHM at 1.33 MeV) in this run 82 XV 23. 24‘ The Y ..— Figure ' Page i 20. BiZO“ integral coincidence spectra taken using the multiparameter Ge(Li)-Ge(Li) spectrometer (section 2'2.2.BI)¢000|0I00|0IO'OIIOOOIUOIflOOCC..IIQOIIQOODUIDO 84 21. Two coincidence spectra (from the B1203 decay) illus— trating the effectiveness of background subtraction in the EVENT RECOVERY program. (The spectra were pre- pared using the VALTAVA plotting routine described in section 2.5.1.).................................... 87 22. The a decay scheme of 131201+ proposed by the present study. All transitions were placed using coincidence data alone, without the use of energy sums............ 90 23. Triton spectrum of the Pb206(p,t)Pb20L+ reaction ob- tained at 90° with 22 MeV protons [Ho69].............. 93 24. The y—y coincidence spectra from the B120“ decay. The spectra were recovered from the coincidence data stored on magnetic tapes using EVENT data—taking rou— tine. Sample titles of the coincidence spectra and their meanings are found below: lOO-KEV GATE: A gated region from which background has not been subtracted; lOO-KEV GATE WITH BKGD SBTD: A gated region from which background has been subtracted; lOO—KEV BKGD ONLY: Spectrum of the background adjacent to the 100—keV gated region. Unless otherwise specified, all spec— tra are displayed from the X axis..................... 111 25. The level scheme of Pb201+ showing additional trans— itions from the 3120“ decay which could be placed on the basis of precise energy sums and differences a- lone. The tolerance allowed for the left side of the figure was i0.25 keV for y's having energies <15OO keV and i0.30 keV for y's having energies >1500 keV. The tolerance for the right side of the figure was 10.5 keV. A semicircle at the origin of a transition xvi 27' 1’"Wiousl 23. “20‘: 29, BifGB 30. 51203, . Figure Page indicates some coincidence data support for such a placement........................................... 152 26. Experimental conversion coefficients for some PbZO” transitions. The smooth curves of the theoretical aK were prepared from tables in [$165]................... 157 27. Previously reported B1203 decay scheme [No58]......... 175 28. B1203 singles y-ray spectrum taken with a 3.6% detec— tor having a resolution of 2.1 keV FWHM (at 1.33 MeV) in this run........................................... 178 29. B1203 anti—coincidence spectrum recorded by the 2.5% Ge(Li) detector when placed inside the tunnel of the NaI(Tl) split annulus with a 3"x3" NaI(Tl) detector at the other end of the tunnel........................ 184 30. B1203 integral coincidence spectra taken using the multiparameter Ge(Li)—Ge(Li) spectrometer (section 2.2.2.3.). The X and Y spectra were taken with the 3.6% and 2.5% Ge(Li) detectors, respectively.......... 189 31. The e decay scheme of B1203 proposed by the present study. All transitions were placed using coincidence data alone, without the use of energy sums............ 192 32. Low energy spectrum of 31203, taken with a Si(Li) x— ray detector. A partial list of Pb L x—rays is in- cluded. ......... .............. ...... .................. 197 33. The y—y coincidence spectra from the B1203 decay. The spectra were recovered from the coincidence data stored on magnetic tapes using EVENT data~taking rou— tine. The titles of the coincidence spectra have the same meanings as those in Figure 24................... 210 34. The level scheme of Pb203 showing additional trans— itions from the B1203 decay which could be placed on xvii figure 15. 36. 37. 38. the basis Figure Page 1 the basis of precise energy sums and differences a— lone. The tolerance allowed was i0.25 keV for y's having energies <1500 keV.and $0.30 keV for y's hav— ing energies >1500 keV. A semicircle at the origin of a transition indicates some coincidence data sup- port for such a placement............................. 235 35. Experimental conversion coefficients for some Pb203 transitions. The smooth curves of the theoretical 7K were prepared from tables in [Sl65]................... 239 36. Systematics of the low—lying l/2+, 3/2+, and 5/2+ states in odd-mass Tl isotopes. These should be relatively pure 81/2, d3/2, and d5/2 shell—model states................................................ 265 37. Systematics of the fS/z, pl/Z’ p3/2’ and i13/2 states in the odd—mass neutron~deficient Pb isotopes......... 266 38. Compilation of experimental and theoretical data for th the fS/z’ p3/2, and pl/2 neutron level spacings 1n the lead region.......... ....... .......................... 267 39. Shell—model orbitals near N=121 and Z=82.............. 268 40. The energy levels of PbZO” calculated by True [Tr56] according to the model formulated by Pryce [Pr52]..... 282 41. The energy levels of Pb201+ as calculated by Kisslinger and Sorensen [K160].' 0n the left are the labeled un- perturbed states. For each spin the horizontal line to the left gives the energy of the state; the second horizontal line shows the effect of the inclusion of the P2 force. The lines to the right are a few ex- perimental levels. The level marked [2+] is the collective 899.2—keV level.......... ...... ............ 282 xviii 42. Theoretical neutron level spacings in the lead region as calculated by Kriechbaum and Urban [Kr68]. Re- sidual interactions were approximated by a short— range pairing force and a long-range quadrupole plus octupole force. The small black dots are the theo~ retical values. The large open circles are ex— perimental values.... .......... ....... ..... ... xix CHAPTER I INTRODUCTION Nuclear models, abundant as they are with empirical param— eters, provide a significant measure of our understanding of nuclear structure. Since these nuclear models are at least partially based upon experimental data, any increase in the quality and/or quantity of experimental results can greatly aid in the testing of the appro- priate theoretical model. Moreover, while experimental observations are a necessary test of theory, they can also function as stimuli for preparation of improved models. The investigations included in this thesis are therefore intended to extend and improve significantly the information acquired from the radioactive decay of B1203 and 31204 through high—resolution gamma—ray spectroscopy, thereby aiding in the task of understanding something of the inner structure of these nu— clei and in the development of more sophisticated nuclear theory. For a more complete appreciation of and insight into the experimental results found in this thesis a consideration of the Pb isotope sys— tematics in general and Pb203 and szo"1 in particular is essential. 1.1. General'Survey'of'Pb‘lsotope'systematics Unlike the transuranium isot0pes which are far removed from the "magic" closed shells and hence spheroidal rather then spherical in shape, the nuclei in the vicinity of the doubly closed nuclide szoe-are nearly spherical, and the nuclear shell model should work very well in predicting and describing the properties of individual levels in nearby nuclei. Since these nuclei are strongly stabilized in spherical shapes, the collective modes of excitation would be expected to appear at higher energies than for most nuclei; the lower levels then should be interpreted quite well as single—particle or few—particle states. This treatment has been done for several varied and reasonably successful calculations; these will be discussed later in this thesis when a correlation between the experimental data and the theoretical predictions is proposed. Unlike other regions of the Chart of Nuclides, the lead— bismuth region of interest (Figure 1) indicates deceptively simple modes of decay. For example, since there is virtually a total ab— sence of appreciable alpha decay, one is relieved of the difficulties of resolving the genetic relationships. The predominant reason for this lack of alpha decay is that the large binding energy per nucleon associated with the closed shells makes the energy available for alpha decay so small as practically to eliminate this as mode of de— cay. Consequently, the lead and bismuth isotOpes having N<126 have particularly low alpha—decay energies; in fact, with the possible exception of Pb20“ for which an alpha group of 2.6 MeV and 1.4><1017 year (y) half—life (tl) [R158] has been reported, no alpha activity 2 Fig. 1. yMlI‘I, 12— 261026. .99) Portion of the Chart of Nuclides, including the lead—bismuth region of interest in this thesis. Taken from the Chart of Nuclides compiled by the Knolls Atomic Power Laboratory, Ninth Edition. men detected in the 1°" I ..., u=190) are raw) ' up» the very low A) aha on”? have long half-life mlisouth isotopes 31203 h lim,a0.003l, 5.5 Hell alph lump [NeSO]. None at a] hm and 31200 isotopes. Since the nuclei 1 MW node of decay is l: billed, however, the system aMot simple at all. Tab? “hating the light lead is isomeric decays. The refer atue data and unpublished lithlgan State University. u 5t recent or thorough bu inf When was obtained . hasbeen detected in the low mass (A<210) Pb isotopes (until very light nmsses (A3190) are reached). The light Bi isotopes having A=198—201 (and also the very low A) show a slight alpha branching, while 31203 and 31209 have long half—life alpha activities. In these light odd— mass bismuth isotopes 31203 has a lO‘SZ, 4.85 MeV alpha group [Du52];> 31201, a 0.00374, 5.5 MeV alpha group; and 31199 has a 0.01%, 5.54 Nev group [NeSO]. None at all has been reported for the even—mass 31202 and 31200 isotopes. Since the nuclei in this region are neutron deficient, the principal mode of decay is by orbital electron capture (6). As was implied, however, the systematics and decay schemes of these nuclei are not simple at all. Table 1 shows the progress to date in de— ciphering the light lead isotopes from Pb207 to Pb203, including the isomeric decays. The references included are both published liter— ature data and unpublished results from the investigations at the Michigan State University. The reference(s) given is generally the most recent or thorough but not the sole reference from which the information was obtained. An outstanding reference for a survey background of the lead—bismuth region is the excellent review by Hyde, Perlman, and Seaborg [Hy64]; this review was used as a point of departure for a study of this region. Included in this region is the highly interesting doubly closed shell nucleus Pb208. Being (dosed at both Z=82 nnd N=126 major shells,onc would expect Pb70” to be particularly stable, and in truth such is indeed the case, even to the point of being the end product of the An naturally occurring radioactive decay chain. As one or more neutrons are removed to produce the lighter, neutron—deficient lead isotopes, the spectra Table 1. Smary of th‘ sitions and 1‘ =—_—,——___————===-= 31207 B [A155] l Table 1. Summary of the present state of knowledge of tran— sitions and levels in some of the light lead isotopes 31207 B1206 31205 3120“ B1203 [A155] [Ve63] [K070] [Present] [Present] 2‘: 27 y 6.4 d 15.3 d 12 h 12 h NI— Q (MeV) 2.40 3.7 2.67 4.4 23.2 EC +0. 04 No. of known tran— 100+ sitions No. placed in level scheme No. of known levels No. of well— character— 5 >14 ized levels ”I _m m Pb207m szosm Pb205 PbZOLi Pb203 [Mc53] [A153,A154] [St60a] [He56] [D068] j 145 us 4.5 ms Excited- state 1633.1 2200. 3 1013.8 energy (keV) No. of known transitions 6.1 s 825.2 Table 1. (continued) No. placed in level scheme No. of known levels No. of well- characterized levels the increasingly “‘91” d‘ motions and configuration 1 haietailed test of the th lav; spherical nuclei. lhe first coupliCi island in practically all t hl=126 closed shell is ob £1312 state being lowered by $3, odd-parity states froo Fifi: [5/2, f7/3, and h9/2,< mi large Spin different Didmass lead isotopes rang ”‘9 comIllicated configurat and l on”13/2 hole. The e nth er even~even isomers art bmmme increasingly complex due to single or multiple hole—hole in— teractions and configuration mixing, thus providing exciting candidates for a detailed test 'of the theoretical interparticle force concepts of heavy spherical nuclei. The first complication, the existence of nuclear isomerism, isfound in practically all of the light lead isot0pes. Recalling that Hm N=126 closed shell is obtained in the Spherical shell model by the {13/2 state being lowered by spin—orbit coupling to lie among the low— spin, odd—parity states from the fifth oscillator level, i.e. Pl/Z, p3/2, f5/2, f7/2, and h9/2,one would expect to find near—lying levels having large Spin differences, hence producing nuclear isomerism. The odd—mass lead isotopes range from the single—hole i13/2 Pb207m to much more complicated configurations, but in all cases they have even parity and one i13/2 hole. The even—even lead isomers are unique in that no other even—even isomers are known; in these even—even lead isotopes each metastable isomer is composed of one i13/2 hole,but here each is coupled to an odd number of odd-parity holes to produce odd-parity states. Since the other even-even lead isotope levels are even parity, flfls coupled with the large spin differences gives rise to the nuclear isomerism. 1.2. L‘ ____——— Pollmdng this 8 memo to examine briefl pttobedone on the other helschenes of Plow" and l heemclides is naturally his abbreviated discussion interest in this region of 1.2.1. szoa Level Scheme \ szns’ being c3 isstahle, having no low-1' '03 W nucleus would be exp Vihations [Hy64], and no 8 1.2. Lead Level Schemes Following this general survey of the lead systematics,I now return to examine briefly the work which has been done and needs yet to be done on the other lead isotopes leading up to the complex level schemes of szol’ and Pb203. A truly comprehensive treatment of these nuclides is naturally beyond the scope of this thesis, but even this abbreviated discussion serves to illustrate the reasons for interest in this region of nuclides. 1.2.1. szo8 Level Scheme szoe, being closed at both the Z=82 and IV=126 major shells, is stable, having no low-lying excited states. Consequently, the Pb208 nucleus would be expected to be very stiff towards collective vibrations [Hy64], and no states due to these vibrations are expected to fall less than several MeV. The best evidence for this unusual ri- gidity is seen in the energy of its first excited state. The first excited state at 2615 keV is greater than the energy of any yet re— ported first excited state of nuclei with mass greater than 40 atomic mass units (amu). Indeed, the first excited level is a 3- octupole os- cillation state of the core [L360], not a proton excitation state as was once proposed [Tr58] . The level scheme for this isotOpe is also unique for an even-even nucleus in that the two lowest-lying states do not have the usual 2+ and 4+ character. The lowest levels of szos and their spins and parities are 0 (0+), 2615 (3-), 3198 (5—), 3475 (4—), and 3700 (5-) keV [E154]. For a more impressive discussion of Pb208, in— Cluding the preparation and description of its levels, in terms of idols particle-hole shell dz excellent background ref W Tue excited “>201 tiedettron capture decay < dens which satisfies the pi hm, differing by only on Should correSpond directly me. From simple shell no it}; ground state with f5/; the states correSponding ' 207 Mb . Indeed, this is theta/2 level at 3.47 PM Glue of the energetics of IEdoubly well as single- 4:.9‘9 41.512) transition rat complex particle-hole shell model configurations, one should turn to the excellent background reference of Hyde, Perlman, and Seaborg [Hy64]. 1.2.2. 1315207 Level scheme The excited Pb207 levels (Figure 2), as revealed [A155] by the electron capture decay of B1207, make a classic example of a nu— cleus which satisfies the pure Single—Particle Model. The states in Pb207, differing by only one neutron form the stable szo8 core, should correspond directly to single neutron holes moving in the Pb208 core. From simple shell model predictions one would anticipate a [91/2 ground state with 305/2, 293/2, 7113/2, 307/2, and 729/2 excited states; these states corresponding to the 570—, 870—, 1634—, and 2035-keV levels in Pb207. Indeed, this is exactly what was found empirically, although the 719/2 level at 3.47 MeV is not populated by the Bizo7 decay be- cause of the energetics of the situation. These levels behave reasonably well as single-hole states, the isomeric M4 (1064 keV, 7313/2+f5/2) transition rate being fairly close to that predicted by the Weisskopf estimate [WeSl]. The fact that the 570—keV transition to the ground state is abnormally fast for a neutron transition can be eXplained [Pr56] by a slight collective effect in the spherical nucleus. 1.2.3. Pb206 Level Scheme In contrast to the simple l’byO7 scheme, the Pbym‘ level scheme (Figure 3) is quite complex, since Pb?“ is two neutrons from the doubly closed Pb208. Nevertheless, there is a fundamental sim— Plicity to the 'level scheme in that most of the known levels are 0.80 s Fig. 2. Fig. 3. 10 OLC 1‘0 41”. 0“ 3.14 (..l. 32"sz7 Pb2°7 Level Scheme [A155] 206 82Pb Pb206 Level Scheme [Ve63] Illdmntetizing the Pl) hide, but essentially filing the ve11~placed lave b”then Iade on this is 1late of Pbm in these c Mutions: l) the sun single—h 2) the hole M 3) the conf same spi These calculations vary V “118ng from interaction tbulge forces to a simp] IMs technique, however are small and when the isso large that it dOE isotope. The first by“ True and Ford [TrSBl , tental Pb“)6 levels, 1: ll derivatives of the single particle (hole) states in Pb207. An odd- odd nucleus,-Bi206 has a decay energy of 3.7 MeV and consequently pop— ulates many high—lying states of varying complexity. The most compre- hensive decay scheme to date was proposed in 1954 by Alburger and Pryce [A154],who successfully placed 27 Pf the 28 transitions found and assigned many multipolarities from conversion coefficients, thereby well characterizing the Pb206 levels. Some small improvements have been made, but essentially the decay scheme must be considered complete. Using the well—placed levels in szos, several shell model calculations have been made on this isotope [Pr52,Tr58,Ke57]. The energy of any state of Pb206 in these calculations is actually the result of three contributions: 1) the sum of the energies of the two corresponding single-hole states in Pb207, 2) the hole-hole interaction energy, and 3) the configuration mixing between states having the same spins and parities. These calculations vary widely in the degree of their sophistication, ranging from interactions involving complex potentials with added ex— change forces to a simple delta—force interaction between the two holes. This technique, however, is useful only when collective modes of motion are small and when the energy needed for excitation of the core nucleons is so large that it does not influence the low—lying states of the isotope. The first type potential, represented by the calculations of True and Ford [Tr58], indicates excellent agreement with the exper— nmntal Pb206 levels, but only after assuming some collective enhancement we pairing force, also Major advantage of th lighter lead isotopes, vb hue honendously cunbe lighter lead nuclei. 1.2.4. 1115205 Level Sch As one moves 126 closed shell, the sit 5316mm elaborate inves‘ including detailed coinc conversion-electron spec he latter, by studying distinquish between the Sltions, were able to f Huber of observed trar Ema coincidence meas‘ éfknown levels in 1’52 thorough investigatim 12 of a number of the gamma—ray transition probabilities, even to the extent that two levels had to be characterized as vibrational states. Other simple calculations, such as those devised by Kisslinger and Sorenson [K160], based upon treating the residual two-nucleon inter- action as a BCS [Ba57] superconductivity pairing force plus a long range pairing force, also lead to at least qualitatively good results. The major advantage of the latter is its applicability to many of the lighter lead isotopes, whereas the True and Ford exact calculations become horrendously cumbersome. Since the Kissinger and Sorenson re— sults are at least qualitatively correct for szoe, one would expect at least qualitative validity for their predicted levels in the lighter lead nuclei. 1.2.4. szos Level Scheme b205 As one moves to P , three neutrons removed from the N: 126 closed shell, the situation becomes very much more complicated. Numerous elaborate investigations of Bi205 decay have been reported, including detailed coincidence studies [Sc6l,He6l] and the extensive conversion—electron spectroscopy of Vegors, Heath, and Proctor [Ve63]. The latter, by studying the half—lives of the transitions so as to distinquish between the 6.4-day (d) B1206 and the 15.3—d Bi205 tran- sitions, were able to find 42 new transitions, bringing the total number of observed transitions to 83. Using extensive NaI(Tl) gamma— gamma coincidence measurements, they were able to extend the number 0f known levels in Pb205 from 13 to 22. Perhaps the latest and most thorOugh investigation of Pb205 is the soon-to—be—published work of Met, there is a 13/24- hlf-life is just 4.5 ail mtnlld leaner (in/2"; “”2- states now lie b “Jasequmtly, M2 and M3 t half-life. Second, there W. Since there are null thmound and first excl hublets of peaks differi Version—electron spectra. detractors, but with the 2 my can be resolved . Similar to Pb2 been made by True [Trfill MO]. Despite the SU‘ levels would lie below inlations are not at 31 Energy spacings, much 1 it necessary to modify anllebeven potent ial l3 Kosanke, McHarris, and Kelly [K070] at Michigan State University. Using high-resolution gamma Spectroscopy and Ge(Li)—Ge(Li) coinci— dence experiments, they have made significant changes and improve— ments in the Pb205 decay scheme (Figure 4). Pb205 is distinquished from the other lead isotOpes in this region by several peculiar characteristics. Just as one would expect, there is a l3/2+ isomeric state at 1014.0 keV; however, its half-life is just 4.5 milliseconds (ms). This occurs because it is not an M4 isomer (i13/2~if5/2) any longer; rather three—particle 9/2— and 7/2- states now lie between the isomer and the 5/2— ground state. Consequently, M2 and M3 transitions complete with the lOl4—keV M4's half—life. Second, there is a low—lying first excited state at 2.3 keV. Since there are numerous high-lying levels which populate both the ground and first excited state the spectrum is abundant with doublets of peaks differing by 2.3 keV. Although seen in the con— version~electron spectra, it is hepeless to resolve them with NaI(Tl) detectors, but with the advent of high-resolution Ge(Li) detectors they can be resolved. Similar to szoe, shell model calculations on Pb205 have been made by True [Tr61], Pryce [Pr56], and Kisslinger and Sorenson [K160]. Despite the success of predicting that the 9/2- and 7/2— levels would lie below the 13/2— state, the results of these cal— culations are not at all convincing. In attempting to fit the energy spacings, much less the transition probabilities, True found it necessary to modify his original calculations (which used a Singlet-even potential with a Gaussian shape) into calculations using ...... l ——_———“n_“—“— al.\h.l.\°u ”an“ I. I I ”Infill. I lllllllllllllllllllllllllllllllllll .... 3:. En ,.. .. -IllllIlI‘lilill. . '\. ...°.. - 14 3 mm: -N\m 0.0 now. .mwmnw mNm .NB 0.0 - ~\_ nu iuxn @qu umxn 0.650 aNxs. v.no~. IN).- v.55 uuxo 0H8 ouxn _ 0.0.0. uwxh Ento— TNBJB. meow. szos Level Scheme [K070] u Nxo Nam! ouxm rtnmo. out Ahia— wanflwxn. ..mnt .8». €th Tuxnruxfl 0.2L.— .. ... .. . mmw n . u. . .. 0 VNE I —— m llllllllll TNPFNxQ n.NmVN , 0.35: .mnmm-m—II [mew IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII em; «.33 - — - m ___ mmmwme o «\a Qwomu w Fig. 4. (If) (V0) (I'll as'mglet-even potenth neck coupling to the all the calculations hi to lie so close to the ital calculations of P1 sophisticated calculat: 1.2.5. Pbm Level Scl \ 15 a singleteeven potential of three—quarters the original value plus a weak coupling to the nuclear surface. The monumental failure of all the calculations has been in failing to predict the 1/2- state to lie so close to the ground state. Surprisingly, the semi-empir— ical calculations of Pryce come closer than do the more complex, sophisticated calculations. 1.2.5. szou Level Scheme If one were to remove four neutrons from the szoa N=126 closed shell, it would be expected that the complexity of szo“ should be still greater than Pb205 and szoe, because the nucleon— nucleon interactions and the configuration mixing will be greatly increased. The ground state of PbZO” is stable, occurring in 1.48% isotopic abundance in natural lead. Since PbZO” is not the product of any naturally occurring radioactive decay chain, PbZO” content can be used as a guide for the primeval lead content in any natural lead sample. The level scheme of this nucleus is also of great in— terest in furthering our understanding of the shell model predictions near the Pb208 double closed shell. As previously mentioned, Pb20L+ has been reported to have a measurable half—life for alpha decay. Using nuclear emulsions with enriched szoi Riezler and Kauw [Ri58] observed an alpha group of 2.6 MeV and a half—life of 1.4X1017 y- The excited states of PbZOH are populated, and hence re— vealed, by the gamma—ray cascades from the 66.9 minute (m) isomeric 2186-keV szoum and also by the ll.5-h electron capture decay of Bizo”. An upper limit of 0.6% positron feeding has been reported [166], while the mesa <0.11. 'lhe existing ex] bestand my published inthis thesis. The im two-step procedure, fir: “195120“ decay, but no; Pom isomeric decay. w 16 [Fr56], while the present data indicate a much smaller upper limit, <0.1Z. The existing experimental work was incomplete and sketchy at best,and many published results are seriously questioned by the work in this thesis. The investigation of Pb20l+ has been essentially a two-step procedure, first determining the isomeric decay and second the B120# decay, but most of the past work has centered upon the Pb2°“m isomeric decay. 1.2.5.A. szoum Isomeric Decay The 66.9 m szoum isomer has been made by the following re— actions: T12°3(d,n)Pb20L*m T12°5(d,3n)1=b2°‘+’” P1320” (n,nl)Pb20'-im Pb201+(d! 2n)3120l+_£_,Pb20um References to this early szoqm work are given in refer- ence [H053]. The early work limited the mass assignment to szo” or prOS but favored the szou. The final mass assignment was made certain by the mass separator experiments of Thulin [Th54]. This was of extreme interest at the time because szoum was the first even— even isotope found to have a long—lived isomeric state. Unlike the 312°” decay, the szoum isomeric decay has been well—investigated, be- ginning with Sunyar et al. [SuSO] in 1950. The conversion—electron spectroscopy, electron—electron, and gamma-gamma [Kr54,Kr55] prompt— and delayed—coincidence data indicate the 912—, 375—, and 899—keV gammas are in cascade. Fritsch [Fr56] found the Pb70“m decay scheme somewhat lore couplex; b aim; the electron ape spectrograph, he fomd a sition with the K/L and sitiun. Based upon this cated below the 2186-keV depopulated by a 622-keV isdepopulated by the 28 keV level. These same c l7 somewhat more complex; by separating the Pb20”m from 312°1+ and ex— amining the electron spectrum in a high-resolution permanent—magnet spectrograph, he found a 289.5—keV gamma ray and a 621.7—keV tran— sition with the K72 and LZ/LZ/L5 ratios expected of an E5 tran- sition. Based upon this, he concluded that a new 4+ level was lo- cated below the 2186-keV 9— level, causing the 2186-keV level to be depopulated by a 622—keV gamma to a lS63-keV level, which in turn is depopulated by the 2894keV gamma to the well-established 1274- keV level. These same conclusions were reached and confirmed by Stockendal et al. [St58,St60]. The final szoum decay scheme to date is seen in Figure 5. The excellent angular correlation experiments of Krohn and Raboy [Kr55,Hu56] established the 9—4-2-0 spin sequence seen in this figure, but in doing so it was found necessary to assume multipole mixing in the gamma transitions. The 912-keV E5 gamma was determined to have 1% M6 admixture, and the 375-keV E2 gamma to have l/2Z ad— mixture of M3. Additional work [He56] revised this figure downward but still found it necessary to assume some multipole admixtures in these transitions. bZOHm No significant change in the P decay seen here has been suggeSted by the present work, although an interesting peculi— arity with the 912—keV transition will be mentioned shortly. 