GAMMA» RAY set-zomoscomc STU-DY 0F . = ' = ~ EXClTED' STATES m ‘17 Sb Thesis for the Degree of M. S. ‘ MICHIGAN STATE‘U'NIVERSITY ‘ ° ' ‘ KENNETH EUGENE SHAFER, 1A. . _ m . ‘1977. ‘ . 5 L [B R A R Y Michigan State University ABSTRACT GAMMA—RAY SPECTROSCOPIC STUDY OF EXCITED STATES IN 1178b by Kenneth Eugene Shafer, Jr. The structure of 117Sb was studied via the 117Sn (p,nY) 117Sb and 120Sn(p,llnv)ll7Sb reactions using the techniques of in-beam gamma-ray spectroscopy. Experiments which were conducted included gamma-ray singles, gamma-gamma coincidence, gamma-ray angular distribution, gamma-ray excitation function, and gamma-ray lifetime measurements. An accurate determination of gamma-ray energies and rela- tive intensities was made using the singles data and data from various standard sources. The major emphasis of this study was on the construction of the decay scheme for 117Sb. Using the gamma-gamma coincidence information many previously observed levels were identified and,in addition, seventeen new levels and thirty-five new gamma-ray transitions were added to the structure of 117Sb. Spin assignments were made to some of these levels on the basis of the angular distri- bution and excitation function measurements. As a result of the high resolution methods used the decay scheme contructed in this study showed a greater com- plexity than decay schemes from previous experimental inves- tigations. A much greater density of levels was also observed than had been predicted in recent theoretical cal- culations based on current nuclear models. Gamma-ray Spectroscopic Study of Excited States in 117Sb by Kenneth Eugene Shafer, Jr. A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Physics 1977 ACKNOWLEDGMENTS I wish to thank Dr. W. H. Kelly for suggesting this project, for his guidance during the experimental stage, and for his patience and many helpful suggestions during the preparation of this thesis. I would like to extend special thanks to Dr. R. A. Warner for his invaluable assistance with the data acquisi- tion and interpretation and in the operation of the Michigan State University sector-focused cyclotron. Special thanks also to Dr. C. B. Morgan for his guidance in the use of the various computer codes employed during the data analysis and in the interpretation of their results. Thanks also to Dr. C. L. Dors, Mr. W. Bentley, and Mr. J. Carr for their aid and advice during the data collec- tion and analysis. I wish to thank Ms. Debra Miller for the typing and preparation of the final version of this manuscript. I thank the National Science Foundation and Michigan State University for their financial support without which this study would not have been possible. TABLE OF CONTENTS LIST OF TABLES. LIST OF FIGURES . I. INTRODUCTION. II. EXPERIMENTAL. III. EXPERIMENTAL RESULTS. A. Energy and Relative Intensity Calibrations. B. Analysis of the Coincidence Data and Construc- tion of the Decay Scheme. C. Spin Assignments: Analysis of the Angular Distribution and Excitation Function Data IV. SUMMARY REFERENCES. 111 Page iv . l2 . 12 .19 . A5 - 59 . 62 Table LIST OF TABLES Detector characteristics NBS standard source gamma—ray energies and associated errors. Energies and relative intensities of gamma-rays from the decay of 117Sb. . . . . . . . . . Relative intensities of gamma—rays from 226Ra. Results of the three parameter gamma-gamma coinci- dence experiment . . . . . . . . Spin assignments for levels in 117Sb deduced from the present and several previous experimental studies. . . . . . . . . . . . . . . . Results of the angular distribution experiment in the present study. Results of angular distribution and internal conversion electron measurements made by Fromm et a1.2 Theoretical A2 values for pure M1 and E2 transitions . . . . . . . . . . iv Page .15 ,17-18 .20 .23 .5“ .56 Figure 10 ll l2 13 LIST OF FIGURES Block diagram of electronics used in the gamma- gamma coincidence experiment . . . . . . . . . Detector and target chamber arrangement in the gamma-ray angular distribution experiment. Block diagram of electronics used in the gamma- ray angular distribution experiment . . . Calibration spectra: 226Ra spectrum used to deter- mine detector efficiency at various energies. Spectrum of 11 Sb and NBS standard source gamma- rays used for energy calibration . . . . . . Sipgles spectrum of gamma-rays from the decay of Sb at an incident beam energy of 10 MeV . . . Gated spectra from the three parameter gamma-gamma coincidence experiment Decay scheme for 1178b . . . . . . . . . . . . Gated coincidence spectra after splitting the 63“. 5 .keV peak into two gates. . . . . . . . . . Gates coincidence spectra obtained after splitting the 975.9 keV peak into two gates. . . . . . . . . Gated coincidence spectra obtained after splitting the 1089.u keV peak into three gates . . . . . . . Gamma-ray angular distributions obtained from the 117Sn (p, n Y)1 Sb reaction at Ep=lOMeV . . Theoretical angular distribution curves calculated for transitions from an initial state of Ji = 7/2, Gamma—ray excitation functions. In this plot the spins of the 527.3, 1160.0, 337.0 and 1000.1 keV were taken from the work of Fromm et a1.2 and used as reference levels . Page .10 .14 .16 .24-35 -36 -39 .UI .A3 .A6-51 -53 ~58 Figure 1“ LIST OF FIGURES (cont.) Page Comparison of the level structure for 117Sb deduced in the present study to previous experi- mental level sihemes observed by Fr mm et al. , Berzins et al. , and Kernell et a1. and to theoretical leve§ schemes calculated by Vanden Berghe and Heyde and De Pinho et al.8 . . . . . . .60 vi I. INTRODUCTION One of the major goals of nuclear physics is to under- stand the systematics of nuclear structure. However, no all-encompassing theory yet exists which can correctly pre- dict the observed properties of all nuclei. Instead many different theoretical models of nuclear structure have emerged. Individually these models are usually limited in their abil- ity to produce accurate predictions and may only be useful in describing a specific nuclear property or apply to only a small region of the periodic table. The ultimate test for these theories is their ability to produce results which are in agreement with well established experimental facts. It is therefore desirable to have a large body of good experimental data available on many nuclei, especially those which are in particularly interesting regions of the periodic table. This thesis deals with a series of experiments, carried out in the M.S.U. Cyclotron Laboratory, which investigated the structure of 117Sb using the techniques of in-beam gamma-ray spectro— scopy. Many studies have been made in recent years of odd mass antimony isotopesl'6. Information concerning excited states of these nuclei are of interest because they contain one unpaired nucleon beyond the "magic number" Z=50 shell closure. 1 Several papers have been published which discuss various theor- etical approaches to the problem of predicting the properties of nuclei in this region7'9. The degree of success of each author's approach depended upon the amount of experimental in- formation which was available and which theoretical methods were chosen. In the case of the odd antimony isotopes these calculations usually involved coupling the single particle motion of the extra-core proton to various modes of collective excitation of the even-even core. A detailed discussion of such calculations has not been included in this thesis since its purpose is the presentation of further experimental infor- mation concerning the structure of 117Sb. However, some of the theoretical results have been included in a later section for comparison with results of the present and previous experi- mental work. The structure of 117Sb has been studied with a wide vari- ety of experimental techniques. Berzins et a1.1 established much of the low spin structure of 117Sb by observing the elec- tron capture decay of 117Te. Gamma-ray energies and relative intensities were determined and probable spin and parity assignments were made on the basis of log ft values. Ishimatsu et al.3 and Conjeaud et al.