1.2.5.8. Electron Capture Decay of B120” 8120“, an odd-odd nucleus, has an estimated [Fr56] decay b201+ energy 0f 4.4 MeV and populates states in P almost up to this energy, Depending on whose calculations you choose,not only are 4+ 1563.4 289 MI 44’ I274.0 375 E2 2*——L]—‘ 899.3 899 ' E2 O*—LO IZZPb204 Fig. 5., szmm Decay Scheme [Fr58] Molotowhur'il ht collective effect Idem than for the l 510'! levels, the 011' ll! 399.2-keV 2+ stat! predictions and appeal next too excited statt sililar difficulties. high-lying states pas little goes through t (N) experiments per lJtlmugh both are 10+ be very different. Because the free sources are impel Prepared by cyclotron electromagnetically st Some of the reactions 91:2 0“ (p . n2 PbZDu (d, 2, T12 0 3 (O. s 3’ Since the PM“ and T high isotopic purity, 91'6pared simultaneous creasing effect ive CW and 27~y 131207. Sinc 19 there 70 to 80 four—particle (hole) states available for pepulation, but collective effects and levels become more important for this nucleus than for the heavier Pb isotopes. For example, consider the Pb2°”m levels, the only levels previously known with certainty. The 899.2—keV 2+ state cannot be reconciled with any four—particle predictions and appears to be a quadrupole vibrational state. The next two excited states, at 1274 and 1563 keV (both 4+) also present similar difficulties. Nearly all the gamma—ray cascades from the high-lying states pass through the 1274—keV state, while comparatively little goes through the 1563-keV state. This is also seen in the (p,t) experiments performed at Yale University by Holland [Ho67,H069]. Although both are 4+ states, their internal structure must obviously be very different. Because the B120” decay is so complicated, clean, impurity- free sources are imperative. In past investigations the sources were Prepared by cyclotron bombardments of Pb or T1 targets, enriched electromagnetically separated targets being much to ones advantage. Some of the reactions used were: Pb2°“(p,n)1312°” Pb2°“(d,2n)312°“ T1203(a,3n)312°” Since the szou and T1203 isotopes are ordinarily not available in high isotopic purity, other Bi isotope impurities are necessarily Prepared simultaneously. The common contaminants, in order of de— . -205 cteasing effective quantities, are the 6.4—d B1206, 15-3'd Bl ’ and 27—y 81207. Since 31203 has a half—life nearly identical to Ii‘“,itnom leojuotbelavthe Sueoft of ‘11 but signifi. the 312°” decay haS" I311 variations by . While no: two lost detailed on by kitsch and Roll at al. [St58], at th high resolution give lied entirely upon h tained from pemanen 0.21(Fritsch) and 0 Performed gama‘gm using NaI(Tl) detectI lam-ray spectra, e1 mmerical analysis or that the decay was s ”hm level scheme they published essen over 150 conversion transitions and 115 t Stockenda did publish a very F the levels populated 20 3120“, it was necessary to eliminate it entirely by using a cyclotron beam just below the threshold energy for its production. Some of the characteristics of the 3120” decay are perhaps of small but significant importance at this point. The half—life of the B120” decay has been measured to be about 11.5 hours (b), with small variations by different research groups, as seen in Table 2. While many people have investigated the B120” decay, the two most detailed studies were independently undertaken in the 1950's by Fritsch and Hollander [Fr56,Fr58] at Berkeley and by Stockendal et a1. [St58], at the Noble Institute in Stockholm. Since only very high resolution gives any degree of significant data, both groups re— lied entirely upon high-resolution conversion—electron spectra ob— tained from permanent-magnet spectrographs with energy resolutions of 0.2% (Fritsch) and 0.1% (Stockendal). In addition, both groups Performed gamma—gamma coincidence experiments to a limited extent using Na1(T1) detectors. Using these data plus scintillation gamma-ray Spectra, electron—electron coincidence spectroscopy,and a numerical analysis of energy sums, Fritsch and Hollander concluded that the decay was so complex that they could not hope to construct a szmi level scheme with any degree of confidence. Consequently, theY published essentially just a list of electron energies. From over 150 conversion electrons they made assignments for some 67 transitions and listed them in three confidence groups. Stockendal et al. found many of the same transitions and did publish a very preliminary decay scheme bUt emphasized that only the levels populated by the Pb2°”m decay are known with any assurance. table 2: 5'3 Fri Pei We: Stc lReference [Fr58] bReference [Pe47] cReference [HeS6] dReference [St60] 21 'Table 2. Experimental half—lives for 312°"+ decay Principal 3120” Investigator Half—life (h) Fritscha 11.0:o.5 Perlmanb 12:1 Wertheimc 11.6:0.2 Stockendald 11.22:0.1O aReference [Fr58] bReference [Pe47] cReference [We56] d Reference [St60] 1273 2) all love grou 3) abou 9- i and 4) a La A prelinin (indeed, the one vhiq Ge(Li) detectors show Vectigation, upon onc spectrum, using impro Copy, it was found th Previously believed. lam-ray and Ge(Li) Considered as having have wa'm states, “of incorrect. While she] 0f this thesis, the d tion devoted entirely We" shell model ca] 22 Based upon the previous 3120” work, several conclusions have been reached: 1) the first and second excited states lie high and correspond to the 2+ and 4+ levels at 899.2 and 1273.9 keV, respectively, 2) all gamma cascades pass through the 899.2-keV 2+ level with little or no direct feeding to the ground state, 3) about 10% of the B120” decay proceeds through the 9- isomeric state, and 4) a large number of populated levels lie above 2 MeV. A preliminary re—examination [Gr66] in the MSU laboratory (indeed, the one which prompted the present investigation) using Ge(Li) detectors showed B1201+ to be very complex. In the present in— vestigation, upon once again re—examining the 3120“ gamma—ray Spectrum, using improved high-resolution Ge(Li) gamma—ray spectros— copy, it was found that the 3120‘+ decay was even more complex than prev1°US1y believed. So complex, in fact, that the previous NaI(Tl) gamma—ray and Ge(Li) work (especially coincidence studies) must be cOnsidered as having relatively little worth, with exception of the knOWn PbZOHM states, and that the decay scheme was debatable, if “Ot incorrect, While shell model calculations are to be an integral part Of this thesis, the discussion of these will be deferred to a sec- tion devoted entirely to the comparison of experimental data to the prOH shell model calculations. 6:04) spectrum a useful in placing II lent changes in the learning note than one can lake only 11! of the high probabili Ge(Li) gene-gm on of the couple: Conpta ample: spectral. Tl dence and double esce Even upon scoplc techniques it establish a complete] need for preliminary astudy of the Pb2°6( Pluck out coupled-nan vork of levels in sz 1.2.6. Pb”3 Level S Removing y tI'Ims removed from t? last isotope of inter 23 The present investigation involving standard high—resolution Ge(Li) Spectroscopy single and coincidence experiments has been suc— cessful in placing many new levels in szo“ as well as making signif- icant changes in the previous decay scheme, and in the process in char- acterizing more than 200 gamma-rays. With such a wealth of transitions, one can make only limited use of energy sums and differences because of the high probability of accidental agreements. AlSO‘NaI(T1) vs. Ge(Li) gamma—gamma coincidence experiments are of little use because of the complex Compton backgrounds and gating difficulties in such a complex spectrum. This leaves Ge(Li) vs. Ge(Li) gamma—gamma coinci— dence and double escape spectrometers as the necessary tools. Even upon the completion of these high—powered spectro- scopic techniques it was concluded that it may not be sufficient to. establish a completely unambiguous level scheme for PbZO“. A great need for preliminary scattering data was seen; this was provided by a study of the Pb206(p,t)Pb20“ reaction which, having a tendency to pluck out coupled—neutron states, appears to yield a basic frame— work of levels in szou [H069]- 1.2.6. Pb203 Level Scheme Removing yet one more neutron from Pb20” (i.e. five neu— ttons removed from the N=126 closed shell), one finally reaches the last isotope of interest in this thesis, Pb203. The Pb203 isotope ticnlly simple (Figu Ie to lake no attenp The Pb2°3 ant reactions on T12 trons [Pb53], or as be prepared by yet 0 characteristics of t? investigations [St60 aVariety of experim 3.6.3. The 6.1—s covered by Hopkins [ 1955, Fischer [F155] of excitation functi fixation [smomrse comission-electron 24 exists in two isomeric forms; the ground state, which decays by e to the excited states of T1203 with a half—life of 52 h, and a 6.1—second isomeric state (Pb203m) at 825.1 keV. The study of 31203 thus becomes essentially a three—step process, the determination of the decay of Pb203, then Pb2°3m, and finally the B1203 decay. .l.2.6.A. Pb203 Decay Scheme Indeed, one would not be absolutely forced to study the szo3 decay scheme before studying the others, as the half-life is long enough to allow separation of its peaks from theirs on this basis alone. This, coupled with the realization that the decay scheme is fantas— tically simple (Figure 6) compared to the Bizou.205,206 schemes, led me to make no attempt to improve upon any previously reported data. The Pb203 isotOpe has been produced by a number of differ— ent reactions on T1203 and szou using protons, deuterons, and neu— trons [Pb53], or as a long-lived product of Pb2°3m and B1203 which can be prepared by yet other reactions. The experimental and theoretical characteristics of the decay have been well-established by a horde of investigations [St60,Pb53,Wa54,Wa58,Su61,Pr54,Va54,Pe60] utilizing a variety of experimental techniques. 14g,6.n. Pb7nlmwggggz The 6.1-s [£357] isomeric state at 825.! keV was first dis— covered by Hopkins [H052], who mistakenly assigned it to Pb202; in 1955, Fischer [F155] correctly reassigned it to Pb203 on the basis 0f excitation function studies. The next decade saw numerous inves— tigations [St60,Fr56,St56,Pe6l] on the Pb2°3m decay using primarily conversion-electron and NaI(T1) spectrometers. These studies report dolly tie-excited by keV (which is also ity was confined by that the 820.1—keV t can. thus mums the their work solv lured Iatrix element- Figure 6, along with 1.2.6.6. 3 Any coupr l77the fact that 3120 (:12 h). A simple we scribed later in sect. Pure am by keeping Wm) reaction (whicl at the required energ: other Bi isotopes, 11101 Ma rays of both 81“ aim a thorough inve: Several un be mentioned at this 25 a single transition of 825 keV from a l3/2+ state to the 5/2— Pb203 ground state, similar to other odd-mass Pb isomers. As the no reduced transition probability was abnormally large, Stockendal suggested [St60] that there is a likely possibility that the l3/2+ state is par— tially de—excited by an unobserved S-keV M2 to a 9/2— level at 820.1 keV (which is also populated in the a decay of 31203). This possibil— ity was confirmed by the work of R. Doebler et al.[Do68], who showed that the 820.1—keV transition is definitely present in the Pb2°3m de— cay, thus implying the presence of the S—keV transition. At the same time their work solved the difficulty of the abnormally large M4 re— duced matrix element. The present decay scheme for Pb2°3m is shown in Figure 6, along with the Pb203 decay scheme. Any comprehensive study of 31203 is necessarily complicated by the fact that 31203 and 31204 have nearly identical half-lives (:12 h). A simple method to prepare clean Bizo”sources (to be de- scribed later in section 2.1.) involves a (p,3n) reaction on nearly pure Pb206 by keeping the beam energy just below the threshold for the (p.4n) reaction (which produces the Bizoa); but Bizo3 sources prepared at the required energies invariably contain considerable amounts of B120”. Because there are so many other Bi isotopes, most tragically, gamma rays of both 31203 and B120”, the 31203 can be studied only after a thorough investigation of 3120” has been completed. Several unrelated characteristics of the B1703 decay should be mentioned at this point. The half—life of 31203, unlike the decay 680.! (I5) Fig. 6. 26 0.8 p‘s A N 9 row : °°o\° 8398 to 32 E 0.28 ns 3/2 203 8'TI Fig. 6. Pb2°3m [D068] and Pb203 [Pe60] Decay Schemes Mfluheavel listed in the litew mm, was. et I file 126.th state. 3120313 9/2, which where the 83rd pro trons are paired to With appr additional levels five neutron holes Would expect roughly 31201! ‘ Several in ”1:561, and Stockenda. conversion—electron a: game and electronrsi-lI these experiments are these experiments and “fa not complicated ‘ Positron emission, h" 9.74 MeV having been tensity is low, only 3W . What was p 27 itself, has been well investigated. Table 3 shows the half—life values listed in the literature to date. In addition to the half—life for B1203, Bergstrom et al. [Be61] have reported a half—life of 75i3 ns for the 126.4-keV state. The isotope has a small (1 part in 107) but mea— surable alpha branching, as was mentioned in section 1.1. Finally, atomic beam resonance has shown [L159] that the ground state spin of 31203 is 9/2, which agrees with the 9/2 spin found in B1205 and Bi207, where the 83rd proton is in the h9/2 shell model orbital and the neu— trons are paired to zero. With approximately [V166] 3.2 MeV of decay energy and the additional levels and collective behavior introduced because PbZO3 is five neutron holes away from the doubly closed shells of szoe, one would expect roughly the same complexity for the B1203 decay as for 3120”,. Several investigators, Novakov et a1. [N058], Fritsch [Fr56], and Stockendal [St60], have studied the B1203 decay using conversion—electron and scintillation spectrometers and by gamma— gamma and electronegamma coincidence experiments. The results of these experiments are discussed in Chapter III where the data from these experiments and the present work are compared. As if the decay were not complicated enough already, 31203 also decays partially by Positron emission, two 8+ groups with end-point energies of 1.34 and 0.74 MeV having been reported [Kr54]. Fortunately, the positron in~ tensity is low, only about 0.014 positions found for every 825.1—keV gamma . What was presented about the calculations for szO” might l________--IIiIIIIIIIIi_]IIIIIIIIIIIIIIIIIIIIII -.-—...— fable! Aleference [Pr58] bReference [NeSO] cReference [St56] dReference [St60] 28 Table 3. Experimental half—lives for 31203 decay Principal [31203 Investigator Half-life (h) Fritscha 11.5mm Neumannb ‘12.0il.0 Stockendalc 12 .310. 7 Stockendald 11.7610.05 aReference [Fr58] bReference [NeSO] cReference [St56] dReference [St60] Once 838 resolution Ge(Li) S m the 31203 decay any new levels and The meats made 1 ity of certain coin hold equally true f be regurgitated her The decay 31, indicate monume As good as they are. practical limit . Th for the very weak an has greatly improved vantes in detector 5 niques may show that and anomalies. In 1 rHis inves tigation I SPECtros copy . In additi several excellent rt 29 be repeated with added emphasis for Pb203. However, more exact calculations are not likely to be forthcoming until a better decay scheme and other experimental data are available. Perhaps the results of this thesis will prompt new, more detailed and comprehensive calculations on this isotope. Once again this investigation involved the use of high— resolution Ge(Li) spectroscopy singles and coincidence experiments, and the B1203 decay was found to be complex. With these techniques, many new levels and characteristics of 31203 have been uncovered. The comments made in the section on B120” decay concerning the valid— ity of certain coincidence experiments and the use of energy sums hold equally true for the B1203 decay as well and therefore will not be regurgitated here. V The decay schemes proposed in this thesis, Figures 22 and 31, indicate monumental changes from previously reported decay schemes. As good as they are, they have pressed the "state of the art" to its practical limit. The primary weakness lies in the coincidence data for the very weak and/or high energy transitions. Just as this work has greatly improved upon previous investigations, some day new ad- vances in detector systems, electronics, and computer analysis tech- niques may show that even this decay scheme has major inconsistencies and anomalies. In lieu of that day, the decay schemes produced by this investigation represent the ultimate in present day gamma—ray spectroscopy. In addition to the references cited in the review above, several excellent reviews of the lead—bismuth region should be noted here. Bergstrbn and hensive review attic] sitions in the Lead I on the lead isotopes. and Spectra of Heavy clei of lead and his: cussed the shell mode nuclei in their "The 30 here. Bergstrom and Andersson [Be6l] have published a very compre- hensive review article on "Nuclear Energy Levels and Multipole Tran— sitions in the Lead Region" which covers in more detail information on the lead isotopes. Kinsey [Kn57], in "Nuclear Reactions, Levels, and Spectra of Heavy Nucleit,has discussed energy levels in the nu— clei of lead and bismuth. Finally, Elliott and Lane [E157] have dis- cussed the shell model interpretations of the level systems of these nuclei in their "The Nuclear Shell Model". mm duction for 3120“ and B1203. Section 2 spectroscopy apparatus in curr Section 2.3. 31 The radioactive 312 dies of these nuclides werr mnhy protons and 383 hersources, however, were entities, raking accurate Merlin“ spectra nearly himsity sector-focused Cj mahvestigated to detem hthle. and beam energy r intuit free him source htelyhe avoided is 31203 hthat of him, thus mal bah-life differences. C that hi203 be either well sent at all in the 312°“ The reactions helm. Although the T1 hurled here for des crip 2.1. was Several sou 1205 1 .29.51T12°3) a, and“ 3 e 38 the projec 293 M and 312°“ fr a he3 on energy at 27-2 32 2.1. Source Preparation The radioactive 312°“ and 31203 sources used in previous shflies of these nuclides were prepared by bombarding szo6 and rmtural Tl by protons and He3, respectively, at a variety of energies. flmse sources, however, were highly contaminated with B1205’206’207 activities, making accurate energy and intensity calculations of the complex 312°” spectra nearly impossible. Using the Michigan State University sector—focused cyclotron [Bl6lL a number of reactions were investigated to determine the optimum target isotope, beam particle, and beam energy which would give the cleanest, most con— taminant free Bi20H source. The one contaminant which must abso— lutely be avoided is B1203, since its half—life is nearly identical to that of 8120” thus making it inseparable solely on the basis of 9 half—life differences. Consequently, any study of B1201+ requires that‘Bi203 be either well-known in advance or that it not be pre— sent at all in the Bizo1+ source. The reactions which were tested are listed and discussed below. Although the T1 attempts were nearly abortive,they are in- cluded here for descriptive completeness. 2.1.1. Tl Targets Several sources were prepared using both natural Tl (70.5% T1205, 29.5% T1203) and 99.9% T1203 separated isotope as the target and He3 as the projectile. Table 4 shows the Q values for preparing 81203 and 3120“ from the different reactions of He3 on T1. Choosing a He3 energy of 27-28 MeV,one would expect to produce B120” with r12°3(11e3.2")13i r12°3(ae3,3n)31 r12°5(ne3,6n)3i T12°5(He3,5")31 haw hlculated from experiment _ . ___.____ _.._._ —————_____ 33 Table 4; Q values for T1203’2°5(He3,xn) reactions W Reaction Q values (MeV)+ T12°3(He3,2n)312°‘* - 6.3 T12°3(He3,3n)B12°3 —13.3 T12°5(He3,4n)312°” —2o.5 T12°5(He3,5n)312°3 —27.5 W 1”Calculated from experimental masses listed in reference [My65], .‘rluuuof 31203 ft“ the f uphold be high enough 1 rites-all and thus produce hotly not the case, since hm, relatively large acti urltr the H51] laboratory l reactions may not be as cle; his, plus the present atte target source for 3120“ pro 2.1.2. Pb Targets The useable Biz h“ separated isotope 0b htloual Laboratory (in tl l unfroo the MSU cyclotrr diversity had chosen 27 ' rialues of the competing wit: errant amounts of 81205 34 a minimum of 31203 from the first reaction. It was hoped that this energy would be high enough to make the T1203(He3,3n) cross section quite small and thus produce little, if any, B1203. Such was ap- parently not the case, since the samples contained, in addition to 312°“, relatively large activities of Bi203, Bi205, and 31206. Other work in the MSU laboratory has also indicated that the He3—induced reactions may not be as clean as the proton—induced ones. Based upon this, plus the present attempts, the T1 was discarded as a possible target source for B120l+ production. 2.1.2. Pb Targets The useable B120” sources were prepared by bombarding 97.2% Pb206 separated isotope obtained from Isotopes Division, Oak Ridge National Laboratory (in the form of Pb(N03)2) with a 27-30 MeV proton beam from the MSU cyclotron. Previous experiments at Michigan State University had chosen 27 MeV as the best proton energy based upon the Q values of the competing reactions, but I found that at 27 MeV sig- nificant amounts of 31205 and B1206 were also produced, thus obscur— ing many of the high energy peaks (>1.00 MeV). Using Figure 7, which depicts the empirical cross sections for protons on szoe, I calcu— late that at :27 MeV abOut 437. of the radioactive source should be 131205, but if the proton energy is raised to 30 MeV only about 26% of the source should be B1205. The large difference in half—lives between B1205 and 8120“ make this (30 MeV protons) an excellent method to produce clean B120“ sources. Consequently, most sources b206 for this study were prepared by bombarding P separated isotope 2 z m m m R B MN 6 M. n. W .mzmqm. zoaqum MWOWU lO 35 N no a, (Shapiro) Pt)206 cross sections l" O ac(Shopiro) r°= L3 I I0"3cm caoss secno~ (BARNS) 8 2 8 8 5 S i 5 a; O PROTON ENERGY (MeV) Fig. 7. Excitation curves of Bell and Skarsgard [Be56] showing the measured (p,xn) cross sections of Pb206 as a function of proton energy. with 30 MeV protons- The useable 31 hrdiog97.21 rum (PMN tonbeal iron the MSU CYC for the Phloem“) react whim production) V81" slam in Figure 8 along ' work published by Bell a problem! on the basis chosen. it this energy thy are not significan hit since the photon en huh from the first pc the“ peaks from consic p202 1 (hence szozm) w 36 with 30 MeV protons. The useable B1203 sources were prepared similarly by bom— barding 97.2% Pb206 (Pb(N03)2) separated isotope with a 40—45 MeV pro- ton beam from the MSU cyclotron. In determining the optimum energy for the Pb2°6(p,4n) reaction, excitation functions (comparing B1203 to Bizoll production) were run on Pb206 from 30—40 MeV. This is shown in Figure 8 along with the equivalent excitation function from work published by Bell and Skarsgard [Be56]. The two are quite com- Parable,and on the basis of this a proton energy of :40 MeV was chosen. At this energy, while the 81205’206 impurities are seen, they are not significant. The unavoidable major impurity was Bizou, but since the photon energies and intensities for Bi20l+ were well— known fron the first portion of this study,it was easy to eliminate these peaks from consideration. In one run with 45 MeV protons some 31202 (hence szozm) was produced by the (p,5n) reaction, but this was not troublesome as most runs were performed with 40 MeV p. '. Typically several small crystals were crushed, bombarded With the 30-45 MeV protons at 21 uA for =1 1/2-2 hrs (often behind several mils of aluminum absorber), allowed to decay for 8—12 hours to let any short—lived contaminants decay away, and then counted for 3-5 half-lives, additional quantities of source being added with pass— ing time so as to keep a relatively constant counting rate. It was fOund that samples prepared and counted in this manner were relatively 6 ._ clean with small amounts of 31205 (t%=15.3 d) and Bi20 (t%-6.4 d) impurities. The B1206 impurities are seen weakly in the low energy PERCEI‘ IOO PERCENT Bi 203 .4 _ (I (fl (3 no (I PERCENT Bi 203 37 IN El 203. 204 MIXTURE + REFERENCE [Be 56] 30.0 32.5 35.0 37.5 Fig. 8. THIS WORK 40.0 42.5 PROJECTILE ENERGY (MeV , PROTONS) Curves showing percent 31203 in 3 Bi function of the projectile (proton) target. 203’20“ mixture as 3 energy on a szo6 38 region (<1 MeV), while the Bi205 is seen weakly in the high energy region (>1 MeV). In neither region was the impurity large enough to cause any undue problems in determining the 3120” or Bi2°3 full energy peaks. A chemical separation was found to be unnecessary, thereby making the preparation of the 3120” and B1203 radioactive sources a simple, easily handled process. fumd-ouauble u larger-sot, analyzers l mm, and more imam It this the the Labour luge confluent of Ge(L 1.9-keV (M1! at 1.33 Na “Ge(Li) detector tech: 1.2.1.8 In still The basic ca Ed in this study were a) two Ge( peratur and 1.? of 2.51 b) a room anvply c) a puls zero a “d d) a data No single c butwhen gamma ray en 39 2.2. The Gama-Ray Spectrometer Recent progress in gamma-ray detector technology, resulting in greatly improved Ge(Li) detectors (both in efficiency and resolu- tion), impressive performances in amplifier-preamplifier systems, faster and more stable analog—to—digital converters (ADC's),and larger memory analyzers has increased data accumulation of gamma-ray spectra, and more importantly, the quality of these data is improving. At this time the laboratory at MSU is impressively equipped with a large complement of Ge(Li) and Si(Li) detectors, culminating in a 3.6%, 1.9-keV (FWHM at 1.33 MeV) Ge(Li) detector, practically the ultimate in Ge(Li) detector technology. 2.2.1. Singles Egperiments The basic components of the gamma—ray singles Spectrometer used in this study were: a) two Ge(Li) detectors, cooled to liquid nitrogen tem— perature (77° K), possessing resolutions of 2.4 keV and 1.9 keV (FWHM at 1.33 MeV) and efficiencies of 2.5% and 3.6%, respectively, b) a room temperature FET preamplifier and high voltage suvply. c) a pulse shaping amplifier with DC offset and pole zero compensation, and d) a data read out system. No single component can be classified as the weakest link, but when gamma ray energies >2 MeV were measured, the number of .dmnebinthemm often blew): efficacy could oft: intensity and rays. In addi and all peaks within 10.! of counting rate no important broadened peaks due to long t1 humming rates can cause peak. Throughout the present for all singles game—ray ene 2.2.2. Coincidence Bari-en Singles experiment and intensities of the game- clides observed but tell one position of the nuclei invol‘ vealed in gamma-ray spectros: Eats. These include anti— tions), pronpt- (revealing c Musicians in cascade with 511-511-ga1mm- (revealing dc whcidence experiments. Tl fulneas to the present study 2.2.2.A. NaI('l‘l) One of the most ' nuclear spectroscopy labors ammlus. Reference [Au67] 0f the annulus vs. Ge(Li) E 40 channels in the MCA was often the weakest link. 0n the other hand, low detector efficiency could often fail to reveal full energy peaks of low Iintensity gamma rays. In addition, detector resolution may have ob— scured small peaks within $0.5 keV of larger peaks. A careful balance of counting rate was important since low counting rate can produce broadened peaks due to long term instability of the electronics, yet high counting rates can cause pulse pileup, which also broadens the peak. Throughout the present study these Ge(Li) detectors were used for all singles gamma-ray energy and intensity measurements. 2.2.2. Coincidence Experiments Singles experiments are useful in determining the energies and intensities of the gamma-ray transitions of the radioactive nu— clides observed but tell one nothing about the structure and com— position of the nuclei involved. This information is generally re— vealed in gamma-ray spectroscopy by a variety of coincidence experi~ ments. These include anti- (revealing direct, ground—state transi— tions), prompt— (revealing cascade transitions), delayed— (revealing transitions in cascade with states having a measurable lifetime), and Sll-511—gamma— (revealing double escape peaks and 8+ fed peaks) coincidence experiments. These coincidence techniques and their use— fulness to the present study are described in the following sections. 2.2.2.A. NaI(T1) Split Annulus-Ge(Li) Spectrometer One of the most useful pieces of apparatus in the MSU nuclear Spectrosc0py laboratory has been the 8"X8" NaI(Tl) split— annulus. Reference [Au67] suggests several useful applications 0f the annulus vs. Ge(Li) gamma—ray spectrometers. In the present who. Ifwhen a print-y two 511qu milintion phat till-5111mm coincidence Mid) detector, the relati photon (double escape peak) figuration it is possible t tensity of the double escap of these peaks and their 5 singles spectra. More will 2.2.2.3. Hulti One of the more laboratory, under the code iconputerized nultiparamel ventional coincidence expe1 from one of the Ge(Li) deto nuts are satisfied. Sepa for each individual peak 0 The conventional coinciden detectors, a collection oi the to assemble the appm No to the next was chang 41 study the 511—511—gamma triple coincidence configuration was found to be extremely useful in determining double escape peaks. The Ge(Li) gamma—ray detector and the radioactive sources were placed inside the annulus. If,when a primary photon interacts with the Ge(Li) detector, two SllekeV anniliation photons are able to escape collection, then each Sll-keV photon has a high probability of being collected by ei— ther side of the NaI(T1) annulus surrounding the detector. Requiring a Sll-Sll-gamma coincidence between the halves of the annulus and the Ge(Li) detector, the relative intensity of the weak (By—1022.0)—kev photon (double escape peak) in the spectra is increased. In this con- figuration it is possible to obtain significant increases in the in— tensity of the double escape peaks, thus allowing easy identification of these peaks and their subsequent removal from consideration in the Singles spectra. More will be said of this technique in Chapter III. 2.2.2.3. Multiparameter Ge(Li)-Ge(Li) Spectrometer One of the more useful techniques implemented at the MSU laboratory, under the code names EVENT and EVENT RECOVERY [Mi68], is a computerized multiparameter coincidence system. In the past, con— ventional coincidence experiments were performed by recording signals from one of the Ge(Li) detectors only if certain coincidence require~ ments are satisfied. Separate coincidence experiments were required for each individual peak or gate set on the pulse height analyzers. The conventional coincidence set—up required two NaI(Tl) or Ge(Li) detectors, a collection of associated electronics, and considerable time to assemble the apparatus. The only change necessary from one run to the next was changing the peak selected by the single channel pin height analyzer. For My. rays, this loam qflntmnhea the (to prel One nthod to pr: cation of efforts is to re: loving each and every fast I mlkeport (1969) of the NI tailed account of such a 3y: gm of the electronics and cidence events per second a emetic tapes as necessary Iillion events. Data tak type under the program EV was written in order to ex “P65, the sequence of Opel data typically being: 1) scan the ta] from each d 2) choose peak and 3) analyze the (noting the gain) . Applications 0 meter have greatly increa at Michigan State. In ad aPettrmneter used in this 42 pulse height analyzer. For the decay of Bizo”, for example, having >200 gamma rays, this would involve years of labor, computer, and 120” sources). cyclotron beam time (to prepare the many required B One method to prevent such massive duplication and rep— etition of efforts is to record the signals from both detectors fol- lowing each and every fast coincidence event. Reference to the An— nual Report (1969) of the Nuclear Chemistry group gives a more de— tailed account of such a system [Mc69]. Figure 9 shows a block dia— gram of the electronics and computer interfacing. Typically, 20 coin cidence events per second are recorded on as many 2400-foot, 9-track magnetic tapes as necessary until each tape is filled with about two million events. Data taking in this manner is controlled via tele— type under the program EVENT. A computer program, EVENT RECOVERY, was written in order to extract the coincidence spectra from the tapes, the sequence of operations for the recovery of this coincidence data typically being: 1) scan the tape for the integral coincidence spectrum from each detector, labeled X and Y respectively, 2) choose peak gates from one side, say X detector, and 3) analyze the resulting coincidence spectra (noting that each of these spectra has the same gain). Applications of this multiparameter coincidence spectro- meter have greatly increased the efficiency of decay scheme studies at Michigan State. In addition to the Ge(Li) multiparameter Spectrometer used in this investigation, future developments of this Fig. 9. Block diagr: nultiparsme‘ puter. LINEAR GAT E Fig. 9. 43 X-SIDE 8|92CHANNEL 8l92 CHANI‘EL Y-SDE ADC O-BV r Wmlfim‘Ifldfi- INTERFACE TO SIGMA 7 . ll - : CHANNEL NO, CHANNEL NO. OF EVENT OF EVENT FROM SIDE X FROM SIDE Y BUFFER IN SIGMA 7 [NDER I'JANUS" CHAMEL NO. CHANNEL NO, ONE WORD MAGNETIC TAPE CHANNEL N0. CHANNEL no or EVENT or EVENT . I/2 wont) ; s12 wono Block diagram of the electronics used for collecting multiparameter y-ray spectra with the Sigma—7 com— puter. iota-a! Ind-Ila triplex nu. Aposflpflity not p punter systen to study not radioactive species 0 In: the on one side and th mthe other, one could obt than-lived to moderate-11v Ieml desired. A previous line monitoring of total co rectal by allowing WRIT to whine language program us scattering experiments . Hi Present study would have ob 44 system may include triple—, anti—, and delayed-coincidence experi- ments. A possibility not previously proposed is to use this multi- parameter system to study widely different half-lives of many diff- erent radioactive species occurring in the same sample. By record— ing time on one side and the events from a single Ge(Li) detector on the other, one could obtain accurate half—life measurements for short—lived to moderate—lived components by gating on any time in— terval desired. A previous weakness of the system, difficult on- line monitoring of total coincidence events, has recently been cor— rected by allowing EVENT to run under TOOTSIE [Ba67], a two—dimensional machine language program used primarily for recording data from scattering experiments. Without this extremely powerful tool the present study would have obviously been impossible. luv: resulted in a vast inc Iiith this rapid increase in ysis has been nommental. tionvas perfomd on the puter utilizing FORTRAN pro Fanning is a brief but th energy and intensity measur Em coincidence spectra. 2.3.1. Gama Energy and 13 The centroids at Inn were found following 1 Matted backgrounds. The 4 0f two of the spectrum ans laboratory; MOIRAE (develo State University) and SAM? Of California, Berkeley). M SAHPO is a com] W I. Routti and adapted ‘ T. Arnette and C. Merritt scope and switches and/ or 45 2.3. Data Analysis The rapid advances in experimental nuclear spectroscopy such as precise, high energy cyclotrons for source production, bet— ter resolution in Ge(Li) detectors, and large multichannel analyzers, have resulted in a vast increase in the rate of data acquisition. With this rapid increase in data accumulation.the task of data anal— ysis has been monumental. Most of the data analysis in this investiga— tion was performed on the MSU cyclotron laboratory XDS Sigma—7 com- puter utilizing FORTRAN programs written or adapted for it [Mc70]. Following is a brief but thorough discussion of the gamma-ray energy and intensity measurements, and the analysis of the gamma— gamma coincidence spectra. 2.3.1. Gamma Energy and Intensity Measurements The centroids and areas of the photon peaks in a spec— trum were found following the subtraction of various order inter— polated backgrounds. The computations were performed with the aid of two of the spectrum analysis routines used in the MSU cyclotron laboratory; MOIRAE (developed by R. Au and G. Berzins at Michigan State University) and SAMPO (developed by J. Routti at University of California, Berkeley). 2.3.1.A. SAMPO Spectrum Analysis Routine SAMPO is a computerized data analysis routine written by J. Routti and adapted to the Sigma—7 MSU cyclotron computer by T. Arnette and C. Merritt. Control may be maintained either via a scape and switches and/or FORTRAN control cards. Solenfdlevnriednau of 1) to produce c 2) to calculate 3) to calculate on 4) to calculate At present this thatis without scope contr wolves an initial shape par analyzed. Strong, well—res calibration. The program i of the peak and leading and peak. The shape parameters used to get the parameters Once the shape parameters l mu, they may be reread 611 for subsequent runs, thereI tiontines. Once the shap energy calibration may be to linear or higher order Similarly, efficiency calib her of well-spaced peaks 8 The actual anal who hm basic nodes: 1) autot out ‘ uate 46 Some of the varied uses of SAMPO ARE: 1) to produce Calcomp or printer plots of the spectrum, 2) to calculate centroids, and consequently energies, 3) to calculate areas and relative intensities, and 4) to calculate half-life data. .At present this routine is utilized as a separate program, that is without scope control. SAMPO's mathematical evaluation in— volves an initial shape parameter calibration over the region to be analyzed. Strong, well—resolved singlet peaks should be used in this calibration. The program fits a Gaussian curve to the upper portion of the peak and leading and trailing exponentials to the base of the peak. The shape parameters are stored and a linear interpolation used to get the parameters for any other peak under consideration. Once the shape parameters have been calculated for any given spec— trum,they may be reread directly into the program via control cards for subsequent runs, thereby considerably shortening future calcula— tion times. Once the shape calibration has been established, the energy calibration may be calculated. The energy values may be fit to linear or higher order polynomials at the Operator's discretion. Similarly,efficiency calibrations may be made by specifying a numr ber of well-spaced peaks and their corrected relative intensities. The actual analysis portion of SAMPO may be performed under two basic modes: V 1) automatic - in which SAMPO subroutines search out all statistically significant peaks, eval— uate suitable fitting intervals, and fit the ! 1 peak u calibr m1 2) contra preset locati the fi scribe Figure 10 shows Peaks, with the following i 1) exact cent} 2) energy (any 3) area-count and I.) intensity— Because of othe laboratory.SAMPO has only foremost advantage found t to strip multiplets in can all the possible multiplei viously required to strip of the usefulness of the the 212-222—keV quartet s was stripped by indicatin the approximate center cl dots are actual data poi! the *‘s are points where is (mite excellent. For 47 peak using the shape, energy, and efficiency calibration data. and 2) controlled — in which the operator directly prescribes a fitting interval, the number and location of peaks to be found in that interval, the fitting then being made under these pre— scribed conditions. Figure 10 shows a sample output of a fitted quartet of peaks, with the following values being returned for each peak: 1) exact centroid (and error) 2) energy (and error) 3) area—counts (and error in percent) and 4) intensity—counts (and error in percent). Because of other excellent data analysis routines in our laboratory.SAMPO has only recently been put to much advantage. The foremost advantage found to date has been in reducing time required to strip multiplets in complex Spectra. SAMPO allows one to strip all the possible multiplets in a single Spectrum in the time pre- viously required to strip a single multiplet by hand. An example of the usefulness of the program is seen in Figure 10, depicting 1201+ the 212—222~keV quartet seen in the B spectrum. The quartet was stripped by indicating the end points used for background and the approximate center channel of each peak in the multiplet. The dots are actual data points, the +‘s are SAMPO fitted points, and the *'s are points where the two are identical. Note that the fit is quite excellent. For a set of 4 separate B120” runs the energy mm 3!? '0‘ u 00“ 050:0: 000050050 3353' E33333?” gm Fifi!!!“ 3!! 3 0 33.3 3333. 331."! 60° 0°... 0° OO‘OOS ~7- z. u an - n'i "tram i: "on” one ooooooooooao flute.— not-comma. Ifittfltho “Mei?“ «3.3%»..50513 can uuuuuuuuuuuuuu 333533333333 .3333? Fig. 10. Photograph analysis rt The fit is 3120”. 48 n27? oMNOoN 0000.0 moowmknooo tuna.“ mooumhnooo mama...» nowoé nun—.mnw "no-.. 2. nulunu~wmnmc 32: 886 3.33.6 not; outlast; 8:.” #2.... $33.; 2.?" R3 2. name :7 2.3 Bruno—uh. anon.» . oooa.o no.uos.~.o no...“ no.uoso~.o 3.”..0 soo..o sass.~s~ ons~.o "an. an. ... oLu :2 IR ...;fluium unnamwnhvz uo-cau-aqu 53339.32. on a J - ... x u ml: $51.. 3 «U.Su 3230 15!. 573”...“ 5.35.3... 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I .3 .il gilto-s .2), no.unns.o no.usus.o . ao.uns.o ..o. .sa. .o.uuas.o .o.uaqs.o . no.u.n.o ..o. ..u. 2:09 :3 c -3 . . I I I? an ..i l- I ,3 | 00000500 oofll '0‘. no.us...o no.u.ns.o .. no.uns.o .... .... . . mooufih-o Col! can. 80002.0 00053.0 :3 |.~U:=~:::=:::::::::_:—::~:—:::~:::-:=~ has» (bde §Kna°~ no uhuuauuuukuuuh—T—k:::—_::n=:: gomnnfi, - o The fit is to a 212—222—keV quartet from the decay of analysis routine SAHPO, as run‘On the Sigma-7 computer. B12013 Photograph of line-printer output from the Spectrum Fig. 10. v ' meter the manual foreachpeakand the int Once the data have been e1 fro- an on-line data acqu type of display, log or 1' flea, and various compute P18) 0f a portion of the at the top gives channel be: of counts in that cha Play. the run number, the 0f the background fit bei the display, the Compton 1 Sales in Figures 12 and ‘ background determined by The sense switches are us of points in the spectrum abort lines indicate the for the background calcu] 0!lesions of points can 133110119 the result of 91 ”riginal spectrum. From “Ether to use the full 49 range for the individual peaks in the quartet was about 0.35 keV for each peak and the intensity range within 11%. 2.3.1.8. MOIRAE Spectrum Analysis Routine MOIRAE, the backbone of the MSU nuclear spectroscopy data analysis system is a FORTRAN program that utilizes a Fairchild 737A live-display scope and sense switches to perform the spectrum analysis. Once the data have been either read in from cards or transferred from an on—line data acquisition program, the switches control the type of display, log or linear, the expansion and shifting of the axes, and various computation routines. Figure 11 shows the dis— play of a portion of the BiZOL+ gamma—ray spectrum. The information at the top gives channel position of the long pointer and the num— ber of counts in that channel, the number of cycles in the log dis- play, the run number, the subroutine presently in use, and the order of the background fit being used. The Compton edge in the center of the display, the Compton of the 375—keV peak, is shown on expanded scales in Figures 12 and 13. In Figure 13, a 4th order fit to the background determined by the set of background points is shown. The sense switches are used to move the tall pointer to the position 0f points in the spectrum used to calculate the background. The short lines indicate the position of points that have been accepted for the background calculation. Either a set of individual points or regions of points can be used to calculate the background. Figure 13 shows the result of subtracting the background, along with the original spectrum. From this one selects the peak limits, and Whether to use the full raw peak or the portion of the peak with .wouomuunsm smomumww .gHoZ Emumoum ofiu wfisoumxumwnwmwwmmm ASH some: can mm .5930on has .3 .wfim so open powMMMowmououumsv on“ was . . .mam. m MW Nwmwmsofia mo dowuuom Goon uni.” mafia: HE House . .ma I sawdunv 3:33 we mmammwn me . .w oncomojuwowo .Ha .wfim Lindon. m mo 33> wwwcmmxm NH ...H w i “U ' A" ’- Uh E 7 1‘ o 1525 3 5959 ..-~ amt! greater than nus-flu hmflmflnfls the mud, with: square root mkedoneuda, printed, Once m the necasary anal the mute: (under the coe lion curve using a least—ac calculate the relative inn Naturally, each distinct advantages and di ful since it allows imedi abackground order, backg etc. SAMPO, on the other able to fit multiplet peak unable to do. Conversely, (Second) background fit, r insome regions of the Sp! mm}! has the added diam for hours at a time. To ‘ R. Firestone are presentl FOP-9 computer so that it 2.3.1.C. Game The gamma—ray Wins a least-squares < troid channel numbers of cWilputiug the energies o 51 counts greater than one—third maximum to calculate the centroid. 1d. The program then finds the centroid, area, sum of raw data and back— ground, and the square root of that sum. This information can be punched on cards, printed, and/or plotted on a Calcomp plotter. Once all the necessary analyses are accumulated, one can have the computer (under the code name MOIRAE E(I)) calculate a calibra— tion curve using a least-squares fit to a quadratic equation and calculate the relative intensities from the areas of the peaks. Naturally, each of these routines, SAMPO and MOIRAE, has distinct advantages and disadvantages. MOIRAE is particularly use— ful since it allows immediate operator control over such parameters as background order, background points and interval, peak end points, etc. SAMPO, on the other hand, has the distinct advantage of being able to fit multiplet peaks accurately, which MOIRAE is presently unable to do. Conversely, SAMPO is handicapped by a low order (second) background fit, making it difficult to fit peaks accurately in some regions of the spectrum, most notably near a Compton edge. MOIRAE has the added disadvantage of tying up the live—display scope for hours at a time. To alleviate this difficulty, G. Giesler and R4 Firestone are presently adapting these analysis programs for a PDP-9 computer so that it can perform the same functions as MOIRAE. 2.3.1.C. Gamma-Ray Energy and Intensity Measurements The gamma-ray energy measurements were performed by com— puting a least—squares quadratic calibration equation from the cen— troid channel numbers of well—known standard gamma—rays and then Computing the energies of "unknown" gammas from the centroids and -thestannard centre. The on ‘htenll' energy calibrati in themheovn and stands: The choice of ti aphyleut are mortal": ft Ideally one would like eta: bungee-a, which emit on‘ We, and which have a sun distribution night othervi one Inst balance these req ulibration points in orde utve. The game-ray r the use of a detector effi angles from :100 to 3000 i log of the ith full euerg: Photon energy (31;) between detector. The dependence Computer program which ca sities form the punched )1 areas from 3—6 runs on ea final relative intensitie the MOIRAE E(I) program. 13.2. Double and Singlt The detectors dent that single escape 52 the standard curve. The energy calibration curves were made from "internal" energy calibration spectra taken by simultaneously count— ing the unknown and standard calibration sources. The choice of the standard calibration sources and their employment are important factors in the gamma energy calibrations. Ideally one would like standards which closely "bracket" each un— known gamma, which emit only the gamma rays actually used as stan— dards, and which have a small number of them since their spectral distribution might otherwise obscure photons of interest. However, one must balance these requirements against the need for many good calibration points in order to establish a reliable calibration curve. The gamma—ray relative intensities were established through the use of a detector efficiency versus gamma energy curve for en- ergies from =100 to 3000 keV. A linear relationship between the log of the ith full energy peak (effi) and the log of the ith photon energy (Ei) between 2400 and 3000 keV was observed for each detector. The dependence was incorporated into the MOIRAE E(I) computer program which calculates the energies and relative inten- sities form the punched MOIRAE cards. In this work the relative areas from 3—6 runs on each of Bi‘203’20L+ were averaged and then the final relative intensities were calculated from these areas using the MOIRAE E(I) program. 2.3.2. Double and Single Escape Peaks The detectors used in this study were sufficiently effi- cient that single escape peaks, peaks differing from full—energy pahhyfilhhmno mdmleesespepesks vet penks). nedouble escape the full energy peak, were expert-en: as described en cape peaks. These double tbeenergies of the full a used since recent evidena fereneee need to be correa based upon the detector-en the detector produced by In: effect" is small [Gu being used for energy cal detecting double and sing Edges, but since these pe sbectm are so "cluttered my useable method. .233. Gamma-Gamma Coinc In all coincic 00W multiparameter sy: cidence" events and peak 1) true coi 2) backseat 3) chance 6 b) cascade peak wh‘ 53 peaks by 511 keV, were so small that they were undetectable (i.e. no single escape peaks were found for any of the higher intensity peaks). The double escape peaks, having energies 1022.0 keV below the full energy peak, were detectable. A 511—511-gamma coincidence experiment as described earlier was used to determine the double es- cape peaks. These double escape peaks were also useful in checking the energies of the full energy peaks. However, care must be exer— cised since recent evidence [Gu68] has suggested that the energy dif— ferences need to be corrected by a "field increment effect" factor based upon the detector—source geometry and the electric field in the detector produced by the diode bias voltage. This "field incre- ment effect" is small [Gu68],so it was ignored, the pair—peaks not being used for energy calibrations anyway. An additional method of detecting double and single escape peaks is their lack of Compton edges, but since these peaks are very small and the B1203 and B1204 spectra are so "cluttered" with many peaks,this is definitely not a very useable method. 2.3.3. Gamma—Gamma Coincidence Spectra In all coincidence spectra recovered from the EVENT RE- COVERY multiparameter system there are several sources of the "coin— cidence" events and peaks: 1) true coincidence events (and peaks), 2) backscatter events (and peaks), 3) chance events (and peaks), and 4) cascade events (and peaks) in coincidence with a peak whose Compton lies under the gated region. éhonlytheflnt (1) 196: mountain: there“. A diifimltiesincoincidenca [E69370]. In these ref: detector configuration is . shield each detector fro- at the one the. Both (2 siting on regions median high sides of the peak. 11 these lultiparaneter coina subtract immediately weigh thengnetic tape is scam fective technique will be 54 As only the first (1) is desired,one must do his best to avoid or compensate for the rest. An excellent discussion of backseattering difficulties in coincidence studies has been presented by G. Giesler [Mc69,Gi70]. In these references he shows that a 90° Ge(Li)-Ge(Li) detector configuration is optimum, using a graded lead absorber to shield each detector from the other without absorbing the gamma rays at the same time. Both (2) and (3) can be determined or removed by gating on regions immediately adjacent to the peak, on both low and high sides of the peak. In the EVENT RECOVERY program (used to scan these multiparameter coincidence magnetic tapes) it is possible to subtract immediately weighted spectra taken with adjacent gates as the magnetic tape is scanned. Several examples of this highly ef— fective technique will be illustrated in Chapter III. 23.1. DEA! 5mm Pro The constmcti followed relatively stand line the great difficul unusual characteristics b plexity introduced by an rays. In the present inv spins, and purities of th intensities, and the log construct a decay scheme individual decay. The 10 hymn-coincidence data, data, delayed-coincidence laces or other parameters this becomes progressivel Once the state Ema transition intensil by a simple (but tedious: written a FORTRAN comput Under the code name DECA done. I found that a I! each tine it was to be i ative beta feeding to e: blaring gama rays, an 55 ‘2.4. 'DeCay Scheme ConstruCtion 2.4.1. DECAY SCHEME Program The construction of the decay schemes in this thesis have followed relatively standard procedures for decay scheme production, since the great difficulty in these schemes does not lie in their unusual characteristics but rather simply because of the great com— plexity introduced by an inordinately large number of weak gamma rays. In the present investigation the results include the energies, spins, and parities of the states, the gamma-transition energies and intensities, and the log ft values to each state. The methods used to construct a decay scheme are varied and invariably tailored to each individual decay. The location of states can be initially suggested by anti-coincidence data, gamma—energy sums, prompt—coincidence data, delayed-coincidence data, and gamma—ray relative intensity bal— ances or other parameters, but as the number of gamma rays increase this becomes progressively more difficult. Once the states are determined, however, the beta and gamma transition intensities and the log ft values can be determined by a simple (but tedious) sequence of Operations. D. Beery has written a FORTRAN computer program, described in reference [Be69], under the code name DECAY SCHEME which does these routine calcula— tions. I found that a major disadvantage of this program was that each time it was to be employed one must calculate the total rel— ative beta feeding to each state due to the populating and depop- Blating gamma rays, an inconvenience when one is dealing with 25 " dime states. the prey: uebof the hon states htedfrucardinpot data nip.tbelevel itpop conversion coefficient (if rehtive beta feeding calc brim than depopulating state, the relative beta to zero,and the calculati saved my an hour of lab ful in a number of other description of DECAY S {3669] since it gives a the to give here. “.2. TAKE CARE Program During any dec Oneself taking numerous c and other well—known stat transitions that might co 0f gamma transitions (an not seen unusually tedic 200 and the levels excec mental. Much to my our] Which alleviated this P the derivation of the n 56 or more states. The program was consequently modified so that for each of the known states the total relative beta feeding is calcur lated from card input data. For each well—placed gamma ray, its energy, the level it populates and the level it depopulates, and its conversion coefficient (if knowu) are input and the resulting total relative beta feeding calculated. If a state has a greater popu— lating than depopulating intensity, a warning flag is output for that state, the relative beta feeding (difference in intensities) is set to zero,and the calculation continued. This minor modification has saved many an hour of labor and exasperation and has been very help— ful in a number of other large decay scheme constructions. For a description of DECAY SCHEME it would be worthwhile to see reference [3669] since it gives a more complete description than I have taken time to give here. 2.4.2. TAKE CARE Program During any decay scheme preparation one invariably finds oneself taking numerous energy differences between a preposed state and other well-known states hoping to find additional justifying transitions that might confirm that proposed state. When the number 0f gamma transitions (and hence energy stateS) is limited this does not seem unusually tedious,but when the number of transitions exceeds 200 and the levels exceed 25, as they do in szou, it becomes monu— mental. Much to my surprise no program was found in this laboratory which alleviated this problem. Therefore, TAKE CARE (see [Cr70] for the derivation of the name) was written to fill this obvious gap. T" .‘ y a" 'hlpite of its child the ham gem rays. and ate in either or both of M, all the energy dif and mated to the tolerance set by the con illustrated in Figure 14 the more useful option 1 existing decay scheme by fit, to within some spec level and the existing 1 arbitrary level and fin considered as transition energy levels. Figure 1 PM from the 312°“ study 3am rays are not necee the tolerances alluded 1 regions, one for the 0— the >1500-keV region. While this 1: Points up another impo: rays. Many of the gem: 0f possible transition Samoa rays , placement 57 In spite of its simplicity, it has been of nearly invaluable help in construction of the complex 312°” and B1203 decay schemes. The input parameters consist of the knowu energy levels, the energies of all the known gamma rays, and control parameters. The program can oper— ate in either or both of two modes, TAKE and/or CARE. In the routine TAKE, all the energy differences between known levels are calculated and compared to the known list of gammas, and any that match within a tolerance set by the control cards are output in a convenient form, illustrated in Figure 14. In the second mode of operation, CARE, the more useful Option is excercised, that is, one may "scan" up the existing decay scheme by l—keV intervals to find those gammas which fit, to within some specifiable tolerance, between the "scanning" level and the existing levels. In this manner one may look at any arbitrary level and find out what known gammas are possibly to be considered as transitions between the unknown level and the known energy levels. Figure 15 shows a portion of the CARE program out— put from the Bizo1+ study. Since the errors in the energies of the gamma rays are not necessarily uniform over the entire energy range, the tolerances alluded to above can be set independently for two regions, one for the O-lSOO-keV region and a separate tolerance for the >1500-keV region. While this program is simple (yet very useful), it also Points up another important aspect of decays involving many gamma rays. Many of the gamma rays appear to be involved in a multitude 0f possible transitions, thus indicating that, for a large number of gamma rays, placement of levels solely upon precise energy sums is a jg] (tocuii .1.th 3.3.: 00.0 no.0 , 00.0 00.0 , 00.0 8.0 0000 no.ammm 00.0 wm.momm 0000 hnofihmm 00.0 mwomwmm “UH-.flM?BN NMUONM.~N 00.0 wh.hnmm G‘IHRNMUIORWWUJ “flohflm timNm>uJ :B.s«s« 00.0 00.0 00.0 00.0 om.ooom 00.0 00.0 mau0ham mmumwmm NM-EM‘N ONOkflmu JU>MJ 00.0 mm.nam« no.0 00.0 no.0 on.fimwa «n.0mmfl 00.0 no.0 00.0 00.0 00-330N oo.«osm om.mmom o:.monm om.:dmm om.ommm om.mswm on.mnmn oo.mmmm mm.0m0: ON.O$N: Jlm>NJ The —h A portion of t CARE program. ray energies the energy 18 within a spec ence between in the left studies. Fig. 14. 58 cm.mnma sh.omms 00.0 00.0 00.0 00.0 00.0 00.0 00.0 m..Hmum 00.0 00.0.00 om>uo mm.moma ha 00.0 ms.moo mm.mwm 00.0 00.0 00.0 oh.Hom 00.0 0N.mmo mn.omo 00.0 mo.mmw 00.0 00.0 00.0 00.0 om.oo:a 00.0 md.noofi oo.mmofi mm.mooH 00.0 00.0 00.0 mm.Hmmm mm.momm hm.mnmm mw.mamm mm.mm:m sh.hdmm mm.cwon 40.04 00.nfixa Ma 00.0 0m.wfim nm.m.m 00.0 00.0 00.0 00.0 00.0 00.0 00.0 .m.0:: 00.0 00.0 00.0 00.00HH nm.aHHH :A.HHNH 00.:nmfi mm.mmmH 00.0 sn.sfisfi 00.0 00.0 00.0 00.0 mm.moom 00.0 00.0 mm.on«m mm.momm mm.mm:m Jm>mo 0a mmn printer output from the TAKE A portion of the TAKE routine line— Fig. 14. in keV) and gamma- “ decay scheme The energy levels (on the left as (in keV) are from the present Bi £0 The nonzero energies in the 4 columns to the right of gamma rays whose energies are ble tolerance (here 1 keV) of the energy differs l (e.g. "LEVEL 1944.60") and the levels the energy levels correspond to within a specifia ence between the tested leve in the left—hand column. CARE program. ray energi studies. Illllddddlllll‘quWWJ - «0.903 3.002 00.0 «3.32 00.002 00.0 00.0 ... .00. 0...... 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.2 . m . a . wmum oono 00.0 00.0 00.0 00.0 00.0 00.0 . www.msm mm; 00:30 , 00.0 Maw-won" 00.0.03 3.0.03 00.0 3.003 00.003 00.00.“; 00.0 00.0 00.0000 00.0 00.0 wmnw wmnw oo.o mfmwmd 3.33 9.00.0; 00.0 00.0 00.0.00 00.0 00.0 00.0 o o oo.o 00.0 00.0 00.0 00.0 00.0 00.030 00.0 00.0 00.0 omno oono 00.0 00.0 00.0 00.0 00.0 00.0000 85 8.. 00.0.: we“... “we... 00 00 M0... 000" OOuhINN 00. 0 - ”NM 000thN OOIOWNN OOommNN 00.:mmm oo.mmNN ooummmm 00.0mmm oo.ommm JL)UJ OOODWNN MIL. UZnFmUk 59 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 “0.000. 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 OOCmMNN oohwmmm 00 00.0 00.0 00.000 00.0 00.0.. 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.000 «m.m¢m mm.Hoo 00.000 am.finn 00.000 .0..0m 00.0 00.0 00.0000 00.000. 00.0 00.0 00.00m0 00.0 00.0 00.0 00.0 00.0 m" 00.0 00.0 wo.mwm oo.o :m.o:¢ 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.00m «0.030 mm.fioo 00.000 «0.000 00.000 :m.aHm nn.wmm 00.0 :w.momH 00.0 00.0 00.0 m«.momfl 00.0 00.0 00.0 00.0 00.0 a 00.0 00.0 00.0 00.0 00.000 00.0 00.0 00.0 00.0 00.0 00.0 00.0 mn.mmm 00.0 00.000 00.0 00.0 00.0 00.0 nn.wmm 00.0 00.0 mo.mmmH 00.0 00.0 m«.moma 00.0 00.0 00.0 00.0 00.0 \I H 00.0 00.0 00.0 00.0 0:.wm¢ 00.0 00.0 00.0 00.0 00.0 00.0 00.0 mH.mmm 00.0 m¢.moo 00.0 00.0 00.0 00.0 00.0 00.0 00.0 mc.mme 00.0 00.0 00.0 00.0 00.0 00.0 mm.omwd 00.0 o 00.0 00.0 m¢.mnm mh.0mo 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 om.mmm 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 ow.mnmd m¢.mwma 00.0 00.0 mm.omwa 00.0 m mo.Hmmm mo.ammm mo.ammm n o mm.mmmH mm.mmmfi ma.«mMa m:.mnm mn.omm 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 om.mmm 00.0 00.0 00.0 00.0 00.0 00.0 m:.mnm 00.0 00.0 00.0 00.0 ow.mnmfi m¢.mwmfi 00.0 00.0 mm.ommfi oo.o 00.ummm.oo.0mmm 00.0m00 oo..mmm 00.0000 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.000 00.0 m..mnm 00.0 00.0 mm.nfimfl 00.0 ow.mnmfi m:.mwmfi 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.H¢w om.w«m mm.¢om 00.0 00.0 00.0 mm.hama 00.0 00.0 00.0 00.0 00.0 00.0 00.0 m mm4 00.0mmm 00.0 0m.mmm 00.000“ mw.mom« 00.0000 00.3.00 oc.moom mm.mmdm oo.ommm m:.:mmm 00.0mmm om.mwmm nm.nn¢m 00.000m 00.0000 0m.mmmm 00.0mom 00.mmom 00.00am 00.0Hmm 00.mmmm 00.0osm 00.0000 00.0000 0m.¢fiwm 0m.omwm 0m.m.wm 00.mnmm oo.mmmm 00.000. om.omm¢ m1» Olmhmm» utine line-printer output from The energy levels and gamma— the Bi20H decay scheme studies. A portion of the CARE ro the TAKE CARE program. ray energies are from Fig. 15. not so surprising that rectly placed during the TAKE CARE program (includ numerical calculations . onDBCtape, and run under into core via an appropfi Elana were written by R- Iore complete discussion Parameters can be found 1 1) ARITH - c 2) INTER - i tensitie: interest 3) PLYFT — 4) ICC - us internal 60 risky if not poor practice. This is well indicated by comparing the decay schemes of this investigation (Figures 22 and 31) with the pre— viously published decay schemes (Figures 17 and 27, respectively), where many levels were based solely upon precise energy sums. It is not so surprising that many of these levels were shown to be incor- rectly placed during the present study. A computer listing of the TAKE CARE program (including ample comment cards) can be found in Appendix A. 2.4.3. Auxiliary Programs The PDP-9 computer in the Nuclear Chemistry group labor- atory has been indispensable for excellent data acquisition, but in addition it has proven very useful for performing routine types of numerical calculations. The programs are written in FORTRAN, stored on DECtape, and run under a keyboard monitor system. Each is brought into core via an appropriate teletype command. Most of these pro— grams were written by R. Eppley of the Nuclear Chemistry group; a more complete discussion of each program and the necessary input parameters can be found in reference [Mc69]. 