“ have both investigated the struc- ture of odd antimony isotopes, including 117Sb, via the (3He,d) reaction on various even tin targets. In particular, angular distributions were analyzed using DWBA methods to determine 1p values and spectroscopic factors. In each of these studies the lowest lying 5/2+,7/2+, and 11/2- states were found to be predominately single-particle in character while the lowest l/2+ and 3/2+ states exhibited a collective nature. Kernell et a1.5 studied the 117Sb(p,n)ll7Sb reaction and were able to identify eleven states in 117Sb from the neutron spectra obtained. In addition, spin assignments were made to states at excitation energies of 1.085 (37/2), 1.165 (37/2), 1.30 (37/2), and 1.355 MeV (l/2—). High angular momentum states in 117Sb have been recently studied by Fromm et a1.2 and by Gaigalas et al.6 Based for the most part on the results of 117me and 117Sn(d,2ny) experiments involving the 115In (a,2n) ll7me reactions, Fromm et a1.2 were able to establish the presence of an isomeric three-particle state at excitation energy 3.1 MeV with spin 25/2+ and Tk=3A0 microseconds. They also confirmed the sequences and spins of levels populated by the decay of this isomeric state and proved the existence of an excited 9/2+ quasirotational band. Gaigalas et a1.6 observed rotational bands in several odd antimony isotopes, including 117Sb, via the (6Li,3ny) reaction on even Cd targets. They have suggested that the band spacings for these nuclei show the characteristics of a J=9/2+ state coupled to a triax- ial rotor. In the present work the 117Sn(p,ny)ll7Sb reaction was used to investigate the levels of 1178b in a series of experiments. Gamma-ray spectra were analyzed and the results used to add to the existing level structure, to determine level sequences,.to obtain accurate gamma-ray energies and relative intensities, and to determine spins, where possible, of the various levels. II. EXPERIMENTAL 117 A series of experiments were done involving the Sn (p,ny)ll7Sb reaction. These included gamma-ray singles, gamma- gamma coincidence, gamma-ray angular distributions, and life- time measurements. In addition, an experiment was performed to obtain excitation function information which involved the 120Sn(P,Llny)ll7Sb reaction. The target used in all of the experiments, except the excitation function measurements, was a self supporting foil of 117Sn which had been isotopically enriched to 78.8%. Major contaminants in the target material were 116Sn (2.57%), 118Sn (8.03%), 119Sn (7.19%), and l208n (2.8u%). The target was made by the evaporation of first a small amount of CsI and then approximately 2.5 mg of the target material onto a glass micro— scope slide. The slide was then carefully lowered into a beaker of water which allowed the thin metal foil to float free as the CsI dissolved. An aluminum target frame was then slowly drawn up underneathtflmafloating target so that it clung to the aluminum and covered a 1/2" hole in the center of the frame. The target thickness was approximately 700 ug/cm2. In the (p,Any) excitation function experiment a 9.9 mg/cm2 target of 120 metallic Sn was used. Gamma-ray singles data were collected at incident beam energies of 6, 10 and 12.5 MeV. These data were useful for identifying gamma-rays from the decay of 117Sb and for deter- mining what beam energies would be most appropriate in succeed- ing experiments. More importantly, some of this information was used to obtain accurate energy and relative intensity calibrations. In all cases large volume Ge(Li) detectors were used. A summary of the characteristics of the detectors used in these and the following experiments can be found in Table l. The gamma—gamma coincidence experiment was of central importance to this thesis in that the information which was obtained made it possible to confidently construct the decay scheme for 117Sb. Discussion of the data analysis is left to Section B of the following chapter. The coincidence data were taken with