1) ARITH — desk top calculator type program, 2) INTEN — calculates and renormalizes gamma-ray in- tensities from efficiency curves of the detector of interest, 3) PLYFT — a general least—squares program, 4) ICC — used for interpolation of the theoretical internal conversion coefficients from other routine calculations and be nde here. 61 published tables, 5) TRIGA - calculates the expected activity of samples submitted to the MSU TRIGA reactor, and .6) BLACKJACK - just that, the computer plays the operator via teletype, for those moments when it looks as if mother nature is against you, In the experimental section of this thesis these programs will not always be mentioned by name but they were often used for routine calculations and consequently some mention of them should be made here. 2.5 Asluenredeol began to conpile this the! and effort that no soon I coincidence spectra taken coincidence oyste- deactil require plotting the data beiing each peak of inter: finished page of plots. ‘ the Celcomp 565 plotter, entire spectra, including labels. Searching the co astonished to find none t deficit, two plotting tor VALTAVA and COINPLOT. Er tail below (with listings 2.5.1. Program VALTAVA Just as TAKE ‘ Program for decay scheme (though simple) answer t deed, the name VALTAVA i new listing of the in Appendix B. The data hip to make the program tOC are, in order: 62 2.5. Plotting Routines As I neared completion of the B1203’20” projects and began to compile this thesis, I became painfully aware of the time and effort that was soon to be spent in the preparation of many coincidence spectra taken using the Ge(Li)-Ge(Li) multiparameter coincidence system described in section 2.2.2.3. Each spectrum would require plotting the data (in India ink), titling each spectrun, 1a— beling each peak of interest, and finally blocking and titling each finished page of plots. The obvious solution, of course, was to let the Calcomp 565 plotter, interfaced with the Sigma—7 computer, do the entire spectra, including the titles, borders, and peak energy labels. Searching the computer library for Such a program, I was astonished to find none that was satisfactory. Remedying this deficit, two plotting routines were written under the code names VALTAVA and COINPLOT. Each of these programs is decsribed in de- tail below (with listings in the Appendices). 2.5.1. Program VALTAVA Just as TAKE CARE is a fantastically simple but efficient program for decay scheme work, so VALTAVA is'a highly powerful (though simple) answer to our time—consuming drafting problems. (In— deed, the name VALTAVA is Finnish in origin, meaning "powerful".) A FORTRAN listing of the program (with comment cards) can be found in Appendix B. The data input was kept as simple as feasible so as not to make the program too unwieldly or narrow in scape. These cards are, in order: 1n. and It) a NARI card vidual spec Given these input control line about the bounds of line at SOD-channel inte Wt tick marks on the or mark, and finally label Program will automatical] from 100 counts full seal “M the magnitude of the care was taken such that Mad, even partially. laPlains of the lettering will adjust (space) then this program can be four 25.2. Program common Program COIN! idea to reduce drastica 63 l) the title card (containing the desired title for the plot), 2) the crunched data deck (compressed data format, al— though any data input could be easily adapted to the ,program), 3) the cards used to label the peaks (one card for each peak, containing the approximate centroid and the energy of the peak), and 4) a MARK card (billboard card) to separate the indi- vidual spectra. Given these input control cards,the program will (in order) draw a line about the bounds of the entire plot, put tick marks on the base line at SOC—channel intervals, put on the title, plot the spectra, put tick marks on the ordinate and the number of counts at each mark, and finally label each peak with the apprOpriate energy. The. program will automatically scale the spectra in a base 10 log plot from 100 counts full scale to 1 million counts full scale,depending upon the magnitude of the largest peak in the spectrum. In addition, care was taken such that two energy labels could never be superim— posed, even partially. If two centroids are given such that over— lapping of the lettering would occur,the program senses this and will adjust (Space) them prOperly. A sample plot as produced by this program can be found in Figure 21. 2.5.2. Program COINPLOT Program COINPLOT was actually born out of VALTAVA and an idea to reduce drastically preparation time of coincidence plots. deck (def mi 4) the start lower lef Given this input, COINPLO imlly scale the N spectr secutively. Once again ( plot from 1 to 6 cycles ( each spectrum, and put tic does not plot the charact done later with a typewri tan be done with the ball leasy India ink. Even sc fit of coincidence plots rt“Wired. Without a doul than by (conservatively) dttafled comment cards c Perhaps, I ha than it really is. On t 64 The input for the program is fantastically simple, a single control card and standard crunch punch data decks. The data input on the control card includes: 1) the size the final plots are to occupy (in inches) on an 8 %" x 11" page, 2) the number of spectra (N) to be placed in the above area, 3) the number of channels to be plotted from the data deck (default = 4096), and 4) the starting position of the first plot from the lower left hand corner of the page. Given this input, COINPLOT will outline an 8%" x 11" page, automat— ically scale the N spectra for the allowed Space, and plot them con— secutively. Once again (as in VALTAVA) it will scale each individual plot from 1 to 6 cycles (common logx based upon the largest peak in each spectrum,and put tick marks on each axis. Unlike VALTAVA,it does not plot the characters or label the individual peaks; this is done later with a typewriter. The beauty of this is that the plots can be done with the ballpoint Calcomp pen rather than using the messy India ink. Even so, this was found to yield a good—looking set of coincidence plots at a fraction of cost and labor previously required. Without a doubt this program cut down figure preparation time by (conservatively) at least three weeks. A listing containing detailed comment cards can be found in Appendix C. Perhaps, I have made this program seem more sophisticated than it really is. On the other hand, simple as it may be, it has which“ hidingdhprogrlds ultytnexpressabitofl laboratories and/or publil outputs in published saw fomtion uploaion, has 4 dear physics data that m in such publications , neat lterisl for publication 4 ml as VALTAVA and COM direction. 65 saved literally weeks of work both for the draftsman as well as my- self, and as such it certainly deserves mention in this thesis. A sample plot can be seen in either the 3120” or 31203 coincidence Spectra sections found in Chapter III. An additional reason for including this program description is that it gives me an opportu- nity to express a bit of personal philosophy. In the past, certain laboratories and/or publishers have frowned upon the use of computer outputs in published material. The past decade, with the vast in— formation explosion, has seen such an increase in particle and nu— clear physics data that unless computer output is freely permitted in such publications, nearly as much time will be spent in preparing material for publication as in doing fundamental research. Programs such as VALTAVA and COINPLOT are, I believe, a step in the right direction. 3.1. Electn 3.1.1. Introduction is discussed i aunier of nuclear react of energies on szotnzoe hill-purity separated isc bean energies, the previ( had to be content with 81 “205,206,207 impurities piex iii201+ spectrum diff initial attempts utilize meters having energy res While both yielded excel (<1000 keV), at the same to most conversion—elem efficients for low mult: many conversion electro 1 transition reported u only 1140 keV. Using 1 concluded that: the dec: from the existing ener [StSSI , while reaching CHAPTER III EXPERIMENTAL RESULTS 3.1. Electron Capture Decay Scheme of BiZOF 3.1.1. Introduction As discussed in section 2.1., B120l+ has been produced by a number of nuclear reactions involving protons and He3 at a variety of energies on Pb204:206 and T1 isotopes, respectively. Lacking high-purity separated isotOpe targets and high—resolution cyclotron beam energies, the previous studies [Fr56,St58] of the BiZOL+ decay had to be content with sources which were highly contaminated with B1205’206’207 impurities, making an accurate analysis of the com— plex B120L+ spectrum difficult, if not impossible. Both of these initial attempts utilized high—resolution permanent—magnet spectro— meters having energy resolutions of 0.1% [St58] and 0.2% [Fr56]. While both yielded excellent results in the low energy region (<1000 keV), at the same time each suffered the limitation common to most conversion—electron spectroscopy, i.e. the conversion co— efficients for low multipole transitions are just too small for many conversion electrons above 1000 keV to be seen. The highest Y transition reported using conversion—electron spectroscopy was only 1140 keV. Using these electron results,Fritsch et al. [Fr58] concluded that the decay scheme was too complex to be constructed from the existing energy and coincidence data. Stockendal et al. [St58], while reaching essentially the same conclusion, did publish 66 Since the lee alllel and the high tel, one certainly would populated by the new" d cent advances in Ge(Li) felt that a re-investiga Sane 210 y rays were ide viously reported. Utili wsmany of these were 1? level scheme for szo“ . 3.1.2. Source Preparati The M2014: soc riched isotope Pb206 (as sector—focused cyclotrox a production were previc lived contaminants were nus times following the sides of the peaks. L allowing the samples to rEmilining impurity peak these sources . 67 a tentative decay scheme but at the same time emphasized that the only levels and transitions known with complete certainty were the szoum levels and y rays. Since the decay energy for Bizol1t has been estimated [Fr56] as 4.4 MeV and the highest previously reported level is at 2478 keV, one certainly would expect to find many states above 2500 keV pOpulated by the B120“ decay. For this reason and because of re- cent advances in Ge(Li) spectroscopy not formerly available, it was felt that a re—investigation of the BiZOH decay might be worthwhile. Some 210 y rays were identified, this being some 143 more than pre— viously reported. Utilizing the multiparameter coincidence appara— tus,many of these were fitted into a radically changed and improved level scheme for Pb20”. 3.1.2. Source Preparation The Bizou sources were prepared by bombarding 97.2% enr riched isotope Pb206 (as Pb(N03)2) with 30 MeV protons from the MSU sector-focused cyclotron for 1-2 h at 1-2 uA. The details of such a production were previously discussed in section 2.1.2. Short- lived contaminants were determined by counting the samples at vari- ous times following the bombardment and noting variations in inten- sities of the peaks. Long-lived contaminants were revealed by allowing the samples to decay for 3—7 days, then determining the remaining impurity peaks. No chemical separations were performed on these sources. 3.1.34. Sin 1 A Ge(Li) detect :cryoatat, was used to dete We rays. Typically. Wat 1.33 MeV, using a noise RC linear amplifier and a 4096-channe1 analyze mated with 3" x 3" Na1( distance of 10 centimeters wanted, was used to confi Tnis detector had a resolu efficiency. The y-ray energ Member of well-known calib larger peaks were first de Simeltaneously with these M was determined by eit 3.3.1.8.) spectrum analysi lit to a least—square nth the calibration curve. Tl to determine the energies iheir centroids. The fine iften obscured by the sta Boswell—known stronger Y Sizileer method. The inte 68 3.1.3. Bizoq'l—ray Spectra 3.1.3.A. Singles Spectra A Ge(Li) detector, mounted in a right angle dip—stick cryostat, was used to determine the energies and intensities of the B120“ Y rays. Typically, the resolution ranged from 2.25 to 2.5 keV FWHM at 1.33 MeV, using a room temperature FET preamplifier, a low- noise RC linear amplifier with DC offset and pole—zero compensation, and a 4096—channe1 analyzer. This detector had an efficiency of 2.5% compared with 3" x 3" NaI(T1) detector, using a source-to—detector distance of 10 centimeters (cm). A second Ge(Li) detector, similarly mounted, was used to confirm the energy values of the observed Y rays. This detector had a resolution of 2.0 keV FWHM at 1.33 MeV and a 3.6% efficiency. The y—ray energies were determined by comparison with a number of welleknown calibration sources, listed in Table 5. The larger peaks were first determined by counting the Bi201+ sources simultaneously with these standards. The centroid of each standard peak was determined by either SAMPO or MOIRAE (sections 2.3.1.A. and 2.3.1.B.) spectrum analysis routines, the centroids of the peaks being th fit to a least—square n (n=2 commonly) degree curve, which became the calibration curve. The calibration curve was then used, in turn, ~201+ to determine the energies of the larger unknown Bi peaks from their centroidS. The energies of the weak Bizo” Y rays, which are often obscured by the standards, were finally determined by using the now well-known stronger y rays as internal standards, and applying a Similar method. The internal standards of B1201+ used in this study halide Talfll CEISS SCHG 69 Table 5. Y rays used as energy standards for the B120“203 decays. W Nuclide y—ray energy (keV) Reference W Ta182 100.104:0.ooz a 152.435:0.003 156.387i0.003 (D a 179.393:o.004 a 264.072:0.009 a Ce139 165.84i0.03 b Sc“6 889.18i0.10 c 1120.41:o.1o c 31207 569.63i0.003 d MnS“ 834.83i0.04 e,f c5137 661.632:0.069 g Co60 1173.23:0.04 e 1332.49ao.04 Co56 846.782i0.060 1037.85110.060 ll75.085i0.070 1238.290i0.040 1360.219i0.040 1576.56li0.050 1771.33:0.060 2015.33i0.07 2034.90:0.06 2180.1710.07 2231.6010.06 2251.1510.07 2429.28:0.lO 2598.52:0.05 3009.9:0.10 D‘P‘hi'hV-hi'ht'ht'hi'hl'hhhl’hi'hl'ht'hf'hm n2“ 14,203 y“ hiermce [Gr-65] Ilefereuce [Ge65] cReference [Ra67] leference [142157] EReference [H368] lieference [@168] 3Reference [Wh67] hReference [Au67a] 1Used in the 81203 calibre Table 5. (continued) 3202.18:0.07 f T1208 583.139i0.023 e 2614.47i0.10 e Pb2°3 279.17:0.02 d,i Y88 1836.13t0.04 e,f aReference [Gr65] bReference [Ge65] cReference [Ra67] dReference [Ma57] eReference [M368] fReference [Gu68] gReference [Wh67] hReference [Au67a] 70 1Used in the 31203 calibration only. hector is shown in Figure vrlnrily used on the 312°“ reason that it was not pure Iental work was completed. A list of the en trays resulting from the c‘ assigned energies are the n taken at varied times and : Ge(Li) detectors. The cor were: the major calibrati the 0-1000~keV region, :0. £0.25; and in the 2000-30 The relative p iron several runs, the st: biting much larger than th Of course. Those peaks in keV transition) have unce leaving intensities <11 he frenely small intensity The relative photopeak e the 2.5% detector were 1 Estandard set of y—ray “Ell-known. The result miter program, which 3 immediately from the I 71 are shown in Table 6. A y—ray spectrum of B1204 taken with the 2.5% detector is shown in Figure 16. The 3.6% Ge(Li) detector was not primarily used on the Bi201+ decay for the simple but understandable 20H reason that it was not purchased until nearly all the Bi experi- mental work was completed. A list of the energies and relative intensities of the y rays resulting from the decay of Bi20g is given in Table 7. The assigned energies are the mean values for 4—6 different measurements taken at varied times and amplifier gains and with each of the two Ge(Li) detectors. The corresponding uncertainties in the energies were: the major calibration peaks, i0.10 keV; the remaining peaks in the 0-1000—keV region, $0.15 keV; in the 1000—2000 keV region, $0.25; and in the 2000—3000—keV region, i0.5 keV. The relative peak intensities listed are also averages from several runs, the statistical uncertainties in the intensities being much larger than the uncertainties in the energy determinations, Of course. Those peaks having intensities >1Z (relative to the 899.2— keV transition) have uncertainties ranging from iS—lSX; the peaks haVing intensities . Q: Q ° 3225‘ _,_ D \— § c csaex as: a W— 00) N z 7242— *O 9 999?.— a «71— Q 50992/ 6'zcuf I 999a— :' ”ll—— 2 zen-x _. z 9001— g rasca— 1. Star—- a use—— it 066—» 9 Guz— o res-f 1 0902— 9 '96—- E “oz—— ”‘6‘. 8 9 awe—— z als\ J R 9 nos-— 2 see—— (.... a): 3::\ come»- 80’9\ b 7.11.). " o 0 Egg'\ 9 m 42,— wee-Q v (sed— ---s— I I“ f 9 7922/ (mien soar 7- z '61 _, I 17.2\ § 9 9‘91 -— '1 N :35: 6 991—- 9 cu/ . 7 9:1/ 9“":— 2 self Call/f 9601/ a 69 U) 1819-” o 9 oz LL] 9 cssf a 9:02: 3 £2; § 9 6002— \l .1 Q.) a £69\ N a: 52212 2 2.22:” W~ \ s 926!— (I) g 99g\ 8 1.06!— 1 C.‘\ c 9691’ £532— .. e 9991—— (mteu 919:; 99291\ g a 109 o z 9791.‘ _ r can N g :3: e 1. g 9 9n: _\ or o»\ — (mm): v9u-\ m s an} cgslcful— l. x 25:: hflr$$> 7 “f 1 9017/ 1mm: I 6'.‘H— . U 44'“ -— _/ (...-nu tvc—- 4 @3953- lle\ 0"“ A 109-: 0 IZE— 4 8 v secl— ' l6£\ 5 arm—— 9 693/ s: m .m\ gm; 9 ()ng g “6’ Z 22 -\ a 99m 9 g‘zZz— , 99w) 1. 9 2'2 9 lvn—f‘ 2 9U"\. L VIM—— 9 591’ 6 vstf “ § Z L?!’ C {(C9— . e ow/ 3i???— ‘ ' z ech/ lqsz v08 spa 900— ‘ “’x r. - ‘ I~q—=:§EEEEE§§“ “m\ 1 / 7 sgzn—\ 9 a O 0927\ a 2:21—— . u ' L ”le 1_ amen—'- cn-‘ N. .4. e 1 ‘ ‘ 7 ' ' . — - . " ' ' o - 9 (g 0 ,0 X x r, X x v _ u, . 4. m “ TBNNVHO/SlNflOD CHANNEL NUMBER 2250 2330 1500 ing a um taken with a 2.5% Ge(Li) detector hav 4 keV FWHM (at 1.33 MeV) in this run. BiZO” singles y—ray spectr resolution of 2. Fig. 16. Table 7. Energies present Measured y-ray Rea energy (keV) In \— 80.40 96.54 100.74 109.38 140.80 147.36 164.92 169.83 176.17 212.70 216.11 219.46 222.15 227.46 240.40 248.91 74 Table 7. Energies and relative intensities of Y rays present in the e decay of B120”. Measured y—ray Relative Measured y-ray Relative energy(keV) Intensity energy (keV) Intensity 10k 1 (continued) ____———-————— 690.75 709.13 710.48 718.43 725.15 736.07 745.23 753.78 765.37 771.31 791.16 821.13 823.05 827.62 831.95 834.10 841.06 847,16 899.15 911.74 911.96 918,25 924,16 934.13 950,33 958.77 964.32 Table 7. (continued) 690. 709. 710. 718. 725. 736. 745. 753. 765. 771. 791. .13 .05 821 823 827. 831. 834. 841. .16 899. 911. 911. 918. 924. .13 950. 958. .32 979. .98 990. .19 .93 847 934 964 983 1014 1021 75 13 48 43 15 07 23 78 37 31 16 62 95 10 06 15 74 96 26 16 33 77 45 34 OOHOOOOU’OOI—‘OOOOI—‘l—‘O Ill H H H H c o H u: c DOOOOO '_| .91 .44 .42 .86 .97 .70 .74 .03 .50 .39 .39 .61 .52 .51 .94 .02 .25 .90 .00 .39 .40 .67 .07 .36 .16 .19 .53 .35 58. .12 .08 .19 44 75 1027.59 1037.34 1043.63 1049.04 1056.55 1060.17 1064.22 1092.10 1095.08 1102.18 1111.27 1127.50 1132.89 1139.77 1146.54 1157.66 1167.01 1181.24 1198.98 1203.84 1211.74 1232.92 1259.08 1261.71 1274.81 1290.61 1299.21 1328.22 1334.53 1347.93 1351.13 1353.35 0.07 0.39 1.38 0.20 0.18 0.52 0.99 0.10 0.21 0.60 1.62 0.28 0.87 0.63 0.18 0.60 0.22 0.07 0.24 2.09 3.25 0.46 0.44 0.14 2.79 0.20 0.12 0.39 0.31 0.23 ,0.47 0.87 Table 7. (continued) W— 1380.01 1383.62 1414.74 1446.12 1447.52 1466.36 1468.82 1475.08 1487.78 1517.53 1524.05 1536.54 1569,19 1572.86 1589.45 -607_19 -612.15 1639.33 1645.62 1652.00 1654.87 1669.23 475.07 1685.37 168912 1700.14 303.32 76 Table 7. (continued) 1373.68 1755.29 1380.01 0.22 1760.97 0.20 1383.62 0.16 1778.49 0.28 1414.74 1.00 1780.33 0.34 1446.12 0.09 1796.91 0.11 1447.52 0.22 1803.95 0.06 1466.36' 0.36 1818.18 0.53 1468.82 0.39 1826.55 0.57 1475.08 0.09 1836.59 0.07 1487.78 0.21 1851.00 0.09 1517.53 0.36 1856.86 0.27 1524.05 0.86 1881.76 0.34 1536.54 0.42 ; 1896.31 1.38 1569.19 0.14 1907.23 0.17 1572.86 0.23 1916.43 0.05 1589.45 0.32 1925.87 0.60 1607.19 0.21 1941.27 0.84 1612.15 0.13 1956.74 0.40 1639.38 0.34 1958.10 0.42 1645.62 0.61 1964.77 0.39 1652.00 0.57 1988.00 0.03 1654.87 0.57 2009.56 0.08 1669.28 0.10 2014.09 0.05 1675.07 0.08 2028.24 0.14 1685.87 0.15 2045.99 0.08 1689.12 0.60 2064.19 0.03 1700.14 0.26 2084.22 0.04 1703.32 2.09 2092.56 0.04 1709.85 0.10 2100.62 0.05 1715.22 0.14 2137.57 0-03 1731.53 0.66 1 2169.44 0.04 1749.82 0.29 i 2172.21 0-03 Table 7. (continued) WET-'— 2183.68 2251.63 2263.38 2279.37 2312.39 2325.95 2433.32 2450.72 2472.58 2475.63 2517.74 2566.14 2655.12 2668.24 2680.93 X 77 Table 7. (continued) _ 2176.93 0.05 2686.82 0.31 2183.68 0.03 2721.15 0.03 2251.63 0.04 2758.80 0.10 2263.38 0.31 2765.26 0.02 2279.37 0.04 2794.38 0.02 2312.89 0.07 2802.07 0.02 2325.95 _ 0.04 2837.33 0.25 2433.32 0.03 2854.92 0.02 2450.72 0.05 2864.65 0.01 2472.58 0.04 2898.01 0.01 2475.63 0.03 2947.99 0.01 2517.74 0.21 2955.55 0.02 2566.14 0.10 2976.89 0.02 2655.12 0.05 1 2990.49 <0.01 2668.24 0.02 3011.36 0.03 2680.93 0.38 3062.99 <0.01 An anti-coinci are not in cascades (or ‘ ground-state transitions. necessarily a panacea to transitions. The fact t1 that the transition does deed, it may be in 8 str a1 ray in an "anti" E othery's, or that it gc Consider a y ray feeding coincidence experiment . 934% Sequence has been . 1‘ ray is enhanced, it 1 0.011. Thus, in spite 0 not accept that Y rav a hon without further ve In the 8130‘“ 899.210) state (Figun 31 ray which is not 11 that perhaps an " 1150 anti" , the highest 1743 keV. ' ThlSY ray in 03 state would vield a t . 8 tin 319d decay energy ( stat es 0 directly p01 78 3.1.3.3. Anti-coincidence Spectra An anti—coincidence Spectrum reveals those Y rays which are not in cascades (or very weakly so) and are primarily e—fed ground—state transitions. Caution! An "anti" experiment is not necessarily a panacea to the elucidation of all direct ground—state transitions. The fact that a Y ray is not enhanced does not mean that the transition does not directly populate the ground state; in- deed, it may be in a strong cascade. Conversely, the enhancement of a Y ray in an "anti" does not mean that it is not in cascade with other Y's, or that it goes directly to the ground state. For example, consider a Y ray feeding a long—lived metastable state. In an anti— coincidence experiment this Y ray will be enhanced because the cas— cade sequence has been effectively broken; even though the populating Y ray is enhanced, it is most definitely not a ground—state transi— tion. Thus, in spite of the fact that a peak is enhanced,one should not accept that Y ray as a direct, non—cascade ground—state transi— tion without further verification. In the B120” decay all Y—ray cascades pass through the 899.2—keV state (Figure 17), thus ruling out any possibility of having a Y ray which is not in cascade with another and suggesting that perhaps an "anti" for the 31204 would not be greatly beneficial. Also, the highest Y—ray energy recorded during this study was 3063 keV. This Y ray in cascade with the 899.2 keV of the first excited state would yield a state at 3962 keV, which is approaching the es— timated decay energy of 4.4 MeV. However, if any of the high energy states do directly populate the ground state, then one might expect EFF? Pr.» 2 v C. 9 ll 6 7» m.» 0.. 9 W. 7' I. s a “VJ-V 11“ 0W0 0“ .000 .64 ..m USE—10W \CQUUQ W30.) 10.9149 'ONI w .mwmuma 33.5 How mamaom hmumt wfinumucou twwoaoum hamsofi/ona 95 .HH .wwm VONDQ O 40 ....m .mmo .N 4186 3K _ .2 c. ... WI? II. w a _ .0 ~89 9 as . - w: m-w-ml ...... ImnnnnnI-n . . .4. 1.3 .w Emma Mama .. Ilnlnnu -m 1.11 1.11%... 2L8 . . . ... vo~_m wEonm tame £53me 235. +0 to see more high energy Y‘ sideration of the spins a support for the argument The ground state of 81207 seats [1058] ) and consec Pbm” would be expected 1 the ground state of Pb”1 direct population from t‘: arguments an anti-coinci Specialized exception wi M A most inforn escape spectrum was take 80 to see more high energy Y-ray transitions >3 MeV. Finally, a con— sideration of the spins and parities of Bi204 and szou lends final support for the argument against an anti—coincidence experiment. The ground state of Bi201+ is 6+ (determined by atomic beam experi— ments [J058] ) and consequently the high—lying populated states of Pb20l+ would be expected to be primarily 5+, 6+, or 7+ states. As the ground state of Pb207 is 0+, it would be quite unusual to find direct population from the high—lying states. Based upon these arguments an anti-coincidence experiment was deemed unnecessary. A Specialized exception will be discussed in section 3.1.4.F. 3.1.3.C. Double Escape Coincidence Spectra A most informative but also very time—consuming double escape spectrum was taken early in the investigation using the NaI(T1) split annulus (section 2.2.2.A.). A block diagram of the necessary electronics and experimental set—up is depicted in Figure 18. Re— quiring a 511-511—Y triple-coincidence between the separate halves of the annulus and the Ge(Li) detector, one finds that the double escape peaks are greatly enhanced in the resulting spectrum. The spectra were calibrated both externally and internally, as well as by using a self—gated singles spectrum. A great problem ensues in trying to obtain enough counts to gain reasonably good statistics in the spectrum. While the experiment lasted nearly a week, gain shifts caused most troublesome difficulties. Figure 19 is such a double escape spectrum, with only the double escape peaks being noted. However, not all the peaks seen in the double escape spectrum are seen in the singles spectrum; only some 11 peaks were actually r------__-- Km.k.n_lv¢< “(N—(.4 tu—k.4lz( “(mz.|- m Hie.” oznzhlhl Auva~‘z .opoa :Hucm: ofi nfi we 92% noon: 9.3 was some 033 mum m.ox13m 05 do waaow 32053 map um£u zoom voumdhum mum m.¢omH osu Esuuoomw oocwwflocfloo >IHHmIHHm m Mom .muuoomw moaovfioawoo A» IHHmIHHmV wamowo waasow was Ifiucm wcwwuooou How asuom Hmuuofiwnoaxm 1:29.» ¢<4mn 03 0 ll wt; .2qu «4(205 ukwz mm.H um zmsmv >mx q usonm mo coausaommu m wflwwm: Houuwumw Afigvmw co m m wfim msasadm ufiamm AHHvaz wSu auHB uoxmu aduuuwmm manomw vacuow :o Hm .mH .wH N. .m mmmEDz szze'esé— $9132— Lu )6 ‘f . (\ B O gh'SZI-- 2 N O No fio D 2 ~ WENNVHO 83d Sanbo Fig. 21. Two coincidence spectra (from the B1203 decay) illus— trating the effectiveness of background subtraction in the EVENT RECOVERY program. (The spectra were prepared using the VALTAVA plotting routine described in section 2.5.1.) peakeontains a 800d P0rt Compton edges. Bath 1847 strong coincidence with t hi y ray appears strong] one were not aware of th:‘ "false" coincidence data Sections 3.1m 0f the szomoa level 5 coincidence plots which Study. All the coincide pared using the versatil KN GATE." indicates that label "XXXX-KEV GATE WI'] been subtracted. Final‘ 88 peak contains a good portion of the strong 1847.6— and 1893.3—keV Compton edges. Both 1847.6— and 1893.3—keV transitions are in very strong coincidence with the 820.2-keV y ray; consequently, the 820.2- keV Y ray appears strongly in the 1507-keV coincidence Spectrum. If one were not aware of this problem, he could easily be misled by the "false" coincidence data. Sections 3.1.4. and 3.2.4., which deal with the construction of the szou,203 level schemes, contain most of the PbZOL+ and Pb203 coincidence plots which have been recovered during the course of this study. All the coincidence plots found in these sections were pre— pared using the versatile plotting routine, COINPLOT. A label, "XXXX— KEV GATE" indicates that_ng background has been subtracted, while a label "XXXX—KEV GATE WITH BKGD SBTD" specifies that background has been subtracted. Finally, a label such as "XXXX—KEV BKGD ONLY" specifies a spectrum of the background 23ly_for the XXXX—keV peak. Almost all peaks were recovered with and without background subtrac— tion but space limitations preclude including all of them. One last word might be helpful: while all of the coincidence spectra are in— cluded, not all will necessarily be referred to explicitly but are included for completeness sake and in hopes that they may facilitate future investigations of these isotopes. 3.1.3.E. Delayed—coincidence Experiments Only one long-lived state (in addition to szogm) has been previously reported [SuSO]. This is the 1274—keV state, with a t% of 260 ns. The prompt—coincidence experimental apparatus had a resolving time of :100 ns. Based upon this resolving time and a ti of 260 ns 2 for the 127cm state, 1 coincidence spectra are 3692 are chance. The ch enough, and the renainin spectrum. Consequently, was performed. If there certainly going to miss coincidence experiment, 80 these. As will be 5. intensity has been plac state will not substant 3.1.4. Construction of Figure 22 st love ‘ 20“ ls 111 Pb as into 89 for the 1274—keV state, =31% of the counts in the 375—keV prompt— coincidence spectra are true, real coincidence events; the remaining 269% are chance. The chance events can then be accounted for easily enough, and the remaining spectrum is the same as a delayedficoincidence Spectrum. Consequently, no separate delayed—coincidence experiment was performed. If there are other delayed states present,then I am certainly going to miss them by not performing an anti— or delayed— coincidence experiment, but time considerations require that I fore- go these. As will be seen in section 3.1.4., >90% of the BiZOL+ decay intensity has been placed in this study and any remaining delayed state will not substantially alter the present data. 3.1.4. Construction of the PbZOLf Level Scheme Figure 22 shows schematically the e decay of Bi20” to levels in PbZO” as interpreted from my data. These 30 excited states and 60 y—ray transitions were placed utilizing primarily y—ray singles and coincidence data, aided by energy sums and intensity balances. This section consists of the specific evidence and the logic used to 20'+_ arrive at this decay scheme for Bi Before dashing headlong into 20” "decay scheme logic", however, let an involved discussion of the Bi me take this brief moment to clarify the purpose of this section. The preparation of a complicated decay scheme does not follow, as I may have erroneously implied, a hard and fast set of logical steps. Rather, one attempts to assimilate as much experimental data as humanly feasible and then allow these data to gestate or in~ cubate until a pattern, seed, or idea seems to blossom and grow. There is no, as I rapidly discovered, "easy" way to construct a level GILZh 204 B. 6. \D O 0 E ONV'Q fin) n_u3u>mcg K)". Na) “EN. —_ w.) [T V: @Nh'w mfiufifiwgye'fico fits ,;,; ...m v~ q, a) v A l A I - A 323239 AWAAAA AA 32 .