two Ge(Li) detectors which were oriented at an angle of 90° to the beam line. A block diagram of the electronics involved is shown in Figure 1. In order for an event to be recorded a three way coincidence was required between signals from both of the gamma-ray detectors and the Time—to- Amplitude Converter (TAC). A gamma-ray detected in one of the detectors (the ORTEC 10% in this case) acted as a start signal for the TAC. A subsequent gamma-ray in the other detector (the EDAX 8%) supplied the stop signal. The ampli- tude of the TAC pulse generated was then a measure of the time between the two gamma-rays. Since only "prompt" coinci- dences were desired the TAC automatically reset if a stop signal was not received within a preset time interval. When a coincidence event occurred the two gamma-ray energy signals Table l. Detector Characteristics Resolution Detector Effi- Experimental Manufac- Type ciency Usage turer % EDAX Ge(Li) 8 singles, coinci— closed dence, angular end dist., timing, excitation func- tion ORTEC Ge(Li) 10 coincidence true coax. ORTEC Ge(Li) 18 singles true coax. ORTEC Si angular distri- surface bution barrier Ge(Li) Detector Ge(Li) Detector ORTEC 10% EDAX 8% IWJ [ml l Tennelec Amplifier fl Tennelec Amplifier ‘xr Universal Coincidence YADC Figure 1. Block diagram of electronics used in the gamma- gamma coincidence experiment. and the TAC pulse were processed through three Northern Scientific 50-MHz. ADC's interfaced to the M.S.U. cyclotron's XDS 2-7 computer, where the information was stored serially on magnetic tape. The data could then be analyzed off-line at a later time. Gamma-ray angular distributions were measured at an inci- dent beam energy of 10 MeV. The results of this experiment are presented in Section C of the next chapter and were used to verify spin assignments which had been made to various levels and to make spin assignments to levels in the decay scheme of 117 Sb which had not been previously observed. Data were taken in random order, using the EDAX 8% Ge(Li) detector, at angles of 90°, 105°, 115°, 125°, 135°, 1A5°, and 155° to the beam direction. Measurements at each angle were dupli- cated at least once during the experiment. In addition, elas- tically scattered protons were counted by a silicon surface- barrier detector which was placed at an angle of -A5° to the beam direction. A diagram of the target chamber and detector arrangement is shown in Figure 2. The elastically scattered proton counts triggered a pulse generator which then fed into the preamplifier of the Ge(Li) detector. The pulser peak was placed in a position such that it would not interfere with gamma-ray peaks in any of the spectra. A block diagram of the pulse generator is given in Figure 3. The areas of the pulser peaks could then be used for normalization of’ the gamma-ray peak areas at the various angles. The excitation function experiment was also performed with 8% Ge(Li) r-ray Detector I mil Kapion Window Figure 2. Beam Y Target Plane Silicon Surface Barrier Detector Detector and target chamber arrangement in the gamma—ray angular distribution experiment. lO Y-ray Detector Pro Ge (Li) ton Detector Si 1 1.] ~pulse out ‘\I' ,1, ext. trig. ail P1118 L — Fast 7 Timing ' Gen. Discrim. son , .rL. f '\f' , , -—trig . out Figure 3. Block diagram of electronics used in the gamma- ray angular distribution experiment. 11 the hope that the results could be used to make spin assign- ments to the levels in the 117Sb decay scheme. In this ex— periment the previously described 120Sn target was bombarded with protons at incident beam energies of 25, 30, 35, 37, 40, and A5 MeV. The resultant gamma-rays were counted using the EDAX 8% Ge(Li) detector. The lifetime measurement experiment was set-up to look for delayed transitions in the 500 nanosecond and 50 nanosec- ond regions. The cyclotron beam sweeper was first set so that only one out of eleven beam pulses reached the target. Data were taken using the computer code TOOTSIElo by dividing the time between two consecutive prompt peaks (beam