- 32 “ mmvs‘amazae 1‘ $8 at ,2... an A v ““5999": mansio- “29 "3V. “3 '35,": :5 g d” ée°e°°°°3~wweo 3:: 2m 302ch :' o (.0 to N (I) . V ‘- n a? a! N v ' in _ ' . (D a) (D t g 2 g 0 ' -‘ co '2 2‘ m (O'OO|)Z‘668 33 (L‘ELM'ULQ (DL'Z)Z'692 fl (IB'OW'ESSIn II- (L'OI)€'806m “’9 °’°"°‘ln'l-I- (“TRIM-III- 3 229Imma- (”TIMING-w ‘6°'Z"‘°”---u-- (V'B§)0'b96 (EI‘ODB'OZE (ZQ'OD'EZB-n (LO‘UZ'Sllm I . (66'0)Z‘ZZZ In'l V0'Z)6‘8b2 ' “WW-M I“ ‘Gfl’9‘99—n- ‘z°'°’a'z°"_III----n (l9‘0)9'9b9|_ ”"2"“ ml".- lL'OlM'OLS m- | (as-noun. ...- (mbupm . I ‘29‘°’3'm—I_n- (vacuum mm-I_llI-I-- v - — ‘°"°’°“°°-—_u 0 ‘zz"’”‘°--I_I N (BL‘ZW‘DLZI _Q m-omss _II (os-on'Lc-e: 07v «emu -II . (U'II)O'ZI6 .. I (OL‘OH'SSL II (menace :::::= “"""9°°‘ —' -== “°’°""""I - —I --- (QG'OXTZGSI _ ‘95'°"°“I -r.'- .- ‘66‘°"""' I -I_ -- (W‘OH'BSSI'I- - ...... "IIII (Etnl'SOL . (SB'OW‘BM =I ‘°°'z’°“°" I-l— ‘°"°""‘“ I-l— E'°'Z""°"I—I --l— ‘°"°’°'""I_I — ‘°°'°’°"“'I -l—I ‘“'°’°"“'I I-I_I (ea-mo'oett I I .- (m'mg'mzm -l— -- (Iron-€923 ' '_' -I— -- mom...“ a I _I (tome-3m I I—ll -I— -- (ac-om... I I—II -l_ —- oz-on-mz ll I—I II-I_ -- (ea-omen _l I--I— .- (OE ole 9892 IIIIIIII_II-I--I_I r1 ‘ “ “ I a . o Hewett: to are. A , metht‘oaomthwmwbwlow 0‘0 «7"‘9 ,m'“ ‘7 0 <1 N ‘Nuuuuu ...-.1. ... ‘lv'"'n v “nmnmhmfifimnn‘chnvbé mm V “"n F18. 22. The f. decay scheme of 151m" proposed by the present, study. AiJ transitions were placed using coincidence data alone, without scbne. Consequently’ t1 which I present in this the method by which the does, however, give any such placements as I hav deletions more understar Before returr look momentarily at the is not a "typical“ deca' Foremost, inasmuch as t 0+, respectively, one u ground state, as this s Indeed then, everything 899-2-keV first excitec is aptly Seen in the B: at this spectrum one s mm“ only some 30 of l in transition. This ad ' ' 0 1ntens1ty calibrat ana ' lyzed this causes it u . ratively). Because! i than been exceeding' d my Scheme from th e 91 scheme. Consequently, the sequence of steps ("decay scheme logic") which I present in this section, does not represent, even remotely, the method by which the initial decay scheme was constructed. It does, however, give any future investigations the final reasons for such placements as I have made, thereby making future assignments or deletions more understandable in light of my present decay scheme. Before returning to the level assignments, I also want to look momentarily at the peculiarities of the BiZOL+ decay. Indeed, it is not a "typical" decay at all (though I defy making such a definition). Foremost, inasmuch as the ground states of B1204 and szoLl are 6+ and 0+, respectively, one would expect no direct feeding to the PbZOL+ ground state, as this would have to be a "super"—forbidden transition. Indeed then, everything (i.e.,all y—ray cascades) passes through the 899.2—keV first excited state. The most insidious difficulty, though, is aptly seen in the BiZOL+ y—ray singles spectrum (Figure 16). Looking at this spectrum one should note that there are very few strong transi— tions: only some 30 of the 210 y rays have intensities >1Z of the 899.2- keV transition. This presents no inordinate difficulty for the energy and intensity calibrations, but when y—Y coincidence spectra are being analyzed this causes monumental headaches (literally as well as fig— uratively). Because the majority (385%) of the B1201+ y rays are-200 Y rays. transitions and level: energy suns but suff i ahigh degree of conf vith these additional Without further evidv certainty, but the e: additional transitio transitions for whic bva semicircle at t Placed solely on the of the diagram are 5 with may feed the by using the my; C through the alreadv be "locked" in by 5 States 110 these transitions account for :90% of the decay, one is not so con— cerned about the absolute number of Y rays assigned. The 60 Y rays placed in this section represent only those which can be placed pri- marily upon coincidence data, energy sums being somewhat risky when one has >200 Y rays. During the course of this study many other transitions and levels were suggested by the coincidence data and energy sums but Sufficient evidence was lacking to place these with a high degree of confidence. Figure 25 shows a decay scheme for Bi204 with these additional Y rays and excited energy states included. Without further evidence these cannot be placed with unqualified certainty, but the existing evidence seems to indicate that these additional transitions and levels may exist. The placement of those transitions for which there is some coincidence evidence are denoted by a semicircle at the base of the transition, while the rest are placed solely on the basis of energy sums. On the right hand side of the diagram are some possible levels and their associated Y rays which may feed the 2185.4—keV isomeric state. These were obtained by using the TAKE CARE program to scan up the existing decay scheme through the already known states and searching for levels which might be ”locked" in by several Y's between the 2185.4—keV and remaining states. While not necessarily adequate, this may lead to states which do indeed feed the 2185.4—keV level. No separate calculations (e.g. external quantum number assignments, and log ft's) will be made for these levels, although one might wish to do so at some later date. Fig. 24. The Y The 5 data takin Spec: Fig. 111 24. The Y—Y coincidence spectra from the B120]+ decay. The spectra were recovered from the coincidence data stored on magnetic tapes using EVENT data— taking routine. Sample titles of the coincidence spectra and their meanings are found below: lOO—KEV GATE: A gated region from which background has not been sub— tracted; lOO—KEV GATE WITH BKGD SBTD: A gated region from which background has been subtracted; lOO—KEV BKGD ONLY: Spectrum of the back— ground adjacent to the 100— keV gated region. Unless otherwise specified, all spectra are dis- played from the X axis. JWZZ(._U WuNWL WLVZ‘JOU 112 m l i _ m 100-KEV GATE WITH BKGD SBTD 140-KEV GATE WITH BKGD SBTD ‘i Plllllm I III. 1 3 I l I“ all“! llu m T 1 l 102 szz315, I 102. JIM—226$. .0 KER WIPZ‘JOU COUNTS PER CHANNEL 122 01.0“ 1‘. ND «,2- 438-440-KEV GATE WITH BKGD SBTD I a: I: o“ g; 0 O NN m [\m oo o I II ‘.I “if A'I I 101 1 438-KEV GATE WITH BKGD SBTD 2 N 10 0 I\ N 4.0 - um I\ 1‘ mac H I\ mm' m wH: I on ch lI IIIIIIIIIIIIIIIIIIIIIIIIII II" °‘ 440-KEV GATE WITH BKGD SBTD N . 2 l\ I\ mm 10- a m- _-I- o 0000 h h ‘H m o m I I —-98H.0 IIIIII III. < 500 1000 1500 2000 2500 CHANNEL NUMBER Fig. 24. (continued) JUZZ/uxTKU ENE WLIZDOO 123 447-KEV GATE WITH BKGD SBTD 455-KEV GATE WITH BKGD SBTD 467-KEV GATE WITH BKGD SBTD . 4mzz1500 keV. The tolerance for the right side of the figure was i0.5 keV. A semicircle at the origin of a transition indicates some coincidence data support for such a placement. 153 E Wow AvQDCflucoov .mN .wwm mm VONQQ 0.0 0.0 Ndmw Ndmm QMNN. Wanl'nl II INIQNHII I Imqumll'n I I 9%: . 9c.- u 9 9_9_ I—IIH I” E-flun M“ I .9 9. . IIIII 6:9 IIIHIIIII . 9.. Ill-IIII—ll IIIIIIIIII 9. a. II—nl-II-I-II- ..9 N lllllflflflfllflfllfl 9. a "LI-“Quflunlllllrlllllll n. v. VN _. wmmm WEI Ila o. o» 9 I89NNI .9999... 9 9. .. QLGWMM _IIII _IIIII w. |\IINII_mN IsW-Q3WI9IIIII__IIIIIII|I .Qmm 99.999 999mg 9==—=I—==_l_ Haw 9.9999 -I_=I=.I.I=I. 9.99M99--_mflflmfl_mmlml\lwmn ...9. —I—=I==I_I=l_ - 9”...” ..II9n.EEIm|l\I\”.mw9_9..9_9 IIodImmmI/IL v LflmInnnllln-Innnnlnnu- ZZInflnfllluIllllll$ IwIwIQM-nI/I 8HI 9 .999 9 9-99-.-_-= EEI flul Iwfik-EEI I 99999 9. .- 9=_ ___I_ _I__ _.-.__ 99-9 .....II: IE6 W99LIII I III III gmfialllflflnflfl' +9.. v" u .Wmumvvmflwnt IIIIIIIIII 9936.?ng I"""" .o «4 . 2,9299%" 9-=--- II I sumsz n“ N.N9w . we III-Inn 9099 III is . Hi 6m IIII IIII. Fina mouzulnn IIIII _ ommm 99.8.9 \ :mmmmw mwmmmlw ...... . 999999 990mm? ..9 be 89?992 @mVNv 918.0 E m.®® 3.1.5. Electror The I I pared with the ( and Fritsch et 9 about some of tI of data (my y 11 the pure E2 899 was 6.51x10'3 I these compariso and the predict the most unfort many 0f the reg data are just I were al50 us ed 154 3.1.5. Electron'Data and'Multipolarities The Y intensities from the present measurements were com— pared with the conversion-electron intensity data of Stockendal [St60] and Fritsch et al. [Fr58] in order to gain multipolarity information about some of the transitions seen in the Bi201+ e decay. The two sets of data (my 7 intensities, their electron data) were normalized for the pure E2 899.2—keV transition. The conversion coefficient used was 6.SIXI0-3 [$165] for an 899.2—keV E2 transition. The results of these comparisons (with theoretical conversion coefficients [S165]) and the predicted multipolarities are listed in Table 10. Perhaps the most unfortunate facet of this table is that it does not include many of the reasonably strong high energy y rays, but the electron data are just not available. The theoretical conversion coefficients were also used to construct smooth curves, upon which I have super- imposed the experimental points (Figure 26). Only a few error bars are included,since precise error limits were not available for most of the electron data. A few of the transitions have already had multipolarities assigned; these are discussed below. Internal converSion and scintillation measurements by Stockendal et al.[St58] indicate an experimental K-conversion co- efficient of 0.37:0.10 for the 289.2—keV transition. Since the theoretical value is 0.38 [Sl65],an assignment of M1 seems entirely reasonable, most of the error being due undoubtedly to the interfer— ence of the weak 291.3-keV peak. The Keelectron of the 670.7—keV transition was sufficiently Weak that only a lower limit could be obtained for the internal ”has nC\¢V-h l IC\.~ v 49:! I :- . odou- Hooo: ooon Ndmm NM I Anlvdn90 I I ”manlvfim96.‘ Amlvdm- wm .I- nm N.” N! S IIIIIIIIIIII N>WU~V hUthHOQ Many hUHIflQUn-N kn WQGUUIN RUMWIIU H‘UIIQII-HMUWI“ V K.HI¥ MOHUUUNUIMN CONWNWCIMH MN! HIUNUOHOOIFH IHUfl’: u 0N1” ‘90 IUWI‘i-QAIWUWII: 9°! IHDIPF IIIIIIIIIII lac! U 9":‘NU 9r -IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIuIIIIIIIIIa———————-—inuIImmm-IIIIuIIIIIIIIIIIIIIIIIIIIIIIIIIIIII -I. H2 2NI99.N HNIVo.H nNIvm.m ANIVn.H HHNIV9.n_ HNIom.n 99.H HoNHH onH H.9oH H2 HNIVa.N HNIVN.H HHIvo.H AuIvH.9 HHNIV9.9_ HNIVo.m 9.oH HoHo_ 9N» a.oao H2 HN-Vm.N ANIVN.H HHIvH.H HNIv9.9 HHNIve.oH aNIv9.o Nw.o How“ on 9.moo H2 HNIVa.~ “NIV«.H aHuvH.H aNIVn.9 HHNIvN.nH ANIv9.n oo.N HoHN_ oNN n.Hwo H2 RNIvn.9 . I HHIvo.N “NIvN.h HaNIvH.9H aHIVo.H 9N.o Hos. n9 9.man H2.N2 HNIVo.9 I HHIVH.N fiNIvo.n HHHIVM.HH aHIVn.H on.H HooN_ moN N.Nmn H2 Hvao.e I HHIvN.N ANIvo.w HHHIVn.HH HHIvN.H No.o HoNHH oHH N.NNn H2 aN-vH.n I HHIVn.N ANIVm.w HHHIvH.H_ HHIvo.H mm.o _onH_ o9H m.Hon ~2.H2 I I aHIvH.m aHIvo.H I HHIVn.N nH.o - ma «.mHa H2 HuIvH.a I HHIVm.m HHIvN.H HaHIvo.HH HHIVn.H an.o HoMN_ omH n.9H9 H2 HNIvn.~ I HHIVu.9 HHIVa.H HHHIVo.N_ HHIva.H oo.H HonH OHH o.HN9 H2 HNIvN.c HNIvN.m HHI99.9 HHIV9.H _AHIVN.NH HHIVa.N 9N.o HoNHH oNH H.NH9 H2 ANIVn.w ANIvn.n HHIVm.a HHIVo.H HHHIvo.HH HH-vm.N 9N.o HoMH_ ooH m.noa H2 HHIV9.H AuIvN.m HHIvo.m HHIVo.N HHHIvN.n_ HH-Vw.N 9m.o HONH_ onH H.Hmn m2.H2 aHIvo.H ANIvH.N HoVn.H HHIVa.H HHH-vo.m_ HHIvo.H Na.o Henna oNN 9.H9N H2 HHIVo.H HN-VH.N Havm.H HH-va.m HHH-V9.ma HHIVm.m ma.N HO99HH cmoH N.owN H2 HHIVn.N HH-Vo.H HavH.H HHIv9.m HHHIVw.n_ HHIvn.o so.N HonHH omON 9.99N nu H2 HHIVm.N HHIvH.H AoVn.N RHIvm.o HaHIVo.oH aHIvN.m 9N.o Hole cos 9.09N 1i mm.N2 HHIVm.n “HIvN.H Hovo.n HHIvo.~ HHHIv9.N_ HHIv9.N NN.o How. on m.NNN H2 HHIV9.n HH-vH.H HovH.m HH-vH.m HHHIvH.oH HHIVm.e oo.H Hoaal osoH N.NNN NM aHIvn.n HHIVa.H Hovm.n HHIvN.w HHHIVn.HH AHIva.H 9H.N _ooml non n.9HN H2 RHIVN.n I Hovn.n HHIVo.o HHHIVo.wH HHIVm.w Nm.H HomoH_ omaH H.0HN N2.H2 I aHIVn.H Havo.9 HH-VN.o HHHva.H_ aH-vo.n 9H.o _om_ con 9.NHN H2 I I Havo.H HoVn.H HHovH.HH Havm.H .o.H HONmH. ooNN N.oaH H2 I I Hoes.» HOVH.H HHHIVa.a_ HavH.H o~.° monH oaa no.99H m2.H2 ona.a I Hovq.H Hon.N HHHIvo.oH I am.c HONNHH I om.o9H um I anIan.o I I 9HAmIan.o. HnIan.om o.oon HoooHH ooon N.99¢ mu «2 N2 H2 IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII. IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII- H>9sv huHHIHom Mu bananas.“ Mann—35 .3360 I.“ 9.3: “fie Hauuuouoonh Huang—95mg 0 soul» no.3 0301». do.“ w.“ manna. I!!! aaoHanauuu r 99NHn no h3332.332 .oH oHauu ar¢I\V r. If \C C H! Aulv¢.H I pulse 4 roI3o F nh9H! afllvm9H AnlvN.m ava€.o AvawIN mavan.H~ «NIvaH H! HNIvN.N Amlvo.m Aulvm.o Aulvn.n HaNIv¢.na Aulvo.n a! Awlvn.N H~Ivo.H HNIvo.m “NIvo.n Hamlvm.nH amlvw.u nh9H! Aulvv.N ANIVO-H AuIvo.m anlvw.n I aNIvo.n mfi.h hm90 009° NQIH Home 9: meme nv Home em I no NVUIINUHOUV N.Hmn N.me v.®Hk n.0um ION ”Nan-N 156 .mmHuHumHOAHuHaa vuumwa oau now m¢=Hm> no Hmowuwuounu was .uw . H meuHuwHOQHuana wounwu Uta now wosan> n5 Hmowuuuoasu was .Hur Houaoaauwnxu .mwwuwmsmuaw nouuuamol nouuuouo onu we saw wan on on anon: av anon >wxl uouuomao Bonn muoxouun awsuwa muHuHmaouaH douuuoHoIM w>HuIHun Anuvo.w Awuv<.H Awlve.d Aulvo.H ANIvN.~ nunvn.~ Auuve.u AmIvm.m Amuva.o HnIvN.w HMIVs.9 ANIVo.H HNIVa.H .wuwv haul» was nouuuoflo onu oNHHmshoa on cow: was Encamu mm as HHHIvN.H 999-VH.9 Hm nAoVo.q anovh m NE nNIv~.~ Awlvo.w Aulvo.e Amlve.o “alga.” HuIvm.w Aulvc.o 99999.N 999-99.N HE :Afilvm.c nonm N H! Aalvn.w AuIvm.H ANIvo.H a~nvo.~ anlvm.n Aunvo.n “unvo.m nmwmumH monouowou Eouu mumxowun uaonuHa mowuHmaounH no Hon¢.m saqnvm.m SAHlv09N 9HoVn.H. 99999.H Amlva.w HHnIvo.oH Hm-va.H HANIVw.H_ ANIVw.~ HHNIvn.HH ANIVm.H mawlv¢.mH Awlvo.n Ha~lvw.na Awnvw.o Amlvo.n HuuaoaHuwmud .moHuncouaH nouuooHoIQ 0>Hunauu u: ow In: sown >ox|c.NHa on» u .Hnodwa :« aw>ww mucwuuwwwooo Hafiwuo>uoo scum umuwmwua manauw Scum M .mowuwmaouaH :ouuuma0um meumH Scum wouwasoawo muoxomup u: .haobwuuommwu assumes awash H .hHo>Huuoamwu HQ 0>HuIHou uaouounou muons: .Amuoaunaauu >oxlo.uno was vuasmoum mum sounuv meuma was meumu moonwuomwu aH no>Hw moHuHmam n.HHm onu mo auamaound nouuooHo wau wdHuumuunam he was I~.HHm may we mafiuwmflwuflw unH nouuumHo osu scum Amm ow buwmnouaH couuowHw scam u voumaoauouaa Honuouoozy w you ondmb Hauuuuuoonu uzhw 9 wflfiuwmfiflufifl ocuHa mosHm>v .xuol uawmmua aouu moHUHmaouaH haul» u>Humex o mw.o ca.o mo.~ n.0H q.AH mm.m ma.o om.o ~¢.H .mwmuhu «economwu uuuoHoIM o>HumHoM A .mvaum uaommum scum wmumuwcma I Hooou I gem amenmgsooq I 9N HoHHH nNH mmoonamen Hose oOH Hon_ 99 Home o9 I no Auoauwunoov III-I--II-Iquuuuuuuuuuuuuunnunnfl ¢.ow o.qwm m.qu ~.ooa w.mo~H n.mHo o.NHm «.mmn N.nmn ¢.an n.0Hn .OH mHnnH 157 M2 0 ELECTRON DATA FROM (3160) ' ELECTRON DATA FROM (Fr 58) o 0 SAME AS 0 I00 200 300 400 500 600 700 800 900 IOOO ENERGY (keV) Fig. 26. Experimental conversion coefficients for some szoL+ transitions. The smooth curves of the theoretical ax were prepared from tables in [$165]. j} i I I I Kconversion cc the E1 and E2 n For polarity assigI $68]. The in several exc- ES characters, Neither of the pole. Krohn a ments on B120“ and that the 9 a1» I99- 99- howeVer, they Perhaps, this 158 K conversion coefficient. However, this limit definitely excludes the El and E2 multipolarities [St58]. For the 899.2—keV transition, the most probable multi- polarity assignment is E2, as established by [St60,Kr55,He56, and St58]. The 374.7- and 911.7—keV transitions have also been studied in several excellent investigations and their predominantly E2 and E5 characters, respectively, are well established [St58,St60,Kr55,He56]. Neither of these transitions,though,was predicted to be a pure multi— pole. Krohn and Raboy [KrSS] found from angular correlation measure- ments on Bizo‘+ that the 374.7-keV y is E2 with a 0.5% admixture of M3 and that the 911.7—keV y is E5 with a 1% admixture or M6. Herrlander et a1. [He56] found a maximum admixture of 0.5% M6 for the 911.7-keV y ray, however, they attempted to separate the Pb2°”m from B120!+ in their work. Perhaps, this explains why they found a lower admixture limit. With the advent of the realization that the 911.7—keV peak was only part of a closely-spaced doublet, I think I now can explain the hitherto "impurity" in the E5 transition. The previous measure— ments were taken not on the 911.7-keV peak but on the 9ll.73+911.96— keV doublet. The multipolarity of this additional 911.96—keV V was calculated from my y intensities and Stockendal's [St58] electron data by assuming the 911.7—keV y ray to be a pure E5 transition, and using the theoretical conversion coefficient to remove the K electron intensity due to the 911.73-keV transition. When this is done and the K conversion coefficient calculated, it is very clear that the 911.96— keV Y is an M1 transition. What the previous experiments have seen then is not an admixture of E5 and M6 but an admixture of E5 (from the 911.71 theoretical con calculated that qualified assum accurately sepa that 326% is re Curl Spin and paritj moment for a f- the experiment Experimental) mated decay en Percent feedin which do not h was an M1 mult as moSt 0f the Using the modj to each State 159 (from the 911.7—keV y) and M1 (from the 911.96—keV y). Using the theoretical conversion coefficient for an M1, 911.96—keV y,I have calculated that 1% M6 is equivalent to 326% M1. Considering the un— qualified assumptions on the multipolarities and the difficulties of accurately separating the electron and y-ray intensities, I think that 326% is remarkably close to the 45% that one might have predicted. 3.1.6. Spin and Parity Assignments for PbZO” Curbing the lemming urge to dash headlong into the actual spin and parity assignment discussion, I want to side—step for a moment for a few (hopefully) words of scientific enlightenment. Using the experimental photon intensities for Bizou, the calculated (or experimental) multipolarities of a few of the 3120” y rays, the esti— mated decay energy, and the t%,one can calculate the log ft's and percent feedings to each of the states in szou. For those y rays which do not have calculated multipolarities, I assumed that each was an M1 multipole (for the purpose of calculating the log ft's only) as most of the calculated y rays were Ml's anyway (see section 3.1.5.). Using the modified DECAY SCHEME program, the feedings and log ft's to each state were calculated; these are found in the left-hand col— umn of Table 11. However, a consideration of the peculiarities of the BiZOLI decay leads me to question the validity of such a list. For example, consider the 899.2—keV excited state. This state has both an abnormally high Z feeding and subsequently low log fi. Because the 899.2—keV state is 2+, this would involve a fourth- forbidden transition from the 6+ Bizo1+ ground state. Consequently, one would expect a considerably larger 10g f? than the 8-1 actually Table l Excited state (keV) 899.2 1273.9 1562.8 1817.3 2065.1 2185.4 2257.9 160 Table 11, Percent feedings and log ft's for the excited states in szou. Excited state Percenta Log fta Percentb Log ftb (keV) feeding feeding 899.2 10.14 8.06 0.0 large 1273.9 0.0 large 0.0 large 1562.8 1.16 8.80 1.46 8.72 1817.3 0.0 large 0.0 large 2065.1 1.86 8.44 2.34 8.34 2185.4 10.43 7.64 0.0 large 2257.9 26.75 7.15 33.68 7.10 2385.8 0.61 8.79 0.77 8.69 2434.0 0.28 9.11 0.35 9.01 2480.0 1.00 8.53 1.26 8.43 2506.8 0.0 large 0.0 large 2919.5 2.69 7.86 3.38 7.76 2928.5 9.74 7.30 12.26 7.20 3029.0 2.82 7.77 3.55 7.67 3092.0 3.56 7.62 4.49 7.52 3104.9 0.0 large 0.0 large 3170.0 15.03 6.93 20.06 6.82 3215.0 1.20 6.93 1.51 7.90 3232.0 2.06 7.75 2.60 7.65 3637.8 5.51 7.75 6.94 6.82 3768.4 2.03 7.09 2.56 7.06 3782.0 1.07 7.22 1.34 7.32 3814.4 0.22 7.42 0.28 7.95 3826.2 0.27 7.95 0.33 7.85 3842.2 0.03 8.83 0.04 8.73 3875.7 0.06 8.50 0.08 8.40 3996.1 0.03 8.59 0.03 8.49 Table 11. (c‘ 4080.5 4165.5 4249.6 a: aCalculated v from transit b Corrected va and 2185 .4-k 161 Table 11. (continued) 4080.5 0.18 7.47 0.23 7.37 4165.5 0.09 7.35 0.12 7.25 4249.6 0.06 6.03 0.33 6.03 aCalculated values from the relative beta intensities as determined from transitions pepulating and depopulating each state. Corrected values after the relative beta intensities to the 899.2— and 2185.4—keV states were arbitrarily set to zero. found. Two poss first, many weal from higher-13111 and second, the 2+) in B120“ wh 111sz“? Such account for son 899.2-keV leVeI Presently in tl fluctuations ( after bombardm atgmnent is fe Cerning the p] calibration e1 162 found. Two possible reasons for the discrepancy are available: first, many weak Y rays may be feeding the 899.2—keV state directly from higher—lying states (but unobservable in the coincidence data), and second, there may be a low—lying low-spin isomeric state (e.g., 2+) in 31204 which directly populates the 2+ 899.2—keV excited state in PbZO”? Such a feeding (from a 2+ B120l+ isomeric state) would account for some of the unexpectly large percent feeding to the 899.2—keV level. A preliminary test for such a possibility is presently in the planning stages. By observing the intensity fluctuations (if any) in the 899.2—keV peak as a function of time after bombardment, one should get some idea of whethér such an argument is feasible or not. Another argument might be made con- cerning the precision of the intensity calibrations. Since the calibration error ranges from 5 to 15% for peaks of reasonable size (i.e., >3Z of the 899.2—keV peak), much of the 10.1% feeding to the 899.2—keV state could be due to calibration errors in the intensities of the y's populating and depopulating the 899.2-keV state. It also appears that only the high—spin states are populated by the a decay of the 6+ B120” ground state. It is almost a certainty that there are other low-spin states which are only weakly populated and are, therefore, difficult to place using the present techniques (because the transitions are weak). Presumably, these states would feed other low-spin states, e.g., the 2+ 899.2-keV state. This, in turn, would decrease the large percent feeding and increase the subsequently low log ft. One or more of the forementioned pos- sibilities makes it understandable why such a large percent feeding was found for 1 Als< have to be a ti state to the 9- log ft. The 5] previously est; 0f such an ass As I have been the 2185.4—kev 3 transition ( “early an the higher-lying h decrealso. the f 163 was found for the 2+ 899.2—keV state. Also, consider the 2185.4—keV isomeric level. It would have to be a third—forbidden 8 transition from the 6+ Bizou ground state to the 9— Pb207m isomeric state and as such should have a large log ft. The spin and parity of the 2185.4—keV level has been previously established as 9— [Fr58,St58,Kr55]. It is on the basis of such an assignment that the following argument can be made. As I have been unable to identify any of the y's directly feeding the 2185.4—keV state, the log ft "appears" to be 7.6. However, this thransition (to the 9— isomeric state) is third-forbidden and nearly all the populating intensity should come from Y feeding from higher—lying high—spin states. These would have the tendency to decrease the feeding and increase the log ft. A much more accurate set of percent feedings and log ft's might result if arbitrarily I were to set the input and output tran— sition intensities equal for these two states, i.e., assume no 8 feeding to either of these states. The right column of Table 11 shows the result of doing this. One could argue that what I have done is to arbitrarily force the data into values I want to believe. Rather, this set of feedings and log fi's represent what should be more realistic values for these parameters in light of all the present and Vpreviously reported data. Note that the log fb's are increased by only about 0.1. 3.1.6.A. Ground, 899.2—, 1273.9—, and 2185.4—keV States The ground state is assigned 0+, as would be expected for an even—even nucleus ( szo“). The remaining three levels comprise 82 122 a Portion of the Pb20”m decay scheme and as such have been thoroughly hwestigated ( 911.7-keV E5 t EZtransition. sequence for t by the details ‘ [Kr54,Kr55],aI ‘ pole mixing t¢ Holland et al imation (DWBA quence. Thus keV states sp these assignn data. 164 investigated (section 1.2.5.). These investigations revealed a 911.7—keV E5 transition, an 899.2-keV E2 transition, and a 375.0—keV E2 transition. These suggest a 0+, 2+, 4+, 9— spin (and parity) sequence for the states in PbZOHm. This sequence was also confirmed by the detailed angular correlation experiments of Krohn and Raboy [Kr54,Kr55],although it was necessary to assume some small multi— pole mixing to account precisely for the results. The (p,t) data of Holland et al. [H069] and the associated Distorted Wave-Born Approx- imation (DWBA) calculations also suggest the 0+, 2+, 4+, 9— spin se— quence. Thus, I also assign the ground, 899.2—, 1273.9-, and 2185.4— keV states spin and parities of 0+, 2+, 4+, and 9—, respectively, as~ these assignments are also internally consistent with the present data. 3.1.6.B. 1562.8—keV State The 1562.8-keV state was first revealed by Fritsch et al. (section 1.2.5.A.) in their study of the Pb2°“m decay. They found a 622.2—keV E5 Y depopulating the 2185.4-keV isomeric state and a 289.2—keV M1 Y depopulating the 1562.8—keV state. This latter multi— polarity was also confirmed by the present data (Table 10). The M1 character of the 289.2—keV transition suggests a 3+, 4+, or 5+ assign— ment. The 622.2-keV E5 Y depopulating the well—known 9- isomeric level suggests 4+ or 14+. The rather large log ft (for the B120“ decay) of 8.7 would appear to indicate an allowed or first-forbidden tran— sition. However, not all the y's feeding the 1562.8—keV state have been placed with a high—degree of confidence. This means that the 10g ft most likely should be larger than 8.7. Because of this, I suggest that i transition fry value is inco assignment fo 3.1 Th 1 immediately 1 log ft, being calculations 3+ cannot be and triton. . 165 suggest that the possibility that it is really a second-forbidden transition from the 6+ B120”,is not ruled out. While the log ft value is inconclusive the remaining data appear to suggest a 4+ assignment for the 1562.8—keV state. 3.1.6.C. 1817.3-keV State The very strong 918.3—keV E2 Y to the 899.2—keV 2+ level immediately limits the possible assignment to 0+ through 4+. The log ft, being arbitrarily large, tells one absolutely nothing. DWBA calculations by Holland et al.[Ho69] suggest a 4+ assignment, although 3+ cannot be excluded because of the intrinsic spins of the proton and triton. Some minor information can be obtained from the non— existence of specific transitions (if one is careful). One might assume that the spin is 55 as szoum does not appear to populate this state. Also, nothing (i.e., no transition) appears to p0pulate both the 899.2— keV 2+ state and this level, which might lead one to say that the spin is 24. This last argument is weak, but it does add a small measure of evidence to a 4+ assignment, although 3+ cannot be ruled out entirely. 3.1.6.B. 2065.1-keV State The 791.2—keV Ml Y transition (to the 4+ 1273.9-keV state) suggests a possible assignment of 3+, 4+, or 5+; similarly, the 501.8— keV M1 y transition (to the 4+ 1562.8—keV state) also suggests 3+, 4+, or 5+ assignments. The log ft of 8.3 probably implies an allowed transition (negative parity states ruled out on basis of the M1 tran- sitions) which would allow spins (and parity) of 5+, 6+, and 7+. Combining the log ft and multipolarity data limits the assignment to 4+ or 5+. Little more can be deduced from the higher-lying levels, so the state at 2065.1 keV is assigned 4+ or 5+. The intensity balance on this i I t f I level appears limits the as: 3:; Th of the 984.0- vhich is almo or 7+ assignm this point, sc unfortunate 5 Upon this lei assignment. 166 level appears to be quite good and can probably be trusted. This limits the assignment of the 2065.1—keV state to 5+. 3.1.6.B. 2257.9-keV State The state at 2257.9 keV is assigned 5+ or 6+ on the basis of the 984.0—keV E2 Y (which allows 2+ to 6+) and the log ft of 7.1 which is almost certainly an allowed transition (suggesting a 5+, 6+, or 7+ assignment). No preference between 5+ and 6+ is available at this point,so they are assigned with equal weight. Actually,this is unfortunate since many of the high—lying states will have to be based ,upon this level, but (tragically) the data do not warrant any other assignment. 3.1.6.F. 2385.8—keV State The only concrete evidence for the assignment of this level is the log fb value, inasmuch as the multipolarities for both depopu- lating y‘s are unknown. The high log ft of 8.7 suggests an allowed or first-forbidden transition ,i.e., an assignment of 5:, 6:, or 71. Assuming the y's to be M1, E2, or El,I find possible assignments of 2+ through 7+ and 3- through 7-. From the log ft alone, then, I suggest an assignment for the 2385.8—keV state of 5:, 61, and 71. 3.1.6060 2434.0-keV State The 176.2-keV M1 transition from this state (to the 5+ or 6+ 2257.9-keV level) implies an assignment of 4+, 5+, 6+, or 7+. The log ft of 9.0 is one of the largest of any of the szou levels. This probably suggests an allowed transition (first-forbidden ruled out by the.Ml). This suggests 5+, 6+, and 7+ assignments. Eliminating the non- common elements, I propose that the 2434.0-keV state is 5+, 6+, or 7+. 5+, 6+, or 7+ i a first—forbi ‘ sition can be 1 as positive. keV state. 3.1 Ti the state m . of - parity 1 is terribly reduced furt‘ must be p0pu known 241's), 167 3.1.6.B. 2480.0—keV State The 222.2-keV M1 y to the 2257.9—keV state allows a 4+, 5+, 6+, or 7+ assignment. The log ft of 8.4 would appear to suggest a first—forbidden or an allowed transition. The first—forbidden tran— sition can be ruled out since the M1 transition extablishes the parity as positive. This leaves, therefore, 5+, 6+, or 7+ for the 2480.0— keV state. 3.1.6.1. 2506.8—keV State The 248.9—keV M1 y to the 2257.9—keV (5+,6+) state limits the state to 4+, 5+, 6+, or 7+ and also eliminates the possibility of - parity states. The log ft tells nothing about this state. It is terribly frustrating that the assignment for this level cannot be reduced further,as there are 5 higher-lying states (some of which must be populated by allowed transitions) which feed this state (3 by known Ml'sL implying a 4+ to 8+ assignment. The data appear to jus- tify only a 4+, 5+, 6+, or 7+ assignment for the 2506.8-keV state. 3.1.6.J. 2919.5-keV State The level at 2919.5—keV is assigned 5+ or 6+. 0n the basis of the low log ft of 7.8 one would expect an allowed or first-forbidden transition. The possibility of negative parity states is eliminated by a 661.6—keV Ml Y to the 5+ or 6+ 2257.9-keV state (allowing a 4+, 5+, 6+, or 7+ assignment) and by a 412.2-keV Ml y to the poorly known (4+ to 7+) 2506.8—keV state. Note also, that a 1645.6—keV y populates the 4+ 1273.9-keV state, but none is found to populate the 2+ 899.2—keV state. This weakly suggests a 25+ assignment, which is consistent wit the A+(3+) 18] rule out 7+ as E Th4 soning as for same states. external quan M1 Y to the 2 The 4+ assign ft of 7.2, 3, result, the 2 being Veakly keV State (C1 I68 consistent with the present assignment. The 1102.2—keV y populates the 4+(3+) 1817.3-keV state; on this basis one might tentatively rule out 7+ as a possible assignment. 3.1.6.R. 2928.5-keV'State The assignment for this state follows exactly the same rea- soning as for the previous state, having analogous transitions to the same states. A 421.6—keV Ml y to the 2506.8-keV state would suggest external quantum numbers of 3+ to 8+. However, a strong 670.7-keV Ml y to the 2257.9-keV level rules out the 3+ and 8+ possibilities. The 4+ assignment can be discarded on the basis of a quite low log ft of 7.2, an allowed normal or Z-forbidden transition. As a result, the 2928.5—keV state is finally narrowed to 5+ or 6+, the 7+ being weakly ruled out by the strong llll.3—keV y to the 4+ (3+) 1817.3- keV state (cf,analogous transition in section 3.1.6.J.). 3.1.6.L. 3029.0-keV State The 522.2—keV Ml y transition to the 2506.8—keV state would suggest that the 3029.0—keV state is 3+ to 8+, not very selective,to be sure. This can be limited to 4+ to 8+ as a result of the weak 100.7-keV Ml y to the 2928.5—keV level. The log ft of 7.7 is some— what high for an allowed transition, but considering the undoubtedly complex structure of 4—neutron-hole states (possibly core-coupled), one would expect the 8 transition to be hindered. Assuming, then, an allowed transition rules out 4+ and 8+, this leaves the 3029.0-keV state with possible assignments of 5+, 6+, or 7+. The 1755.3- and 1211.7—keV y's to the 4+ 1273.9- and 4+ (3+) 1817.3—keV states, reapec- tively, also shakily rule out the 7+ assignment. This means the state at 3029.0 keV Ll. Sol assignment of tunately, no to the 1817.3 M2, or E2, on consequence I St or 6:. Th goes to the 4 3.] ‘ T1 0f the trans: States and a] Can be filled Will be show a; ,._. ’6‘ S ('D a; H H n: "l 169 at 3029.0 keV has an assignment of 5+ or 6+. 3.1.6.M. 3092.0-keV State Solely on the basis of the log ft of 7.5,I propose an assignment of 5*, 6*, or 7=t for the 3092.0—keV level. Rather unfor— tunately, no electron data are available for the strong 1274.8-keV y to the 1817.3—keV state. Assuming that the 1274.8-keV Y is an M1, E1, M2, or E2, one might be tempted to rule out 7: as a possibility. As a consequence I somewhat riskily, suggest that the 3092.0—keV state is 5: or 6i. This assignment is weakly supported by a 1958.1-keV y which goes to the 4+ 1273.9-keV state. 3.1.6.N. 3104.9—keV State The state at 3104.9 keV is assigned 4+ to 8+ on the basis of the transitions to the 5+ or 6+ 2257.9- and 4+ to 7+ 2506.8-keV states and an arbitrarily large log ft. The negative parity states can be ruled out by an M1 532.7—keV y from the 3637.8-keV state which will be shown shortly to be 5+, 6+, or 7+. 3.1.6.0. 3170.0-keV State The log ft of 6.8 for this level is the second lowest in the present BiZOL+ decay scheme and this obviously would suggest an allowed transition (or possibly a first—forbidden but this will be ruled out by an M1 from positive parity states, as discussed below). This implies an assignment of 5+, 6+, or 7+ Confirmation of this comes from a 912.0-keV M1 Y to the well-known 2257.9-keV state (5+ or 6+). I can thus suggest a 4+ to 7+ assignment. Also, a 140.8—keV M1 y to the 3029.0-keV level suggests the range of 4+ to 7+. Coupling these possibilities rules out the 4+ and reduces the 3170.0-keV state to either 5+, 6+, or 7‘ state would ment is now 3' I. log ft is kn an allowed c and a 718,4 SUggESt Spj 170 5+, 6+, or 7+. The existence of a transition to the 4+ 1273.9—keV state would appear to remove the 7+ possibility, so the final assign— ment is now 5+ or 6+. 3.1.6.F. 3215.0-keV State Little can be said about this state,inasmuch as only the log ft is known. The 7.9 log ft value would appear to Suggest either an allowed or first-forbidden transition, thereby implying 5i, 6:, or 7:. It is tempting to call the 1652.0—keV an M1 or E2 transition but I can find no overt rationale for doing so. But, as it populates a 4+ state, I am only somewhat poorly justified in ruling out the 7i. This reduces the assignment to 5: or or for the 3215.0—keV state. 3.1.6.Q. 3232.0-keV State The log ft of 7.6 for this state seems somewhat high, but, once again, allowing for the complex internal structure surely to be associated with some of the PbZO'+ levels, this seems to suggest an allowed transition and a 5+, 6+, or 7+ assignment. The — parity states (from a first-forbidden transition) were ruled out because of a 725.2—keV Ml transition to the 2506.8—keV state, though this does not limit the Spin assignment at all. The strong 1414.7—keV y to the 4+ (3+) 1817.3—keV state might mean that one could be pardoned the sin of ruling out 7+. The same can be said of the 1958.1-keV y. I postulate a 5+ or 6+ 3232.0—keV state. 3.1.6.R. 3637.8—keV State TWO Ml's, a 709.1—keV y to the 5+ or 6+ 2919.5—keV state, and a 718.4—keV y to the 5+ or 6+ 2928.5—keV state both appear to suggest spin and parities of 4+ to 7+ for the 3637.8—keV state. The very low (fo: transition at is subsequen keV state ce i T 7’: on the ba 01‘ first-for the 2065.1—k very low (for szou) log ft of 6.8 surely implies an allowed 8 transition and a 5+, 6+, or 7+ assignment. The level at 2627.8 keV is subsequently assigned 5+, 6+, or 7+. The 1203.8-keV y to the 2434.0— keV state certainly does not conflict with such an assignment. 3.1.6.5. 3768.4—keV State The state at 3768.4 keV can only be assigned 5i, 6:, or 7i on the basis of its quite low log ft 0f 7.1 (suggesting an allowed or first—forbidden 8 transition). The very strong 1703.3-keV y to the 2065.1—keV level very likely is an M1 or E2 although no electron data are available (tragically); this precludes any further legitimate reduction in the assignment. However, as it appears more likely that allowed transitions are hindered than first—forbidden transitions accelerated, I postulate only the + parity states, or 5+, 6+, or 7+. 3.1.6.T. 3782.0-keV State The log ft of 7.3 indicates an allowed or first—forbidden transition. This suggests 5i, 6i, or 7i. The three depopulating transitions to the 5r, 6f, or 7i 2434.0—keV state, the 4+(3+) 1817.3— keV state, and the 5+ or 6+ 2257.9-keV state would appear to suggest that the 7: assignment can be tentatively ruled out.v On this basis I Pr0pose that the spin and parity assignment for the 3782.0—keV state is Si or 6:. 3.1.6.U. 3814.4—, 3826.2—, 3842.2—, 3875.7—, 3996.1-, 4080.5—z 4165.5—, 4249.6—keV States Each of these has been assigned a spin entirely on the basis of the admittedly shakey log ft values. In inverse order, the transition to the state at 4249.6 keV is almost certainly an allowed transition, 91:20” log ft state. The keV, respect forbidden t! The next thi assigned 5:, 3.4, and 8.". 3814.4 keV, 0f 7.8 and 1 these as al Si, 6:, or frightfully f l 172 transition, its 6.0 log ft being the lowest (by 0.8) of any of the szou log ft's. This suggests 5+, 6+, or 7+ for the 4249.6—keV state. The log ft's of 7.2 and 7.4 for the states at 4165.5 and 4080.5 keV, respectively, appear to be be indicative of an allowed or first— forbidden transition, thereby implying 5:, 6i, or 7i for these states. The next three lower levels, at 3996.1, 3875.7, and 3842.2 keV, are also assigned 5i, 6i, or 7: on the basis of their higher log ft's (8.5, 8.4, and 8.7, respectively). The final two levels, at 3826.2 and 3814.4 keV, fall in an unfortunately ambiguous region, having log ft's of 7.8 and 8.0, respectively. I finally decided once again to classify these as allowed or first—forbidden 8 transitions, thus suggesting 5i, 6:, or 7i as possible spin (and parity) assignments. It is frightfully tempting to call these last two allowed transitions,as one would expect the log ft's to be large,owing to the almost certain complex particle—hole rearrangements which must occur in the B tran- sitions. Conservatism got the upper hand in these assignments,how— ever, and the negative parity states are thereby included. Each of these states (except for the 4165.5—keV state) has one depopulating transition to the 1562.8—keV state. This weakly suggests that the 7: assignment might be ruled out, but tells one nothing about the parity of the states. The 4165.5—keV state must remain as 5i, 6:, or 7i as its depopulating y is to the 5+, 6+, or 7+ 2434.0—keV state, which adds no information at all concerning the spin or parity of the 4165.5—keV state. 3.1.6.V. Comments This last section on spin and parity assignments necessarily concludes the theoretical c' level scheme however, I an the process < associated e: remain extret decay scheme harm to late: lead others I decay scheme scheme Which 173 concludes the B1201+ experimental sections. The theoretical or semi- theoretical discussion of the meaning (or "so what") of the PbZO” level scheme is left to a later chapter (Chapter IV). Before leaving, however, I must express a note of personal pessimism. Throughout the process of constructing the B1201+ decay scheme and making the associated external quantum number assignments,I have attempted to remain extremely pessimistic and conservative. In such a complicated decay scheme to do otherwise would possibly be to do irreparable harm to later investigations of the same isotope. Rather than mis— lead others by constructing an impressively large and complicated decay scheme of only ”half—baked” data,I have chosen to propose a scheme which is smaller but much more firmly founded. 3.2.1. Intn .11 thus enablin; 31203 source (by half-11f té's and, of the previous With a multi resulting wc Ported some Fritsch [Frf [St60] me... Sitions by in an exter used Peman Novakov et Spectromete The highest sition, “h. 174 3.2. Electron Capture Decay Scheme of 81203 3.2.1. Introduction 1201+ Just as it was imperative to produce clean B sources, thus enabling one to identify the many 3120“ y rays, so it is with the 81203 sources. 31203 has the added difficulty of being inseparable (by half-life or chemistry) from B120“, these having nearly identical t%'s and, of course, identical chemical properties. As a consequence the previous investigations of 31203 [Fr56,N058,St60] had to contend with a multitude of B120” peaks, many only poorly identified; the resulting work was anything but complete. Novakov et al. [N058] re- ported some 20 transitions from conversion-electron studies, and Fritsch [Fr56] reported essentially the same list, while Stockendal [St60] measured the internal conversion coefficients of several tran- sitions by comparing the conversion lines to the photolines excited in an external uranium converter. Both Novakov et al. and Fritsch used permanent—magnet spectrometers in their investigations, but Novakov et al. have also used double—focusing B and scintillation spectrometers, e—Y and y-y coincidence measurements in their work. The highest y—ray energy reported to date has been a 1896—keV tran— sition, while the decay energy has been reported to be 3.2 MeV [V166]. Thus, once again, a number of high—lying levels, as yet unplaced, might be expected. Novakov et al. have ventured to propose a tentative de- decay scheme based upon their e—y and y—Y coincidence work (Figure 27). While the decay scheme of Bi203 seems to be more concretely rooted by Novakov's coincidence data than B120“ was by the work of Fritsch et al. [Fr58] and Stockendal et a1. [St58], with recent Fig. 175 1846 l896 / _ 5/2-(g/g-)"—f_MI 2636 6ls ' (240) I3/2+ ' 8l9.7 ”2'9”" M4 MWEZ) mmm 825.2 BIS] M 1 846.7 (590) (2340) l0336 (2'00) (230) 60.3 _ Ml- l86.5 3/2 l/2- '263 I265 5/2— 52- 0 EC 27. Previously reported B1203 decay scheme [N058]. advances in is nw reaso the 131203 de truth, some than previou the previous discussed it i Separated is with 40—45 1 The details Were discus identified taking Spec and noting out. The 1 ing Samples analyzing t Were “Megs techniun. 176 advances in Ge(Li) Spectroscopy technology and the fact that 31207 is now reasonably well—known, it was felt that a re—investigation of the B1203 decay could yield a great deal of new information. In truth, some 147 y rays were identified, this being some 122 more than previously reported. Many changes and additions were made in the previously proposed decay scheme for B1203. These changes are discussed in the subsequent sections. 3.2.2. Source Preparation The B1203 sources were prepared by bombarding 97.22% Pb206 separated isotope (as Pb(NO3)2, obtained from ORNL Isotope Division) with 40—45 MeV protons from the MSU cyclotron for 1—2 h at 1-2 uA. The details of this production (including excitation function studies) were discussed in section 2.1. The short—lived contaminants were identified (most notably 131202, t%=1.6 h, and 913202“, t%=3.6 h) by taking spectra of the samples at various times after the bombardment and noting the large intensity variations of the peaks as they die out. The long-lived contaminants (B1205’206) were revealed by count— ing samples after they have been allowed to decay for 3—7 days and analyzing the remaining peaks. Once again no chemical separations were necessary, making this an easy radioactive source preparation technique. 3.2.3. B1203 x-Ray Spectra 3.2.3.A. Singles Spectra The same tw0 detectors described in section 3.1.3.A. were used to dete However, whe the Biw’ Sp used during 2.1 keV Mir '1 well-known t and efficiex calibrating ‘ Calibration 6- Just as i Was detemi I of these pe Curve, whic Curve then . from their 177 1203 used to determine the energies and intensities of the B Y rays. However, whereas the 2.5% Ge(Li) detector was used primarily for the 3120” spectra, the 3.6% Ge(Li) detector was the primary detector used during this study because of its better resolution (typically 2.1 keV FWHM at 1.33 MeV). The Y rays were determined by comparison with a number of well-known calibration sources listed previously in Table 5. A quick and efficient method of checking these energies was performed by also -203 calibrating the major peaks of Bi 20” ,using the Bi peaks as internal calibration standards. The B120” peaks so used are compiled in Table 6. Just as with the B120” decay, the centroid of each standard peak was determined by MOIRAE and/or SAMPO (section 2.3.1.B.); the centroids th of these peaks are fit to a least—square n (n = 2 commonly) degree curve, which then serves as the calibration curve. The calibration curve then returns the energies of the large unknown 31203 Y rays from their own centroids. The weak Bi203 Y rays were calculated by repeating the process, using the now well-determined large B1203 peaks as internal standards. A Y—ray singles spectrum of B1203 (and 3120“ concurrently) utilizing the 3.6% detector is shown in Figure 28. A list of the energies and relative intensities of the Y rays from the a decay of Bi203 is given in Table 12. The energies are the arithmetic mean values for several runs (2—3) taken at different times, different proton beam energies, and different Ge(Li) detectors. The corresponding uncertainties in the energies are slightly larger than the 3120% owing to fewer spectra that were averaged and be— cause of B120“ contamination, these uncertainties were: the major Fig- 2: 178 Team! trill}, +_.NN\.+w.wmh Id 3515555 .d, mama I i. . N i ...mom I L was“ 0.2m 1.. Bl203 SINGLES A. m O H (D m lb (NJ A“... Jr». .1- [\ . m l Jl -. ._,.. u. 1000 500 0.2:: + m.ooSIrI[1W 0.2.: It% mast liflMm was: ltflh w.mhoH 11AM m.:mmH I m mammalfia . 13.3an s ommHIJ mdomal . . Mai m.wm+; I. 0.31: + «225 I V. JL-L‘JVVAM19 382! «.mofil w 1.2:le W J m fimmo I [m 0.1mmmloooum It. 5. l4. 3 0 o 0 4m223% of the 820.2- keV Y ray) have statistical uncertainities ranging from r5—15%; the remaining peaks have intensity uncertainities up to 125%. The rel- ative photopeak efficiency curves (at various distances) for the 2.5% and 3.6% Ge(Li) detectors were calculated from measurements of stand- ard Y—ray intensity calibration sources. The results were, for con— venience primarily, incorporated into the MOIRAE E(I) program, allow— ing one to by-pass the relative peak area step completely. 3.2.3.B. Anti—coincidence Spectra What was previously said (section 3.1.3.E.) about the characteristics and validity of anti—coincidence data certainly still holds true. To summarize those comments: enhanced peaks in an "anti" may be non—cascade ground—state transitions or non—cascade transitions feeding a long—lived isomeric state, while little can be said about those peaks which are not enhanced. An anti-coincidence spectrum (Figure 18 shows a block diagram for the experimental set up) was collected on a B1203 source in attempt to reveal those direct non-cascade ground-state transitions or Y's feeding the 825.2—keV isomeric state. Figure 29 illustrates the Bi203 anti—coincidence spectrum taken using the 2.5% Ge(Li) detector, the SPlit NaI(T1) annulus,and an auxiliary 3"X3" NaI(T1) detector. The ? EDmFOmum uczuC_C2_CCI_b2< MON.0 184 .Hoqnou 05 mo paw nonuo on» us uouoouov AHHVHmz :mxzm M £53 mafia—Gm “5.3m QHvaz 05 mo Hon Inna man ovwmaw woooam soak uouomuow Afiqvoo Nm.N 93 .3 wovuooou Euuomm oodowwoaHOOIHuam mowwm ooom ss___. B'ESLZ — (gozll) +1192 — — mmmzsz I_ m zz50% of the events in the 126.3—keV peak are real (the remaining being chance events), which is sufficient to get an excellent "delayed"—coincidence spectrum from the prompt-coincidence data. For these reasons, plus time and expense consider- ations, no separate delayed—coincidence spectrum was taken. 3.2.4. Construction of the Pb203 Level Scheme Figure 31 shows schematically the s decay of Bi203 to levels in Pb203 as evaluated from my data. These 25 excited states and 51 Y rays were placed using primarily singles and coincidence data (taken under the EVENT RECORDER program), aided, of course, by intensity balances and energy sums. Much of what was said in section 3.1.4. about the logic and sequential construction of decay schemes holds equally true here and will not be repeated. Unlike 8120”, though, B1203 is a much more "typical" decay scheme. The ground state of Bi203 is 9/2—, while Pb203 has a 5/2— ground state, thus allowing for little possibility of direct feeding to the ground state as it would have to be a second—forbidden transition. The Bi203 scheme also has several transitions (not just one as in B120”) going to the ground state Pb203. The major advantage of the 31203 decay (over the BiZOL+ decay), though, lies in its much more intense transitions, even in the high energy regions. WWWR -N\.:.-N\m4.N\k .0 an .9 1N\I .-N\m ..NK .4 I. C. 0 .IL 3 0h .1 F . . .I |.|,l '4 192 (4.3%) 7.8 '2 IO ./ v~ N V. r. o (D (D e s! (O'HHI‘SZI (arrow-09 lg (Z'OZW'98I “29W“ _IW (O'OOI) Z'OZB III ‘9‘”) 3'9" I_ax-I “mm“ II—I' “"‘3’9'99" I—II ‘9'9”6'96°I I— l—_II (O'EZ)O'M78 (O'LZM' EEOI = I I II (9 OZ)9° 292 II “5‘3"” 33‘ —=%ii ‘92" 'l9'°-—I "WSW I_-. “5°?” 9“ =-—--I| (28' 2 9' Goal =I—I (66‘ Z)Z OOOI— «mm ..a. ‘96‘°’6'”9 --- ”W?“ --—-I . . -—-—--— W_--—-=_i-lll (£8 Z)€‘OZII . Il---—-I “"6 9°“ ---— ”Wm... lI-==_-I—! (L§I)O'|LJ.I (“mum II---_--—-- mm"-======--"- ””9"?” '-—-—--_l “93’9“?“ -_--—- (99'l)6‘9l8| -_-- -- “mm“ -—--—_23 + m I-m (BQ'O)E'€ HZ -- (90'17)9'826| I (29 Ht 699 II (98'2)8 8|]. —--III (6109-6, u IIIIl---—-l-ll (ggo) 1.999,". ---—--—- (won-g9; IIII II---_--—-- WiflfiEII-Il (ZO'Z)6'9vZI (stag-0°02 IIIIII I---=== (we) 7;”.3 llIII --- -—--III (622)9996‘ -IIIIIII_--==-—-Illl (09'§)9'IIOZ (19‘0) o-gzzz 'I-IIIIIII------—- l I“ 41“ MI 4'1““ N I... NN N A N A §§>>§I,>§.§§> s ¢ 2 * 7 _.-—"" ‘T‘d'i—Z: ‘ ch :-Q 3S31 + nu «n ... ’ — \ \ I I I cilQlQINN ({nglglfil 3C: 8 ‘Q’: 0‘ Bmcx'lQo'J NNN \\ \\ \\m \ - (D . - -\ \ \\ \ mmmm-cloa&asm m ({J _N (‘QAMQ‘OQU’ :o-ln ' +4 « ‘\«' "H ' " \ \ \ §&&& N&NN&Q & p Qm “ “k Nkkk Pk RR“ R " Fi . - g 31. The a decay scheme of B1203 proposed by the present study. All transitions were placed using coincidence data alone, W1thout the use of energy sums. 203 82 Pb A rather a lstic does in the all energies what less the decay transitic scheme. the "log: pIESEHte uPlaced' been we] (Sectiol ment wa whieh t Coincid Inasmu( is no ( a leve Pbgolm in the COQSU 193 A rather amusing, though not initially catastrophic, character— istic does present itself however. Because the B1203 Y rays in the singles are "obscured" by the 81204 "background" the energies and intensities of the Y rays of the 81203 are some- what less precise than they were for B120”, but, oddly enough, the decay scheme was easier to construct and the levels and transitions much more surely placed than those in the Bi20“ scheme. Without further verbage I would now like to tackle , the "logic" behind the construction of the B1203 decay scheme presented in Figure 31. 3.2.4.A. 825.2—keV Level The 825.2-keV 6.1-s isomeric state was not actually "placed" by the present investigation, but nevertheless has been well established by many previous investigations on Pb203m (section 1.2.6.5.). Additional evidence supporting this place— ment was found in the 31203 anti-coincidence spectrum, in which the 825.2—keV y is enhanced, and in the integral prompt— coincidence spectra, in which the 825.2«keV y is depressed. Inasmuch as this level has been well characterized (and there I is no overt reason for suspecting its placement), I also "place' a level at 825.2 keV, which corresponds to the 825.2—keV Pb203m state. 3.2.4.8. 126.4- and 186.4~keV Levels These states were previously placed by Novakov et al. in their tentative decay scheme [N058] (Figure 27) which was constructed from data obtained by conversion-electron spectro— metry anl work was spectros they do such a c their da the work spectra reveal 5 though 1 apparatl COincid intensi ities a 194 metry and e-y and y—y coincidence techniques. However, this work was performed before the advent of high-resolution Ge(Li) spectroscopy, and, while NaI(Tl) detectors are highly efficient, they do not provide the necessary high—resolution required for such a complicated decay scheme as that of B1203 . As good as their data were, one must be rather wary of blindly accepting the work as comprehensive. The 126— and 186—keV coincidence Spectra (found in Figure 33 at the end of section 3.2.4.) reveal strongly enhanced 633.8— and 847.0-keV Y's. (Even though the 126.4~keV state has a té of 75 ns, the coincidence apparatus had a lOO—ns resolving time, so not all of the coincidence data are killed completely.) The 633.8/847.0 intensity ratio in each spectrum is the same. Three possibil— ities are thereby suggested: 1) the 126.4— and 186.4-keV Y's are populating the same state, 2) the 126.4— and 186.4-keV y's are depopulating the same state, 3) the 126.4— and 186.4—keV transitions are adjoined by a 60—keV transition such that the 186.4-keV y Is the cross—over transition. When one considers that the 126.4—keV Y is an E2 (cf. section 3.2.5.) and the 186.4—keV y is an M1, it becomes evident that these transitions are among the most intense in the singles spectrum. Additionally, the delayed y—y coincidence data of Bergstrom et al. [Be6l] indicate that the L conversion electrons l with the L All these at 126.4 a coincidenc 847.0-keV I must ass these sta- study, an seems to then one intensiq 820,2—kel inteflsit I 820-2‘ke I another evidEnCe of Doebj S‘keV t] ‘ State_ in the p in turn 3, Cohsi 195 electrons of the 60—keV transition are in delayed coincidence with the L conversion—electrons of the 126.4—keV transition. All these data seem to lead me to confidently postulate states at 126.4 and 186.4 keV. In order to account precisely for the coincidence data (i.e., the very strong enhancement of the 847.0-keV y in both the 126— and 186-keV coincidence spectra), I must assume that there is indeed a 60-keV transition connecting these states. A 59.97—keV Y was definitely found in the present study, and, coupled with Bergstrom's coincidence data, there seems to be little doubt about these placements. 3.2.4.C. 820.2—keV Level The 820.2—keV y is the most intense y in the Bi203 y—ray spectrum. If this were not a ground—state transition, then one would expect to see other transitions of comparable intensity that would de-excite the level fed by the strong 820.2-keV transition. There are two y rays having relative intensities >SOZ, but neither of these is revealed in the 820.2—keV coincidence spectrum. As a result, 1 am led to place another level at 820.2 keV in the Pb203 level scheme. Further evidence for such a placement comes from the szoam studies of Doebler et a1. [D068] in which they showed that an unobserved S-keV transition competes with the 825.2—keV y from the isomeric state. (They really showed that an 820.2—keV Y was present in the Pb203m decay in addition to the 825.2—keV y, but this, in turn, implies the presence of the unobserved 5—keV transition.) A consideration of the intensities of the 825.2- and 820.2—keV 7's in th1 keV (rathl assignmen cursory s transitio detector detector cooled FE to 100 kg Singles [1 196 y's in the 81203 singles immediately suggests a state at 820.2- keV (rather than at 5 keV). With such a wealth of data, the assignment of a state at 820.2 keV seems quite unimpeachable. During the present investigation I attempted a cursory search aimed at confirming this unobserved S—keV transition. This search was undertaken with a Si(Li) x—ray detector having a 150 2 gold surface barrier contact. The detector is coupled to an ORTEC model 117 preamplifier with cooled FET first stage. The useful efficiency range is :5 to 100 keV. One Spectrum obtained with this detector in a singles mode is seen in Figure 32. Two problems worked against me finding the S-keV transition. First, the detector has somewhat poor efficiency for y rays in the 5-10—keV range. Second, as an m2 the S—keV transition will be highly converted and consequently be extremely difficult to detect with the Si(Li) detector. In Spite of all this,it appears that I may be observing the 5—keV transition in the x—ray Spectrum. A word of caution! The S—keV "bump" in Figure 32 is significantly broader than the other x—rays in the same region; consequently, this should not be taken as "proof” of the S—keV transition. In addition, because care was not exercised in preparing the x-ray sample, absorption by the sample and sample holder probably eliminated the relatively abundant conversion electrons. The experiment is presently being re—investigated. r U><0l> .10 x In. FLIP/KL: (. s 2 AMON.( ..lII |IIIJ II 197 .popsfloaw ma wheels 5 om mo umwa Huguuom a .uouoouop hmulx Asqvflm m nufia uoxou .mouwm mo sauuuonm hummus 36A .Nm .wwm mmmzoz gmzzoclx a no Am>80% of the photon intensity. These 51 Y's were placed primarily upon coin— cidence data, energy sums being somewhat risky. During the course of this study many other transitions and levels were suggested by the coincidence data and energy sums, but sufficient evidence was lacking to place these with a high degree of confidence. Figure 34 shows a level scheme of Pb203 showing additional transitions from the 31203 decay which could be placed on the basis of precise energy sums alone. The dashed lines indicate new states suggested by admittedly poor coincidence data plus energy sums while the semicircles indicate that some coincidence data supports such a placement for that transition. 3.2.5. Electron Data and Multipolarities The Y—ray intensities from the present measurements were Compared with the conversion—electron intensity data of Novakov et al. [N058], Fritsch [Fr56], and Stockendal [St60] in order to learn some- thing about the multipolarities of some of the transitions seen in the Bi203 a decay. The two sets of data (the present Y—ray intensi- ties and the previously published electron data) were normalized for m the pure M4 825.2—keV transition of Pb 203 . The conversion coef— i . We 3 . .l x 1 i 3 2 \I. . n; 0 I 1 g 1 .IL I. .1 but COUNTS PER CHANNEL 210 1 1 1 1 t 126—KEV GATE WITH BKGD SBTD 31 i: . 10 1 8 o i 3 1: 1 8 g 21 m co. m ' more 10 m 0 O" o 1 :2 :2: 1 sg !\ r-l ' 1 1 1” 101 1,111 1 .1 1'1. I 1" ...“!l: 1 1111111111111 1111111111 1111111 1111111 111111 1.. -.1 137-KEV GATE WITH BKGD SBTD . 1; I 7+. 1 to 1 U . tn 2' 1!) 1 10 1 c8 1 1011 1 ' ' 1 ‘ . I 1 u ‘1 1 1 1 , 1 I 1' 1 1; ‘ 1 ‘1 1 1 1 1 11111 186-KEV GATE WITH BKGD SBTD 1 1031 o 1 03 o I N: S 1 m (D 2. Lo I .7 co m 1 10 1 I a; dim 1 01 [\r—d 2 2': ”1 1 1 . ‘ 1 11 g g ' 101 “ . 1 - 11 N I i 1 ' 1 ' l 1 ‘ 1 ' I “f --:.53 . 1‘ _____ . 1111 1' .. 1 '1 0 50011000 1500 2000 2500 3000 CHANNEL NUMBER Fig. 33. The y—Y coincidence spectra from the Bi203 decay. The spectra were recovered from the coincidence data stored on magnetic tapes using EVENT data—taking routine. The titles of the coin- cidence spectra have the same meanings as those in Figure 24. / 102 JUZZ(T‘0 tune WFZDOO 211 l96-KEV GATE WITH BKGD SBTD Lm++momxomm w.mwN I 2|2—KEV GATE WITH 'BKGD SBTD szz1500 keV. A semicircle at the origin of a transition indicates some coincidence data support for such a placement. w N.N .Nwmfiflgt; ‘ :: o.mm_ N.m®»‘__ \ 236 ._ 92.». 35. 92.: hmwmm 98.. ..I Nde NKOm Ndmw. o. m__N mem N.NN _Noo. t...mmm. 0.0Nm w.Nwm_ 75ns l86-4 I26.4 0.0 S 6 .....ow.%2... _ _ «.83 3mm _- _ _ 1.16wa _ I...___II_. _ _ 33. ".l _ v.fl.~.,...__m_“l-=_I_ _ m.Nm¢ .mm._. hmm=nmflm___- . 2mm. _II_._l_-____ 0.0.: 52' Ila—2' nil—III Ill-Ell I _=I=I£!-=__ _ _ .%.w.___=_ .__—_=_.— 203 82 Pb (continued) 34. Fig. ’ W' ficient of thes coeffh in Tab used t multip impose calcul et al. errors ical I ity d; methm the B: on th 237 ficient used for this normalization was 0.217 [5165]. The results of these calculations (including selected theoretical conversion coefficients [8165])and the predicted multipolarities are listed in Table 14. The theoretical conversion coefficients were also used to construct smooth curves of M1, M2, M3, MA, E1, E2, and E3 multipolarities over a lOO—ZOOO-keV range, upon which I have super- imposed the experimental points (Figure 34). The error bars were calculated using the published errors for the electron data (Novakov et al. [N058], 115%, and Stockendal et al. [St60], i152) and the errors listed in section 3.2.3.A. for the y-ray data. Such a graph— ical presentation of the complicated Bi203 (and 312°”) multipolar— ity data is by far a much more efficient and more easily assimilated method of presentation than that of the table. While many more of the 31203 intense transitions are listed in Table 14 than in the corresponding BiZOL+ table (Table 10), it still is unfortunate that more electron data is unavailable, as this would make precise characterization of the spin and parities for the Pb203 scheme much more accessible. Several of the transitions listed in Table 14 (cf. Figure 35) have previously been assigned multipolarities on the basis of conversion—electron ratios and absolute conversion— coefficient measurements. These assignments and their relation to the assignments in this table are discussed below. The 825.2-keV transition is the transition associated m . with the 6.1—s i13/7 Pb203 state. The K conversion coeffic1ent of the 825.2—keV transition has been measured by Stockendal et s 31:: I huuafluuw humans: ughwnu neuuuhcnhh u sou—urban“ hnhl> Monuuiuvlk \l‘\ NOIWMHI: .