on target) into ten equal sized bands. Beginning with the prompt spec- trum in the first band, each successive band contained a spectrum of increasingly delayed gamma-rays up to the next prompt spectrum. Normalization of the band width was achieved by placing a 6000 source in the target chamber with the beam off and allowing it to count into the same band structure. The total number of counts stored in each band could be used as a measure of its width relative to the other bands. The same procedure was then repeated with the beam sweeper off, i.e. looking at a time interval between consecutive beam pul- ses. The later analysis of these data, however, produced a null result. No gamma-rays were found having lifetimes in the regions which were investigated. Therefore, a further discussion of this experiment has not been presented in this thesis. III. EXPERIMENTAL RESULTS A. Energy and Relative Intensity Calibrations Singles data were taken at 6, 10 and 12.5 MeV to iden— 117 117 tify gamma-rays from the Sn(p,ny) Sb reaction. In the 6 MeV run states up to approximately 2.3 MeV of excitation were observed with states of low angular momentum being 1178b excited more prominently. Gamma-rays from the decay of were again clearly in evidence at 12.5 MeV, but transitions from higher spin states were more pronounced. Analysis of all of the spectra was accomplished using the peak-fitting computer code SAMPOl2 to determine peak areas and energies. It was decided on the basis of the spectra obtained that suc- ceeding experiments involving the (p,ny) reactions would yield the best results if run at an incident beam energy of about 10 MeV. In constructing the decay scheme of 117Sb it was impor- tant and useful to accurately determine the energies of the observed gamma-rays. An accurate energy calibration was obtained by taking an in-beam singles spectrum at a beam energy of 10 MeV while simultaneously counting gamma-rays from an NBS standard source. When plotted, the resultant spectrum clearly contained both 117Sb and NBS peaks with the most intense peaks 12 13 from each being of approximately equal size. This spectrum is shown in Figure A. The energies and the errors for gamma-rays from the NBS source are listed in Table 213-15. Using these energies and the program SAMPOlZ, a sixth order polynomial fit was made to the other peaks in the spectrum. A much lower order polynomial would have been sufficient to obtain a good fit through most of the spectrum, but using the higher order gave the best overall fit, including the relatively nonlinear low and high energy ends. Energies and uncertainties were thus determined for a large number of the 117Sb gamma-rays. However, several 117Sb gamma—rays were masked by larger, over- lapping NBS peaks. Also, many of the less intense transitions from 117Sb were not clearly in evidence (i.e. did not stand up above the background far enough or have a good enough shape to be recognized and fit within reasonable error limits by SAMPOl2). Therefore, a second energy calibration was done using singles data taken during the gamma—gamma coincidence experiment at 10 MeV (1178b only). This spectrum, shown in Figure 5, was particularly good in that even peaks from the relatively weak transitions were statistically well pronounced and were easily fit by SAMPOlZ. This time a seventh order polynomial fit was made to the data using the energies and uncertainties for the major 117Sb peaks that had been deter- mined in the previous calibrationr Again the high order poly- nomial gave the best overall fit to the data including the relatively nonlinear extremes. The final list of calculated gamma-ray energies and the associated uncertainties can be found in Table 3. 1A :- N O \O :T' (\I O O C) O O O O O H H ta Pi r% H H L r r r T D r 7 T F _—O Q i- O o ‘o :- >n1 V1.V()— (.0 8h'l'vil- g _ N “.98?- LIJSB 99t\- °° 53 90'ZZI- i70'88- Figure A. Calibration spectra: 226Ra spectrum used to deter- mine detector efficiency at various energies. Spectrum of 1178b and NBS standard source gamma- rays used for energy calibration. 