§H Ifln‘k ¥l H'UiUIHOCIH huukIHOI u Iifldfll .IIOuuulclhu r Aswan no Muihl IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIA 000 defiance—woo l9: val—3a nun-um In: no usages—non.“ 133.50th :03. i n- uou 2:: 153305 2F. 63333.: t. 33: 333335 :33:qu H33: In: van-H31”. 39.093 523) 33.1)“ Anny: 080.3an Iona aquaauua nouuouaulk van-Hon... .833 3:333 3.8093 ...—Audi 32qu .— 328: ouauuuuuu loam 3010-3 255‘ India—33 nouuooafu 05:3» Iowa .5150 used!“ lam 33:33.: :7» 02339— 33 3.3.35. IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII .332 3 85» 3:33: .35 howl» we: 8.590.? 0:... 33.-Enos 3 «.03 I: {050304 Scum. Iona vow-1510 nuns—um; :2» a guuuononx «#330 E as: 3;: SIC: 3.3; 5-3.: I «.2 3.3 I n.3,: a H! uh HQ . I GIZA ATE; SIGN; 271.3 I Ne" 3.2 I 932 E «m I S «m G 2.3 QIZJ see... 2%: “Tons :TZAJTXJ «.2 3: as 532 N! H! mm NM . 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S S 8;: 8:4 “7:5 SIX; GIVE.» :Tvai :Iz.» ~.o~ 2:3 3.: is: S Q S E «m 836 2-1.0 :Ioma SIX.” :39: 3-33 0;: .82 3“ .32 S 2 S E i I I I :IVZM‘M «27:1: :Ivzsm 9% "8°: 82m «in k Cam: 533cm M a 53:35 53333 assume laud—z u a Hanan—003E. «mun—wanton” may-» “Saunas-N ”.3339; .nuouuuaauu > new: we hawk-Honwunnl .3” quack Io' I0° K52 0 I00 0 Fig. CELECTRON DATA FROM (N058) SAME AS - 150 200 300 400 500 700 IOOO ISOO 2000 35. ENERGY (keV) Experimental conversion coefficients for some Pb203 transitions. The smooth curves of the theoretical a were prepared from tables in [5165]. K al. [ This by 51 was t to tf al. I L-sm Fina good for assi pec 21 the 240 al. [St60] by the method of external conversion to be 0.24*0.05. This should be compared with the theoretical value of 0.217 given by Sliv and Band [3165] for an M4 transition of this energy. This was the transition (and multipolarity) that was used to normalize to the electron and y—ray data. The 126.4—keV y has been assigned an E2 by Novakov et al. [N058] on the basis of the measured (Ll + L2)/L ratio. The 3 L-subshell ratios given in [St60] also verify such an assignment. Finally, the 126.2—keV state has a bi of 75 ns [Be6l] which is in good agreement with the single-particle transition half—life [Le67] for an #2 of this energy. The present data also confirm such an assignment. Little need be said about the 186.4—keV transition. Both Novakov et al. [N058] and Stockendal [St60] reported an M1 multipolarity for the 186.4—keV transition based upon independent studies of conversion—electron ratios. However, Table 14 indi— cates an assignment of M1 or E3 on the basis of an a of 0.82 K (from [N058] electron data) or 0.39 (from [St60] electron data). The theoretical values are 0.51 and 1.2 for an E3 and M1, res— pectively [$165]. Novakov's electron data appear to predict the M1 while Stockendal's data seem to suggest an E3 assignment. If the previous investigations [N058,St60] are correct in the M1 assignment, then it appears as if Novakov's electron data is more precise. The 263.8—keV transition has previously been assigned Ml 1, i [N05 [St6 whet acte pres ing 0.M ass. but am ass COE trz 241 [N058] and M1 or M2 [Fr58] multipolarities. A third investigation [St60] calculated the dK whether the interfering 169.8—keV PbZO” L line is of M1 or E1 char— as 0.53i0.10 or 0.67i0.10 depending upon acter. The Pb20H 169.8-keV transition was shown to be Ml by the present study, thereby eliminating the 0.67*0.10 value. The remain— ing 0.5310.10 value agrees very well with the theoretical value of 0.46 for an M1 of that energy. All these data corroborate an M1 assignment for the 263.8—keV transition. The 381.3—keV transition had no electron data available, but the K—experimental conversion coefficient unambiguously suggests a multipolarity of M2 for this transition [St60]. The 820.2— and 847.0-keV transitions have been previously assigned E2 multipolarities on the basis of the measured K conversion coefficient and internal conversion ratios [St60]. The 820.2—keV transition assignment is clearly substantiated by the present study (cf. Table 14). In the 847.0—keV transition, however, a disparity be— tween the [NoS8] and [St60] electron data results. The [N058] data suggest an H2 assignment, while the [St60] data appears to imply E3. Considering the previous results plus the present investigation, the E2 assignment appears much more reasonable. Once again the Novakov et al. data seem to be slightly better than the equivalent electron data of Stockendal [St60]. Finally, the 1033.8—keV transition K/L conversion ratio was remeasured by Stockendal [St60] and found to be consistent with the M1 aSSignment previously suggested by Novakov et a1. [N058]. The present data also substantiate such an assignment (cf. Table 14). ton sior the of 1 pol.- Call the fou lie the WOU Sta (cf es! the luv 242 3.2.6. Spin and Parity Assignments for Pb2°3 As in section 3.1.6., I have used the experimental pho— 203 ton intensities for Bi , the calculated (or experimental) conver— 1203 sion coefficients of some B Y rays, the B1203 decay energy, and the Bi203 t% to calculate the percent feedings and log ft's to each of the states in Pb703. For those Y rays without reported multi— polarities, I assumed each was an M1 multipole (for the purpose of calculating log ji's only). Using the modified DECAY SCHEME program, the feedings and log ft's to each state were calculated; these are found in the left—hand column of Table 15. The validity of such a list is seriously questioned by the well-defined spins of the 126.4— and 186.4—keV levels. The 1/2— and 3/2- assignments would suggest highly—forbidden 8 transitions with their resulting large log ft's. A much more readily believed set of percent feedings and log ft's would result if the feedings to the 126.4— and 186.4—keV states were arbitrarily set to zero. This, not being unreasonable, (cf. section 3.1.6.) was done and the new set of values are found in the right—hand column of Table 15. This last set of values was used in establishing the external quantum numbers (i.e., spin and parity) of the levels in Pb203. 3.2.6.A. Ground, 820.2—, and 825.2—keV States The ground state has been assigned 5/2— by several former investigations [St6O,N058,D068]. This is also consistent with an odd nucleon (hole) in the fr /2 shell-model orbit. The l3/2+ assignment of the 825.2-keV state follows Excite: 121 18 82 82 86 89 103 ll( 243 Table 15. Percent feedings and log fT's for the excited states in Pb203. Excited state Percenta Log fia Percentb Log frb feeding feeding 126 1.87 8.68 0.0 large 186 2.28 8.58 0.0 large 820 6.13 7.94 6.39 7.92 825 14.8 7.56 15.4 7.54 866 1.50 8.53 1.57 8.51 896 3.63 8.14 3.79 8.12 I 1033 0.0 large 0.0 large } 1160 3.88 8.00 4.05 7.98 1547 4.10 7.78 4.28 7.76 1641 1.00 8.34 1.05 8.32 1802 1.51 8.06 1.58 8.04 2033 0.38 8.49 0.40 8.47 2184 0.0 large 0.0 large 2387 0.88 7.78 0.91 7.76 2568 2.86 7.02 2.99 7.00 2620 1.14 7.33 1.19 7.31 2667 18.1 6.04 18.9 6.02 2713 21.0 5.88 21.9 5.86 2748 1.38 6.99 1.44 6.97 2753 8.13 6.20 8.48 6.18 2793 1.26 6.91 1.32 6.89 2821 0.94 6.96 0.98 6.94 2964 0.24 6.95 0.25 6.93 3016 0.95 5.97 0.99 5.95 3045 2.01 5.32 2.10 5.31 :WW aCalculated values from relative beta intensities as determined from transitions populating and depopulating each state in Figure 31. bCorrected values after the relative beta intensities to the 126.4— and 186.4—keV states were arbitrarily set to zero. direc is cc lndee thet hard. side stat lev con Stu‘ mul t0 3/2 Prc ‘ the \ i 244 directly from the M4 character of the 825.2-keV y. This assignment is consistent with the assignments in references [St60 and N058]. Indeed, this was the transition and multipolarity used to normalize the electron and y—ray data in section 3.2.5. The log ft of 7.5 is hardly large enough for a first-forbidden unique transition. Con— sidering the difficulty of finding the y's populating the isomeric state, this is not horribly surprising. The 9/2— assignment of the 820.2-keV level was firmly fixed by the study of Pb203m by Doebler et al. [D068]. The E2 character of the 820.2-keV transition quite clearly suggests 9/2— through 1/2— assignments. The discovery of a 5.0—keV transition in Pb203m [D068] suggests that the 1/2— through 7/2— can be eliminated. The 633.8-keV transition between the 820.2—keV and 186.4—keV levels (cf. Figure 31) must then be an M3, which, being highly converted, makes it surprising that the previous conversion—electron studies did not report such a transition. 3.2.6.8. 126.4: and 186.4—keV States The 60.0—, 126.4—, and 186.4-keV y's have Ml, E2, and M1 multipolarities, respectively. The E2 126.4—keV transition suggests 1/2— to 7/2— for the 126.4—keV state. The.M1 186.4-keV transition suggests 3/2- to 7/2- for the 186.4—keV state. The large log ft's for these states probably rules out the 7/2— assignment. The M1 60.0—keV transition from the 5/2-, 3/2— 186.4-keV state would suggest 1/2— to 5/2— for the 126.4— keV state. Comparing the low—lying Pb203 excited states to those in Pb205 and to the shell—model level scheme in this region (cf. Chapter IV), it becomes apparent that the assignment for the 126.4— and 186.4—keV states shou] pr0p( othel to d 866. 1/2— siti an a pose resu bala tum 245 should be l/2- and 3/2-, respectively. These are the same assignments proposed by Novakov et al. [N058]. In addition, if the assignment were other than I have suggested, then one might expect to_see more transitions to these states from the high—spin high—lying states in Pb203. 3.2.6.C. 866.5-keV State No multipolarity data on any transitions to or from the 866.5-keV state are known. The state, however, does populate both the l/2— l26.4—keV level and the 5/2— ground state. Assuming the tran— sitions to be predominantly Ml, E], or H2, this would appear to suggest an assignment of 1/2', 3/2', 5/20, or 7/2l. The large log ft of 8.5 possibly suggests an allowed or first—forbidden transition and the resulting 7/2i, 9/2!, or ll/2i assignment. However, the intensity balance does not appear to be very good. This might mean that the log ft should actually be larger than it appears to be. These data lead me to possible assignments of 5/2' or 7/21 . If the 866.5-kev state were 7/2—, then the depopulating transitions would be Ml and M3 (for the 866.6— and 739.9-kvV y's, respectively); for 7/2+ they would be Hi and M3; and for 5/2+ Lhey would have to be Hi and M2, rospcctivclv. Branching rntios for these pnssihilitir-s «lo not correspond in wlml is founrl r-xpi-riml-ntnlly. 'l'll“ only runsnnnhlt- mmlgnmvni is ')/2?--. This would f{"l'ilrl' mull lpnlurlilns of MI nml M2 for the 866.6— and 739.0—kvV lrunsllluns, respectively. The hrnnchlug ratio is consistent if one allows for collr-ctivo enhancement of the 4'2. As a result, 1 assign the HYHLD uL 866.5—kvV a spin and purity of 5/2-. 3.2.6.0. 1033.6~kev State The state at 1033.6—keV has been previously assigned as 7/2- o 21 tra The 84 assign and SL i—ray suspe 1033. ulan able The Thes WOSt Sh 7/2— or 5/2— [N058]. Table 14 indicates that the 1033.7—keV Y is an M1 transition, thereby suggesting states of 3/2—, 5/2—, or 7/2—. The 847.0—keV Y is an E2 multipole and subsequently suggests an assignment of 1/2— through 7/2—. The log ft is arbitrarily large and suggests a highly forbidden transition. As only 380% of the 31203 y—ray intensity has been placed, the log ft value could easily be suspected. From the multipolarity data alone I suggest the 1033.6—keV state is 7/2—, with 5/2— still a possibility. 3.2.Q:E. 896.9— and 1160.8—keV States Only the strong 896.9—keV transition was found to depop— ulate the 896.9—keV state. Sadly, no multipolarity data are avail— able for this transition, i.es no electron data have been reported. The 8.1 log ft suggests an allowed or first—forbidden transition. These support an assignment of 7/2:, 9/2i, or ll/Zi. 11/21 can al— most certainly be ruled out if the 896.9—keV y can be assumed to be H2, M1, M2, or Ml. While I am tempted to reduce this to only the + parity assignments, to do so is uncertain and even dishonest. Be- cause no pOpulation of the 1/2— 126.4* or 3/2— [86.4—keV states is found, 1 think that i can safely assign 7/2l or 9/21 to the 896.9— keV state. If 9/2+ were a valid assignment, one might expect to see a transition to the 13/2+ state (which one does not). However, allowing for complex internal rearrangements, one cannot fully disregard such an assignment. The 1160.8—keV state assignments are based upon an M1 263.8—keV y to the relatively poorly assigned 7/2i, 9/2: 896.9—keV State. This obviously allows 5/2i, 7/2i, 9/2i, and ll/Zt. However, it is have this parit sugge ll/Zt thei stat 722. E2( bet 15/2 an 2 11/ ”El me '38 247 it is populated by strong transitions from higher—lying states which have ~ parity based upon their log ft's. While not an absolute test, this appears to suggest that the 1160.8-keV state is of negative parity although one cannot be absolutely certain. The log ft of 8.0 suggests, then, an allowed or first-forbidden transition or 7/21, 9/2i, or 11/21. The final assignment for these states is 7/21 or 9/2i. 3.2.6.E. 1547.6— and 1641.6—keV States These levels are included under a single heading because their only depopulating transitions are to the 825.2—keV isomeric state. The 1547.6—keV state has a single depopulating transition of 722.4 keV which has been determined (section 3.2.5.) to be either E2 or E3, depending upon which set of electron data one is willing to believe. These assignments would suggest 7/2—, 9/21, 11/2i, 13/2i, 15/21, 17/2:, or 19/2—. The log ft of 7.8 would appear to suggest an allowed or first—forbidden transition and values of 7/21, 9/2i, or 11/2'. Coupling these choices one is left with 7/2-, 9/2t, or 11/24. Having decidedly more confidence in the Stockendal [St60] electron data (on the basis of previous results) than in Fritsch's electron data [Fr56], I further reduce this assignment to 9/2+ or ll/2+. 7/2— can also be tentatively eliminated as no transition to the ground state is seen. If the 722.4—keV transition is a true U2 multipole and not just an M1 with a large admixture of collectively enhanced E2, then the assign— ment would be necessarily 9/2+. Uncertain of this,I leave the assign— ment as 9/2+ (ll/2+)- The 816.4—keV y depopulating the 1641.6—keV state has no assigned multipolarity. The log ft of 8.3 might suggest an assign— ment def it is 22 R931 for 0T ll/ 248 ment of 7/21, 9/2:, or ll/Zi. This state does not populate any of the well— defined lower excited states, but this would simply suggest that In is 211/2i. Owing to the undoubtly complex internal structure of many of these high-lying states, this is not really a good test for spin and parity assignments. Therefore, I shall leave well enough alone and retain an assignment of 7/2i, 9/21, or ll/Zi for the 1641.6- keV state. The 1802.4—keV state has three depopulating y tran- sitions, to the 7/2- (5/2—) 1033.6-keV state, to the 7/2— 866.5— keV state, and to the 5/2— ground state. These would (weakly) sug— gESt an assignment of 1/2— to 9/2—. No multipolarity data exist for any of these transitions. The 8.0 log ft is apparently allowed or first—forbidden. This allows an assignment of 7/2i, 9/2i, or 11/21. The — parity states cannot be absolutely excluded so I sug— gest the 1802.4—keV state is (in order of preference) 7/2—, 9/2- (7/2+, 9/2+) . The 2033.8~keV state has transitions to the 7/2— (5/2—) 1033.6—keV state and to the nebulous 1641.6-keV state. The log j? of 8.5 appears to imply an allowed or first—forbidden 5 transition, once again this suggests 7/2:, 9/21, or ll/Zi. The y transitions from this state tell me next to nothing, and any conjecture as to the nature of their multipolarities is certainly to be extremely tentative. Pessimistically, then, the assignment of the 2033.8—keV state is left as 7/2i, 9/2:, or ll/Zt. has thro only poor keV Thes Stat ilrin fort fofl or par are The tra 249 3.2.6.E. 2184.0— and 2387.8—keV States ‘ 1 The 381.3—keV y, which depopulates the 2184.0—keV state, has been calculated to be H2. This implies an assignment of 3/21 through 13/2'. The arbitrarily large log ft reveals nothing. The only remaining depopulating transition is the 542.9-keV y to the poorly defined 1641.6—keV level. The 569.4—keV y feeds the 2184.0— keV state from the 7/2—, 9/2— 2753.4-keV state (cf. section 3.2.6.M.). These data do not appear to be very conclusive, so the 2184.0-keV state is left as 3/2' to l3/2i. The 2387.8—keV state is assigned 7/2i, 9/21, or ll/Zi primarily on the basis of the log [L of 7.8 (allowed or first— forbidden transitions). The single depopulating transition goes to the 9/2+ (ll/2+) 1547.6—keV state, but this does not tell a great deal. 3.2.6.1. 2568.9—keV State The log ft of 7.0 could suggest an allowed or first— forbidden transition. This would mean a spin and parity of 7/2i, 9/2:, or ll/Zt. However, the two depopulating transitions are to positive parity states, and this would lead me to suggest that the transitions are Ml, El, E2, when coupled with the reasonably low log ft. The 7/21, 9/21, or 11/21 assignment is entirely consistent with such transitions. Nothing more can be said with much confidence about this state. 3.2.6.J. 2620.5— and 2748.7—keV States The 1800.3-keV transition to the 9/2— 820.2—keV state is fhh only 7 associated with the 2620.5~keV level. The log ft of 7.3 suggé form keV 7/2: the 1 the El 3 This an a 11/2 an. 250 suggests an allowed 6 transition (or possibly first—forbidden). Un— fortunately,this tells very little about the character of the 2620.5— keV state. The assignment must be left deliberately ambiguous, as 7/2:, 9/2i, or ll/Zi. The same arguments hold true of the 2748.7—keV state with the substitution of "1928.5—keV" for the "1800.3—keV". 3.2.6.K. 2667.8-keV State Of the six depopulating transitions of this state, only the 1847.6-keV y has been assigned a multipolarity (E2 or E1). The El appears to be correct although E2 cannot be absolutely excluded. This suggests (the transition is feeding the 9/2— 820.2—keV level) an assignment of 7/2+, 9/2+, or ll/2+ (or possibly 5/2—, 7/2—, 9/2—, 11/2—, or 13/2—). The log ft of 6.02, however, clearly suggests an allowed transition. (But note that Alburger and Pryce [A154] have suggested that in such a heavy nucleus allowed and first—forbidden transitions whould compete favorably.) On this basis and the realization that log fr's are not as sensitive a test as one might like to suppose, I propose an assignment of 7/2—, 9/2—, or 11/0~_ The reasonably strong 2667.8—keV y to the ground state (5/2—) also tight suggest the 7/2— and 9/2- as the mest likely assignments. The ro~ mainder of the depopulating transitions go to states which have assignments that are consistent with this assignment. Consequently ’ I assign 7/2—, 9/2- to the 2667.8—keV state. 3.2.6.L. 2713.4—keV State While five depopulating transitions are known for this state, assign1 indica to 5/2 it as ments. must I allow‘ estab multi POpul reSpe The 1 defil the; 9/21 \ cerl i i l l 311( toll state, only one (the 1893.3—keV y) has an experimental multipolarity assignment. If the 1893.3-keV y is a pure E2 as Table 14 appears to indicate, then, the spin and parity of the 2713.4—keV state is limited to 5/2— through 13/2—. The log ft of 5.9 almost conclusively labels it as an allowed transition, suggesting 7/2—, 9/2—, or ll/2- assign— ments. Unfortunately, no other data are available so the assignment must remain as 7/2-, 9/2—, or 11/2. 3.2.6.M. 2753.4—keV State The 6.2 log fL suggests 7/2—, 9/2—, or ll/2— for an allowed transition. Six depopulating transitions would normally establish the assignment of a level quite securely — if only the multipolarities were known. The strongest depopulating transitions populate the 7/2— (5/2—) 1033.6-keV state and the 5/2— ground state, respectively. This would appear to limit the spin and parity to 59/2— The remaining depopulating transitions go to levels that are too poorly defined to be of much value to the present assignment. Consequently, the 2753.4—keV state is assigned 7/2— or 9/2-. 3.2.6.N. 2793.7—keV State The 406.1-keV transition to the 2387.8—keV state (7/21, 9/2i, ll/Zi), and the 1245.9—keV y to the 1547.6-keV state (9/2+, ll/2+), certainly tell little about this state. The 6.9 log ft suggests an allowed transition, although first—forbidden cannot be strictly ruled out. At best, the assignment can be reduced to 7/2:, 9/2i, or 11/2i; l L f L transi at 282 Y s, x 6.9 f forbi ll/Zi adds 5"] 0] pola‘ no t Stat it n SUCl 252 3.2.6.0. 2821.1—z 2964.4—, and 3016.9—keV States Each of these states was placed on the basis of a single transition, well established through coincidence data. The states at 2821.1— and 2964.4—keV are depopulated by 2000.9- and 2144.2-keV I Y s, respectively, to the 9/2- 820.2—keV state. The log ft's are 6.9 for each state. This would suggest either an allowed or first— forbidden transition, thereby suggesting an assignment of 7/2i, 9/2i, ll/Zi for both states. The transition to the 9/2— 820.2—keV state adds no further information, as these transitions could easily be H1 or M1. However, it would be tempting to assume Ml multi— polarities, which would limit the assignments to 7/2-, 9/2—, 11/2—. One might also be tempted to rule out 7/2- and 9/2- on the argument that no transitions from these states Iced the 7/2— (5/2—) 1033.6—keV state. In lieu of the undoubtedly complex structure of these states, it might be reasoned that complex internal rearrangements hinder such possible transitions. To be entirely honest, I do not feel justified in reducing the assignment in this manner, so I conservative— ly leave the assignment of the 2821.1— and 2964.4—keV states at 7/21, 9/2}, or 11/2!. The state at 3016.9 keV has a single transition; it feeds the 1033.6—keV 7/2— (5/2—) state. This suggests 3/21, 5/2i, 7/21, 9/2i, and ll/Zi, not very helpful to be sure. The log ft of 6.0 would most probably limit the assignment to allowed transitions, or a state having 7/2—, 9/2—, or ll/2—. No additional information is available, so I cannot reduce the assignment further. to a 8 tensit keV st The 1( state consi ll/Z- conc thee leve ing Tm” raU 253 3.2.6.P. 3045.2—keV State The 3045.2—keV state has two depopulating transitions, one to a 820.2—keV state and a second to the 1033.6—keV state. The in— tensity ratio is 0.41/5.5. This would seem to suggest that the 3045.2— keV state should have an assignment of 5/2:, 7/2i, 9/2i, or ll/2i. The low log ft of 5_3 almost certainly rules out the positive parity states. The low log ft also would rule out the 5/2~ state. The consistent assignment would therefore appear to be 7/2—, 9/2— or ll/2—. 3.2.6.Q. Comments This last section on spin and parity assignments necessarily concludes the B1203 experimental sections. The theoretical or semi— theoretical discussion of the meaning (or "so what") of the Pb203 level scheme is left to a later chapter (Chapter IV ). The remain- ing comments on the Pb203 investigation are identical to those found in the last section on the PhyoJI experimental results; and rather than repeat them here one should refer to section 3.1.6.V. for the appropriate details. funda is t( I mi; sign: catei (Cha cove then pres flom thr( Clo: rep the mat mod PIE are CHAPTER IV DISCUSSION OF RESULTS As I implied in the introduction to Chapter I, one of the fundamental functions of experimental nuclear and particle science is to provide a detailed test of the current nuclear models. Perhaps, I might even be naive enough to hope that the present study would significantly contribute to the formulation of a new, more sophisti- cated, more comprehensive nuclear model. The experimental chapter (Chapter III) has already described the "wealth" of information un— covered by the present investigation. It is frightfully tempting, then, simply to close this thesis with an impressive comparison of the present data with the previously reported results — and, with a flourish, quit. If anyone has had the stamina and fortitude to ”wade" through Chapter III, he certainly does not deserve such a fate. Such a closing would also leave the inquisitive reader with the anticipated "so what". The content of this chapter is designed to tie reply of the loose ends together, and to attempt some, albeit simple, expla— nation of the 31203 and BiZOL+ decays in terms of the current nuclear models. In section 4.1. a deliberately cursory comparison with the previously reported results is presented. The shell—model discussions are found in section 4.2. Section 4.2.1. discusses the nuclear shell— model level spacings near Z=82 and N=126 in the Pb isotopes. Sections 4.2.2. and 4.2.3. also deal with the 91.203 and Pb?“ level schemes, 254 255 respectively, in terms of the current models and previously performed calculations. Section 4.3. is what might be called the Grand Finale, i.e., a final summary of the topics covered in this thesis, and a few proposals for future investigations. 312m» elect energ the p trans elude The e these 90.9 not 143) Stoc litt 256 4.1. Comparison With Other Investigations 4.1.1. Pb20# Experimental Data The two previous major investigations [St58,Fr58] of the BiZO” s decay utilized high-resolution permanent-magnet conversion- electron spectrometers. Excellent transition energies in the low energy region (<1.0 MeV) were obtained and are in good agreement with the present values. Rather than list all 67 previously reported transitions, I would refer the reader to reference [Nu65] which in— cludes a compilation of the results from both of these investigations. The electron data (i.e., K and L relative electron intensities) for these transitions can also be found in Table 10. Only the 78.6—, 90.9—, 92.2—, and 368.0—keV transitions previously reported were not found in the present study, though many more were added (some 143). Also, inasmuch as the tentative decay scheme proposed by Stockendal et a1. [St58] was based almost entirely upon energy sums, little can be gained by a detailed comparison with the decay scheme proposed in the study. The changes (and primarily the additions) made in this decay scheme by the present study have already been discussed (section 3.1.4.) and will not be rehashed here. Rather tragically though (fortunately for me however), this will be the first reported investigation of the 8120” y rays specifically, and no data exist for this comparison. It is rather interesting, however, to compare the results of recently reported scattering data with the present results. Hol— land et a1. [H069] have investigated the Pb206(p,t)Pb20“ reaction and r (cf. veale to th inves luti< none perh vest ing thes lea] revs Dos Par 257 and reported 15 excited states. These are tabulated in Table 16 (cf. Figure 23). Also, tabulated in Table 16 are the states re- vealed in the B120” a decay which apparently are equivalent in energy to the (p,t) data. Quite remarkable agreement is evident. One other investigation [Re67] has reported data on the same reaction. The reso— lution was significantly poorer and very few states were reported — none of additional significance. A third group [Bj67] has reported performing a Pb202(d,d')Pb20” reaction. The results of their in— vestigation are also included in Table 16. It is rather intriguing to note that they report a new state at 1.353 MeV. In neither (p,t) study nor the present a decay study has this state been seen. A re— investigation of the (d,d') reaction might well be in order — hope— fully, to confirm such a state. At present DWBA calculations are be— ing performed [H069] to determine the spins (and parities) of some of these states accurately. It should be quite rewarding and exciting to learn of their results, as a more detailed comparison with the states revealed by the decay of Bi20L+ should then be possible. 4.1.2. Pb203 Experimental Results The several investigations of Bi203 already discussed [N058,Fr58,St60] have revealed a wealth of information about the Pb203 excited states, their associated transitions, the spins and parities of these excited states, and some about the multipolarities of a few of the Pb203 transitions. For an excellent summary of the previous B1903 data one should consult reference [Nu65]. The previously pro— posed decay scheme and the multipolarity data have already been com— pared earlier and will not be repeated (cf. section 3.2.5.). Rather 258 Table 16. Comparison of Pb204 excited states revealed by scattering reactions with those of present study. E (MeV)a E (MeV)b E (MeV)c E (MeV)d scatt scatt scatt E 0.0 0.0 0.0 0.0 0.899 0.90 0.90 0.899 1.274 1.27 1.27 1.274 _ _ 1.353 — 1.569 1.56 1.5 1.563 1.663 — — 1.720e + 1.727e 1.824 - — 1.817 1.932 - , — 1.936 2.173 ' — — '2.185 2.267 2.2 2.268 2.258 2.482 - - 2.480 + 2.506 2.642 — 2.630 — 2.831 2.8 - ~ 2.898 — — 2.9128 + 2.920 + 2.928 3.139 - - 3.170 3.246 — - 3.232 3.461 - — 3.461e -——— “rm aEnergies from Pb206(p,t)Pb20” reaction [Ho69].The reported energy error was 125 keV. 259 Table 16. (continued) I bEnergies from Pb2°5(p,t)Pb201+ reaction [Re67]. cEnergies from Pb20“(d,d’)Pb20L1L reaction [Bj67]. d 204 r, Energies of szou excited states revealed by a decay of Bi (present study). eExcited states suggested, but not confirmed, in the secondary , PbZOk level scheme (Figure 25). sadly, 01 Bjerrega; action. are the i spond to agreemen sive res] be rathe to think stead, 1 known ab and prec taken. 260 sadly, only one scattering reaction producing Pb203 has been reported. Bjerregaard et a1. [Bj67] have investigated the Pb20”(p,d)Pb203 re— action. Their results are tabulated in Table 17. Also tabulated are the states revealed by the present study which most likely corre— spond to their reported states. While not extensive, quite close agreement is evident. DWBA calculations were attempted, but inconclu— sive results were reported with no new spin assignments being made. The comments made in sections 4.1.1. and 4.1.2. seem to be rather perfunctory but enlightening — and so they are. I would like to think that this is not necessarily the fault of the author. In— stead, it points up the fact that comparatively little was actually known about the Pb203’20H excited states and related y—ray transitions, and precisely for this reason'was the present investigation under- taken. ._ 261 Table 17. Comparison of Pb2°”(d,t)Pb203 scattering data to the present study. EScatt (MeV)a EE (MeV)b 0.0 0.0 0.12 0.126 0.19 0.186 0.82 0.820 + 0.825 1.03 1.034 1.56 1.547 2.25 — 2.77 2.748 + 2.753 a Taken from reference [Bj67]. Energies have reported error limits of $0.02 MeV. b Energies from a decay scheme proposed in the present study. 4.2. Sh shell-mod presented have used residual and confi in severa was obtai siderably results a of Pb205 interest light of szo“ and Pb205.2o 262 4.2. Shell-Model Characteristics of the szoq and Pb203 Level Schemes While neither extensive nor intensive, a cursory treatment of the shell—model calculations on the Pb207’206’205 isotopes has already been presented in the Introduction (Chapter I). In short, these calculations have used the experimental single-hole energies of Pb207 plus various residual interaction potentials (i.e., nucleon—nucleon interactions) and configuration mixing to calculate the theoretical energy levels in several Pb nuclei near szoe. For Pb206 quite excellent agreement 205 was obtained, but for Pb the calculations have already become con- siderably more sensitive in the theoretical evaluation and the results are comparatively lousy. Perhaps, the present re-investigations of Pb205 [K070], szou, and Pb203 at MSU will rekindle serious theoretical interest in these Pb isotopes and lead to their re—examination in light of the current nuclear models. Having nearly completed the experimental investigations of szo” and Pb203, I soon began to consider the characteristics of the Pb20'“203 level schemes in terms of the several nuclear models of in- terest (the shell model, the collective vibrational model, and the quasi—particle model). With trepidation and yet a certain boldness, an attempt was made to "analyze" the results of Chapter III. After sev— eral unsuccessful bouts with the shell and collective models, it grad— ually became apparent that these decays are quite unwilling to yield their information so easily. This meant that the present discussion is considerably less detailed than originally hoped. However, it is hopeful that the present experimental investigation and brief theo- retical p1 few guide] these isoi "equal til Actually , While not appears t taken . lective thege m shell 0: 263 retical presentation will lay a new foundation and, perhaps, suggest a few guidelines for a reconsideration of the fundamental structure of these isotopes. As szo“ was the first to be experimentally investigated, "equal time" requires that the Pb203 level scheme be discussed first. Actually, the reason for taking Pb203 first is not nearly so naive. While more work of a theoretical nature has been done on szou, Pb203 appears to be far simpler and, therefore, more easily described. Once Pb203 is completed, the more difficult Pb‘Q-OL+ level scheme will be under— taken. 4.2.1. Nuclear Level Spacings in the Pb Region near Pb203’20” Previous theoretical studies have shown that it is possible to explain some of the experimental information in the Pb isotopes by using either pure shell-model calculations or by modifying them by the inclusion of collective-motion terms. It is fairly evident, though, that because of the hole—hole residual interactions and the config- uration mixing as well as other difficulties, shell-model calculations advanced by Kisslinger and Sorensen [Ki60] appears to avoid some of these difficulties (details will be discussed in section 4.2.3.), and are more easily handled from a strictly qualitative viewpoint. For the most part, the present discussion will be confined to a dis- cussion of the decay characteristics in terms of the shell and col- lective models. In attempting to assign the shell—model configurations in these nuclei, one first must know the nuclear level spacings of the shell orbits. The spacing of the ground and first two excited states in the adj: proton coni ground and spins of l, the shell-1 immediatelj 264 in the adjacent odd-mass Tl isotopes gives one some idea of the single- proton configurations near the Z=82 closed shell. Figure 36 shows the ground and first two excited states in the odd-mass T1 isotopes. The Spins of 1/2+, 3/2+, and 5/2+, respectively, are consistent with the shell-model assignments, 81/2’ d , and dS/z. The two states 3/2 immediately above the Z=82 closed shell are the kg and f7/2 orbitals; /2 this can be determined from the ground and first excited states in B1209, which has a single unpaired proton outside the Z=82 closed shell. For neutron numbers just below the N=126 closed shell, the odd neutron (in Pb203) can populate the fg/O, pl/Z’ pa/z’ i13/7, f7/2, or h orbits in the ground or low—lying states. The large pairing 9/2 energy of the i orbit forces neutrons to fill it in pairs and not by 13/2 odd particles (perhaps the reason why no i ground states have yet 13/2 been observed). Examining the systematics of the better—known odd-mass isotopes having a closed Z=82 shell and an unpaired neutron, one can get some idea of the ordering of the shell-model orbits in this region. These systmatics (Figure 37) indicate that most probably the neutron states (i.e., holes) are, in order of increasing energy, fS/z’ p3/2, and pl/z. Figure 38 shows a compilation of the experimental and theo- retical data for the fS/z’ ps/Z, and pl/2 neutron level spacings in the lead region [Be61]. The quasi-particle calculations of Kisslinger and Sorensen for Pb203 appear (Figure 38) to predict an order of f5/ , 2 p3/2, and p1/2‘ However, it is apparent from Figures 37 and 38 that the spacing between the pq/O and p3/2 is probably small in Pb203, as the qualitative quasi-particle calculations indicate an inversion of these orbitals quite near szoa. As experimental systematics are, El 0 O O O 0 0 O O O O O 5 4. 3 l O O O O 7 6 2 «>08» \Iwmmzm 265 J) O O ENERGY (keV) w . o 0 DJ 0 O IOO |93 |95 i9? I99 ZOI 203 205 AT} Fig. 36. Systematics of the low—lying 1/2+, 3/2+, and 5/2+ states in odd—mass Tl isotopes. These should be relatively pure 3. 2, d3 2, and d 2 shell—model states {Do70a}. l/ / 5/ I000 900 800 700 O O O O 0 0 4 6 5 Q/mwxv \xmvmmzm 266 .q 0 O) O ENERGY (keV) O I97 199 ZOI 203 205 207 APb Fi . 37. S t t' f the d i ‘ g ys ema 1cs o fS/z’ pl/Z’ p3/2, an 13/? states in the odd—mass neutron-deficient Pb isotopes [Do70a]. Fig. 38. 7% Wm '5/2 (Pb) am am «m «N ‘ N1 113 . 115 Compilation of experimental and theoretical data for the and pl/2 neutron level spacings in the lead region [Be61]. Thur x mm or and S roman I b Elporlmnnl Information 1 . [( /, )"(1/2.‘)P]°_(m /. ’ I17 119 121 123 125 267 A! KoV Erratum-nut Intonation ' I ...: I I l l , ~ 1 5 I ”on, 15/2 (1:11.119)j [<1/,-)n(1/2np]°_(m . , 1 i .2003 . _____ J / I . ‘1 —- —.__‘ 5 ‘ 1 [1 MeV and <2.6 MeV) are nearly untouchable by the present discussion. Nothing distinguishing marks any of these states, and until more data are obtained to narrow down their spins and parities, nothing of considerable value will be forthcoming. The transitions to the high-lying states (which have poorly defined spins and parities) do have low log ft's, In fact, all states >2.65 Me Figure 3 the very sition. to thes: specifi‘ and them vetted that is 2.77 Me With 3. a poss: forbid the 30. [A154] 278 >2.65 MeV have log ft's <7.0, and three states have values <6.0 (cf. Figure 31). The highest state placed by this study, 3045.2 keV, has the very low log ft of 5.3. This certainly implies an allowed tran- sition. In the succeeding paragraph several possible 8 transitions to these excited states are suggested, but final assignment of a Specific transition to a specific level must await more experimental and theoretical data. One possibility was that the h9/2 proton was being con— verted into one of the neutron orbitals above the N-126 closed shell, . . 207 that is, the 99/2’ ill/2, or g The 99/2 orbital in Pb lies 15/2‘ 2.77 MeV above the pl/2 orbital (which closes out the N=126 shell). With 3.2 MeV of decay energy such a transition appears to be a possibility. However, a pkg/2 + vg9/2 transition would be first- forbidden and should not have such a low log ft as 5.3 or 5.9 (for the 3045.2— and 2713.4-keV states, respectively). Alburger and Pryce [A154] have suggested (without proof) that in such a heavy nucleus allowed and first—forbidden transitions should compete favorably. This might mean that one of the low log ft transitions may go by such a transition, but almost assuredly not any transitions having log ft's <6. Similar reasoning might be used for a nh9/? + vi11/7 tran— sition, while the uh / + v' transition should not be seen at all 9 2 J15/2 (a second-forbidden unique transition). These transitions may account, then, for a couple of the middle—log ft range states. Sadly, no systematics of adjacent nuclei are available to allow one to place accurate energy limits on these various transitions. A third possibility is best explained in terms of the Kisslinge model th( Fermi su exists f closed 5 neutrons even the Conside could h the nhg ft stat its wa\ could 1 likely figura and expe 279 Kisslinger and Sorensen quasi—particle model. According to their model there is a finite probability that the orbitals below the Fermi surface may be unoccupied. This means that some probability exists for finding holes in the'hg/2 and f7/2 orbitals below the N=126 closed shell. Conversely, there is some noninteger probability that neutrons exist in the orbitals above the Fermi surfaces. In addition, even the simple shell—model predicts h9/2 and fg/Z holes at high energies. Consider the h9/2 proton of B1203. The most favored transition one could hope for would be a nh9/2 + th/z‘ This would be possible if the nh9/2 is converted into the vhg/z quasi—particle. One of the low log ft states very likely has a large portion of such a configuration in its wavefunction. Along the same line of reasoning, the transition could be the allowed (Z—forbidden) transition - nh9/2-+ vf7/2. Very likely one of the high—lying excited states has such a dominant con- figuration. One last case might be suggested. If enough energy is 203 available it is possible to convert an internal d proton of Bi 3/2 to a f5/2 neutron in Pb203. A first forbidden transition to be sure, but it should complete favorably with the slower allowed transitions in the heavy elements [A154]. Such a transition might be represented (mg/plddalz)“ . (Vf5/2)1(nh9/2)1 (nag/9'1. 4.2.2.C. Conclusion The foregoing discussion has been admittedly qualitative and cursory. However, until more data of both a theoretical and experimental nature are available little can be said with much cer— w tainty 1 ' Pb203 E hardly laid fo ‘ Bi203 d As it w ing the of suct ‘ a surve bYafe lized 1 Expect; case 01 can be in pb2l 280 tainty concerning the characteristics of the 8 transitions and/or ” Pb203 excited states. I fully realize that such an evaluation is hardly sufficient — but — perhaps, a foundation and stimulus has been laid for future re—evaluation of this isotope. 4.2.3. Discussion of PbZOL+ Results Having made some qualitative predictions concerning the Bi203 decay, it is now time to return to the more difficult BiZO”. As it will turn out, little can be said with much confidence concern ing the shell—model configurations of PbZO” excited states. In lieu of such assignments this discussion also includes (section 4.2.3.A.) a survey of the previous theoretical calculations on szou, followed by a few qualitative predictions. 4.2.3.A. Shell—Model Calculations on Pb20H The earliest shell—model calculations by True [Tr56] uti- lized the theory of Alburger and Pryce [Pr52,A154] to predict the expected energy levels in PbZO“. Pryce [Pr52] suggested that in the case of the two—hole Pb206 the energies of the single-hole states can be taken to be the energies of the low-lying single-hole states in Pb207. The single-particle states then combine (in Pb206), in the first approximation, to give a set of degenerate states with an ener- gy equal to the sum of the Pb207 single-hole states. Because of nucleon—nucleon interactions, the degeneracy is removed and the states are split, some being raised in energy and some lowered in energy. Pryce did not calculate this interaction explicitly but, using a zero—range nuclear force of pure singlet exchange character, al empir levels 2 uration: the sam energy : the sen reporte was not some 49 tion (a 281 he "estimated" the interaction parameters by a rough empirical method. Explicit configuration mixing effects were also estimated by addition— al empirical adjustment. True used this same method to calculate the levels in szou by assuming that the states are based upon config— urations of four neutron holes, where each hole in Pb201+ will have the same energy as the analogous single—neutron hole in Pb207. The energy shifts in each set of degenerate states were estimated using the semi-empirical two-particle interaction parameters previously reported by Alburger and Pryce [A154]. Configuration interaction was not included in his preliminary calculation. Figure 40 shows some 49 distinct levels calculated by True below 2.5 MeV of excita— tion (arranged by spins). The principal success was the prediction of the 9— state at 2.05 MeV. This compares well with experimental 9— state at 2185 keV. An unpublished recalculation (cited in [St58]) of True's energy values (but using new interaction parameters) has been performed by Blomquist, but at this time it remains a mystery as to which set yields better results. Using a nuclear model patterned after the BCS supercon— ductivity theory, Kisslinger and Sorensen (KS) [Ki60] have also cal- culated the levels of PbZO”. Their quasi—particle model idealizes the residual interactions between nucleons as a pairing force (the short-range force) plus a long—range quadrupole force. Using the Pb207 neutron single—hole energies to establish their parameter choices, they were able to predict many excited states in szou. These are graphically depicted in Figure 41. Several additional investigations [Ri64,Ri63, and Kr68] have been patterned after the Kisslinger and Sorensen quasi—particle Mmq EwaMmfl Spin—.Ol23456789 2168 "l——9- E5 1.274 41 E2 9 l/2°/o M3 Fig. 40. The energy levels of szo“ calculated by True [Tr56] according to the model formulated by Pryce [Pr52]. 5.0 uwzf ‘ 9 l[3/2 17/2 1 1 3.0 (us/212 93’? "He/H, I W2 W2 ‘— pvzrwz 1 : p3/2 .13. 2 f—‘ 3 ——_/ . [32Hy2/—‘_ j 20 2 pm .13/2 f- (93’?) —1 _q'eo—[T , + MeV l f5/2 p3/2, ‘ («a/212 p; 2 93/2 I [O (pl/2') pl/Z f5/2 it: | 12% L_~@x_~t_t._x__;_e_l_ O ' 2 3 4 5 6 7 8 9 IO [2 204 Pb Angular Momentum Fig. 41. The energy levels of Pb20“ as calculated by Kisslinger and Sorensen [K160]. On the left are the labeled un- perturbed states. For each Spin the horizontal line to the left gives the energy of the state; the second horizontal line Shows the effect of the inclusion of the P2 force. The lines to the right are a few experimental levels. The level marked [2+] is the collective 899.2— keV level. model at culated pb206 ,2 was lar approxi The lar the exa (for th in whit Sorens€ used a ing fo: P2 for range that 0 toward and p, Wheres Spin f diets 283 model and/or pairing model. Richardson and Sherman [R164] have cal— culated exact eigenstates of the pairing force Hamiltonian for the Pb206’2°“’202 isotopes. They also used an interaction strength which was larger than that used by Kisslinger and Sorensen, who used the approximate BCS theory of superconductivity to study the pairing model. The larger interaction strength used by Richardson and Sherman plus the exact solutions appear to lead to an error only 1/3 as large (for the states involved in the szoqm decay) as in the calculations in which the weaker pairing interaction was used (Kisslinger and Sorensen). The second investigation, by Kriechbaum and Urban (KU)[Kr68] used a model closely resembling that of KS. They also used the pair- ing force as the short—range component but instead of a quadrupole P2 force they used a quadrupole pigs octupole force as the long- range component. The results are not substantially different from that of KS, except that the states appear to be slightly perturbed toward lower energies. It is interesting to note the f5/2’ p1/2’ and p3/2 level spacings predicted by such a calculation (Figure 42). Whereas the KS quasi—particle model predicts a 5/2—, 3/2-, and 1/2- spin for the low-lying states in Pb203, the KU model correctly pre- dicts 5/2-, 1/2—, and 3/2- spin sequence experimentally observed. One last theoretical paper needs to be mentioned. Hader— 206 mann and Simonius [Ha67] have calculated the energy levels of Pb and PbZO“ using a delta force to approximate the residual interactions. The long-range force is assumed to be included in the mean potential and was not explicitly calculated. The energies and transition rates are calculated using the quasi—boson approximation [Ha67], which is strictly Fig. 42. 284 Theoretical neutron level spacings in the lead region, as calculated by Kriechbaum and Urban [Kr68]. Residual inter— actions were approximated by a short-range pairing force and a long—range quadrupole plus octupole force. The small black dots are the theoretical values. The large open circles are experimental values. exact fo tion was culated theoreti origina descrip general was to energy proble 0f the COHCEI invest 285 exact for only 1 pair outside the closed shell. The szou calcula- tion was only briefly touched, and the correlation between the cal— culated and experimental energy levels was not terribly good. For a more complete understanding and appreciation of the theoretical calculations mentioned, one should really return to the original papers. It was not the intention to present a detailed de5cription of each of these methods, but rather to summarize the general content of the theoretical attempts on the PbZO” level scheme. What it does point up, however, is how relatively little hag been done on light—lead isotopes. Once again, the original plan of action was to include a correlation between the experimental data and the energy levels predicted by the various methods and models. Two problems precluded this correlation. First, the spins and parities of the Pb20” excited states are far too ambiguous to say anything concerning these levels with much confidence. Second, the present investigation, as well as those preceeding, seem to indicate that one of the basic assumptions in these calculations is "all wet". Each of the forementioned has assumed that the singleehole energies of the Pb207 single—neutron hole states are good representations of the single—neutron holes in the szos—ZOZ isotopes. Considering the theoretical evaluations of the level spacings ([Ki60,Kr68]) and the Pb odd—mass isotope systematics (Figure 37), this does not appear to be a valid assumption. Rather, one should use the single—hole energies of the isotope of interest, or, at worst, the adjacent isotopes. Table 19 compares the single—hole energies in Pb207 to the hole—particle energies (for analogous states) in Pb203. 1. | .5 Tabl 286 Table 19. Single-hole energies in Pb207 and szos.‘ Hole Pb2°7 Pb2°3 configurationa energy (keV) energy (keV) (pl/2)"1 o 126 (1"5/2)‘1 570 o (pa/2)” 900 186 (1:13/2)—1 1634 825 (307/2) '1 2350 1034 W aAll paired nucleons (neutrons) are ignored in the configuration. A re-eValuation of these calculations in terms of this new set of values would be most welcome here. Actually, it is not quite this simple. The states in Pb203 are really five-hole states. Although four of these presumably do tend to remained paired, they still could affect the ”single—hole" energy. In other words, a "single- hole" state in Pb203 is not perfectly a single-hole state, but will be perturbed a little from the true ”sz03 single—hole" position. This is what complicates the calculations so - the Pb207 single—hole energies are not good for this region, the "single—hole" energies for Pb203 from above are better, but what is really needed are the true single-hole energies for Pb203. Perhaps, a re-evaluation of these calculations with the "single-hole" energies in Table 19 would still be fruitful. I I are be consid great ground has p] ton 01 N=126 just' havn POSS 4250 312C the 287 When the time comes that the spin and parity assignments are better—defined and the theoretical calculations have been re— considered, then a correlation such as proposed earlier would be of great interest. 4.2.3.3. Pb201+ ExCited States and Bizou B Transitions One first needs to estimate the configuration of the B120” ground—state spin. Using atomic beam experiments the ground state has previously been shown to be 6+. 3120” is a nucleus with one pro— ton outside the Z=82 closed shell and five neutron holes in the N=126 closed shell. From section 4.2.1. the order of shell orbits just below the N=126 closed shell was found to be fb/z’ p1/2’ p3/2, i13/2’ f7/2, and h9/2' I assume that the extra proton is in the “kg/2 level (in analogy with stable B1209) and that the unpaired neutron is in the f shell. By a theorem due to Kurath [A154], the 5/2 lowest state of a configuration with one proton in a level j and one neutron hole in a level j' is the one with Iej+j'-l, which in the present case is 9/2 + 5/2 -1 =6. The parity is even, leaving a 2014. configuration of [(wh9/2)(vf5/2)]6+ for the ground state of Bi , this is in agreement with experiment. The e decay should, therefore, go preferentially to states having spins of 5+, 6+, or 7+, in szou (if these are energetically possible). Only one transition to an excited state in szou appears to be reasonably fast in the e decay, a transition to the state at 4250 keV, with a log ft of 6.0. Consider now that the 83rd proton in BiZO” is in the pkg/2 shell. Also, consider the shells (orbits) above the N=126 level. From Figure 39 these are g9/2,i11/2, and le/Z' A very an hg/ “jls/z (uniqu almost The.re both 1 were. These sitio hole. M'“ 'l 288 A very plausible s decay transition.could take place by converting an h9/2 proton into a neutron in one of these levels. The nh9/2 + vle/zor vd5/2 transition would necessarily involve second—forbidden (unique) and first—forbidden (unique) transitions. Thus, these are almost certainly out of question when one considers a log ft of 6.0. The.remaining transitions, n h9/2 + vgg/2 and "kg/2 + Vill/Z’ are both first—forbidden transitions and also should not be so fast. The two possible 8 transitions which do appear feasible 1 were discussed in section 4.2.2.B. when the Bi203 decay was discussed. These will only be fleetingly re—mentioned here. One possible tran- sition was converting the pkg/2 proton into a neutron to fill the (Vh9/2)'1 hole. The second suggested transition involved converting an in— ternal wd3/2 proton into a vf neutron. Such a transition would 5/2 result in a proton broken pair state and would be expected to lie high, but just how high only more calculations will reveal. In Pb206 Alburger and Pryce [A154] suggest that an analogous transition occurs to states around 23.3 MeV. Perhaps the 3170.0-keV state is populated by such a transition. This is all that will be said concerning the 8 transitions, as anything further is purely conjecture and cannot be substantiated by evidence at this time. The Pb20” excited states are also only poorly understood. The 0+ ground state has the configuration (vf )2 as would be an- 5/2 ticipated (from the shell—model) for this even—even nucleus. The first excited state at 899.2 keV has a spin and parity of 2+. Kiss— linger and Sorensen have shown that this state is collective in nature state. gation in the prior states 1562.E predi‘ some] the g nearb 289 nature and as such should correspond to a one—phonon vibrational state. This was not totally unexpected inasmuch as several investi- gations [Kr68,Ri64,Ki60] had shown that there existed an anomaly in the 899.2—keV state. (In spite of the criticisms I aimed at the prior theoretical investigations, they did find that all the szoum states including the second 4+ state, were predicted reasonably well except for the "peculiar" 899.2—keV state.) Only the three remaining states in Pb20qm (at 2185.4, 1562.8, and 1273.9 keV) are sufficiently well-defined to make any predictions. Following the arguments of Kisslinger and Sorensen some possibilities can be advanced. From simple shell—model theory the 9— state necessarily involves the i13/2 state,as this is the only nearby orbit which can yield a negative parity for this state. The most obvious configuration would be a [(f )3(i )‘1]9 ; or in 5/2 13/2 or in other words, an i and an f quasi—particle coupled 13/2 5/2 to their maximum value. The 9- 2185.4-keV state decays into two 4+ states by a 0.912 and a 0.622 MeV E5 transition. The quasi—particle calculations of Kisslinger and Sorensen suggest that the 1273.9-keV state is composed mainly of two fg/z quasi-particles, while the 1562.8- keV state is mainly one f5/ and one p3/2 quasi—particle. As these 2 lie so closely in energy one might well expect an admixture of these configurations due to mixing. On the other hand, True [Tr56] claims that the 1273.9-keV 4+ state is composed of 72% (pl/2)2(p3/2)(jE/2) and 28% (pl/2)2(f )2. However, until further theoretical data 5/2 become specif but be differ states scatte one W( duced A nmm revea might 290 become available these assignments must certainly remain tentative. The remaining 25 excited states will not be assigned Specific configurations, not for any lack of possible assignments, but because one could assign any hypothetical configuration to many different possible states. Before abandoning the Pb20” excited states, some mention should be made of the previously published scattering data, particularly the (p,t) reaction. In such a reaction one would expect to see excited states in szo” which could be pro— duced by simply "plucking” pairs of neutrons from various orbitals. A number of the states revealed in the (p,t) reaction [H069] are also revealed by the BiZO“ e decay. Some of these possible configurations might be (_7“5/2)'2(X)'2 where X = pl/z’ p3/2’ i13/2’ f7/2, or hg/z' Other excited states of Pb206 from which a neutron pair could be "plucked” out are also possible, but listing all these tentative configurations does not lead one very far. Suffice it to say, that the excited states of Pb20L+ are sufficiently complex that no single configuration is likely to be assigned at this time with much con— fidence. spem schex and s doub] data Progr SOphi the i compl 291 "4.3. General'summagz During the present investigation high—resOlution y-ray Spectroscopy has been employed to study the very complex 8 decay 1203 204. schemes of B and Bi A fairly detailed Introduction deals with the characteristics and structure of each of the Pb isotopes as one moves from Pb208 (a doubly—closed shell nucleus) to Pb203. Somewhat lengthy for a tra- ditional introduction, it thoroughly "sets the stage for a discussion and subsequent investigation of the characteristics of Pb203s20#. Theoretical, as well as experimental, data are taken under consider- ation. A rapid survey of the apparatus and methods utilized for data acquisition and reduction is given. Several routine computer programs (TAKE CARE, VALTAVA, and COINPLOT) are introduced. Hardly sophisticated, they are nevertheless, samples of (and solutions for) the inordinate difficulties encountered in the construction of very complex decay schemes (such as those of B1203 and 3120”). The versatility of y—ray spectroscopy in studies of the behavior of nuclear states is evidenced by the Bi203’201+ decay schemes formulated in this investigation. Some 210 and 147 Y rays were iden— tified in the Bizol”203 decays, respectively. In addition, 60 y-rays were placed between 30 excited states in Pb20” comprising almost 90% of the photon intensity. In the B1203 decay scheme 51 y-rays were placed between 25 Pb203 excited states, including >80% of the photon intensity. Supplementary decay schemes show additional transitions which can be placed on the basis of precise energy sums alone. studie vicini these ions v putt comple gestic isoto; are a] gatior While ly, hc theore conv1c and tr refine on the ation. 292 Comparisons with previous conversion—electron and reaction studies on each isotope are made. Shell—model level spacings in the vicinity of Pb203’20l+ and the various theoretical calculations on these isotopes are discussed. Some perfunctory comments and suggest- ions were made concerning possible shell—, collective, and quasi— particle configurations of a few selected excited states. It seems rather unbelievable that this thesis is nearly completed, but before concluding I feel compelled to make a few sug- gestions concerning the direction of future investigations of these isotopes. 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APPENDICES Z<~uk~umk 299fl APPENDIX A TAKE CARE FORTRAN Listin anmsm.mumsmHsmH~mHvho5 noon ox» .znn oznno on xamoonn mean no» nn .>Jno(n o5n>n5 mxn mozn5 Panza or» no mononmzu oz» oma mmnn m1» 55a onmemxm5 no amoraz . one .mzo snzo omoo o534nmoc nmzeoz< nuana mzo omznnaon xeoo mmoo Hum“ mnmy n: 024 coma m1» non >my m.“ oz< .zoaomn >mx.ooma.o or» non >my o.“ o» hum mm hoax >m1» omHnHumnm eoz mm< mmuzammno» or» no mx«mn >onmzu 1m": mxe no one or» 2o Fax“; or» we no 7onona >mx.ooma.o or» 21 mmx 2n muzMJ emu» are ozloanuznc ennzn mnm>mn zzo7x no mmmzaz . on npnzn mo5 23ozy mxn oza 5m>m5 51 m1» zomznmm muzmmmnnno or» >an»«m roars m7< epneso oz< m4<>nmezn >my a as m5m>mo >onmzm no how 7xo2y or» no zaom one; moan zonnnozou or» ozo>nmnsam w74 Paneno 014 im07m5 pan?“ m1» 554 zmmznmm mozommnnnn or» meansunau sang mx.e mno5< im.ofinac»mn ..m.mn.. m1» ozfieww».~xH~H1aveo5<.maa pznan mmzon<.xnxczon anfinnx Ma 00 msthzm mmm 0» mo 000 o» mo.o.w2.mHvu~ A. mDZHFZQU .sfiIHv»mn..x is+acmnmn Iuonon<.m>on< iixosmncoH.xsficew~xm~Hfi~>nxv hand 44 mnwn .au>m .auxm H+mxa<1nmyaunm7m or» non eommzm or» oza .nmnmmonmzm NI» mm< yomo man a mm>o mesa: Po? > eomn < m<1 024 .>ommzm meannnonnn< m1» 07¢ nnno o op a zonnc nonnon mos xi «non mxe nosn an“; on mnmnmzno .«mesnzou s- “1wH7/Hu 2H sndummxmav 4> r CALL PLBT (0'150012I10110) CALL PLBT (OOIOOIOllvolo) CALL PLBT (0011040091110110) CALL PLGT (40959110900;1l10110) CALL PLBT (4095010.:1110116) CALL PLGT (001001111011o) X300 DB 4 13118 JI‘E XIX+5000 YIlSo CALL PLBT (XIY:JI;SX;SY) JI'l YI'lSo CALL PLGT (XIYIJIISXISY) CENTINUE CALL PLST (4095010012110119) CALL PLOT (00:0'I111-119) CALL PLBT (00110900I1110I1') PLOT TITLE CALL PLeT (loo-1995012110110) CALL CHAR (100.1995-1IPRINT;64:0¢IO.3O) CALL PLBT (0010012110110) CALL CREAD (NINCHANINRUNINERRR) IF(NERRR9NE00) 68 T8 1313 DC 10 I-11NCHAN AN(I)-N(I)+1 B810 AUTOMATIC SCALING AND DATA PLBTTIVO Do 11 I-liNCHAN IF(AN(I)OGTOB)BIAN(I) EN'bo IF(BOLEOIOOOOOO)EN'50 IF(BOLEolOOOOo)ENu40 IF(BOLE°1OOO')EN'30 lF(BoLEOlOOo)ENl2- DC 676 I'lINCHAN AN(I)=ALfiGlO(AN(I))“(7500/EN) JI=1 X'Cl DO 16 I‘lJNCHAN X3X+1o Y:AN([) CALL pLBT (XIYIJIISXISY) 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 FHW(1H 111 nrwn 666 1500 1700 1313 CBNTINUE SCALING AND PLBTTING LGG SCALE CALL NCHAR('7001001110930111000) CALL PLBT ('150I0012l1-1101 CALL PLGT ( 1501000111011.) YEOo . NENIEN DB 111 IzllNEN YI(7500/EN)&I CALL PLBT (”15llT)2)10;10) CALL PLBT ( 1501Y91110110) XI-1000 CALL NCHAR (XIYIIIOI3OIIIO'O) CALL NCHAR (-7o-IY001003011IOOO) YIY+28¢ CALL NCHAR (*AOOIYIIIO.2511;000) CONTINUE X30. LABELING PEAKS WITH FNERGIES FiEAD 1105)SSIENDUISOOIERRI1313)KIIPRINT F6RMAT(I4:16A4) XK'K IF(XK-LT0(X+25.))XK.X+25 XIXK CALL PLGT (X’7SOOI2I10110) CALL PLBT (X181001111911I) XIXK*150 cALL PLBT (X18100;211-11') CALL CHAR (X18100:IPRINTI6I9OOIOO30) GS TB 666 MARKEIMARKE+1 IF(MARKEoEQoa) Go To 1700 X89300. YI'SO. JI'E CALL PLBT (XIY1J115XISY) GB T8 999 JI'CI CALL PLOT (XIYIJIISX15Y) END "H 306 ozm om znnkmm mm inocomou . .om.~m x u x 4 am inocoznm u .H .Nm 6 > . > mm x Nm one o my .ijvznnn~».xv a<1u 44ozv n” om H. 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