15 Table 2. NBS standard source gamma-ray energies and associated errors. GggfiiEgay Ifingy (EEV) Y/S 10900 88.0u 0.01 1019 5706 122.06 0.01 1452 5700 136.u7 0.01 - 137Ce 165.85 0.01 1726 203Hg 279.19 0.01 2730 113Sn,113m1n 391.69 0.01 3uu0 85Sr 51u.00 0.02 u010 1370s,137mBa 661.64 0.02 38Ao 88y 898.02 0.02 17uu0 6OCO 1173.21 0.03 8030 5000 1332.47 0.03 80u0 88 Y 1836.01 0.04 18560 0'I9L- V'VEL-— V'6IL‘ O'OOL- 6°[L9- E°Z99" S'VE9- 11758 SINGLES AT lOMEV Figure 5. 16 10° 2000 1000 110“ 2 10 100 O'OOEZ- i J L'S8BI- * i T‘Wvfi ‘v'vv—v i 6°vaI- A €‘9ILI- -w 1 q i L'IO9I- v V-vvvw— 6'LSSI- ( 9’SESI- 4 1 W‘— 8'ILVI- 8°ESVI- HOW) 3000 CHANNEL NUMBER Singles spectrum of gamma-rays from the decay of 117Sb at an incident beam energy of 10 MeV. l7 Table 3. Energies and relative intensities of gamma—rays from the decay of 1178b. Energy 6E Relative Intensity I8886618y (keV) (keV) (Iv/1527.3) x 100% Error 163.1 0.3 1.99 0.15 221.7 0.1 0.89 0.07 289.3 0.1 1.29 0.10 337.0 0.1 2.99 0.20 366.0a 0.1 - - 374.5 0.1 12.44 0.72 382.4 0.1 1.88 0.12 432.3 0.1 0.96 0.09 446.3 0.1 2.85 0.17 527.3 0.1 100.00 5.69 632.7a 0.2 _ - 63u.6a 0.2 - _ 662.4 0.1 1.61 0.12 671.9 0.1 3.73 0.24 700.0 0.1 6.73 0.51 706.9 0.1 1.06 0.15 719.4 0.1 25.52 1.46 734.4 0.1 1.84 0.13 761.0 0.1 0.91 0.08 783.3 0.1 2.61 0.28 795.9a 0.2 _ _ 796.3a 0.2 - - 905.7 0.1 1.58 0.14 923.3 0.1 33.04 1.89 943.7 0.1 3.41 0.23 960.1 0.1 9.93 0.57 996.4 0.2 2.10- 0.19 1000.1 0.1 1.32 0.17 1008.7 0.1 4.35 0.30 1032.4 0.2 1.03 0.12 1051.6 0.2 1.45 0.23 1071.9 0.2 2.08 0.16 18 Table 3 (cont.) Energy 6E Relative Intensity Iiizfiéziy (keV) (keV) (IV/1527.3) x 100% Error 1089.4 0.2 47.59 2.74 1090.6a 0.2 - - 1099.3 0.3 1.11 0.15 1102.9 0.2 4.24 0.27 1160.0 0.1 26.70 1.56 1182.5 0.1 3.65 0.24 1215.7 0.2 2.18 0.16 1233.7 0.2 2.18 0.21 1310.6 0.1 17.75 1.03 1323.1 0.1 7.37 0.44 1353.4 0.1 5.03 0.37 1358.4 0.2 0.63 0.14 1378.9 0.1 12.71 0.73 1453.8 0.1 9.35 0.54 1471.8 0.1 8.46 0.54 1535.6 0.2 3.52 0.23 1557.9 0.2 1.23 0.12 1601.7 0.2 1.29 0.12 1630.2 0.2 2.20 0.16 1716.3 0.2 6.97 0.48 1742.9 0.2 2.81 0.18 1751.8 0.2 2.81 0.19 1761.0 0.2 0.57 0.17 1885.7 0.2 1.13 0.10 2299.3 0.2 2.47 0.19 a Relative intensities undetermined for these gamma-rays due to the overlap with a peak of nearly the same energy. 19 Table 3 also contains the intensities of the gamma—rays from 117Sb relative to the 527.3 keV transition. These inten- sities were calculated for gamma-ray peaks in the singles spectrum shown in Figure 5. Peak shapes were fit by a gaussian with exponential tails and the areas determined using SAMPOle. The intensity of each gamma-ray was then taken to be the peak area times a weighting factor which accounted for the effi— ciency of the detector at that energy. Detector efficiencies were taken from an efficiency curve for the EDAX 8% detector. The data for this curve were obtained by counting gamma-rays from a 226Ra source with the detector in the same configuration as it had been when the singles data were taken. The spectrum is shown in Figure 4. The efficiency curve was then calcu- lated and plotted by the computer program EFFl6 using the 226Ra l7 gamma-ray intensities found by Meyer et a1. These relative intensities are shown in Table 4. B. Analysis of the Coincidence Data and Construction of the Decay Scheme Much of the 117Sb decay scheme had already been established by previous experimental work. Some of these experiments and their results were briefly discussed in an earlier portion of this thesis. The main purpose of investigating the 117Sn (p,ny)ll7Sb reaction was to obtain new information concerning the structure of 117Sb to add to what had previously been found by others. The gamma-gamma coincidence data were by far the most important in this regard. A number of new levels and 20 Table 4. Relative intensities of gamma-rays from 226Ra EY 5E Relative Intensity Error (keV) (keV) Y/DPM % 53.24 0.02 0.123 7.0 186.180 0.004 0.032 242.00 0.02 0.079 3.5 258.99 0.06 0.0058 4.9 274.67 0.06 0.0050 4.4 295.241 0.202 3.6 351.96 0.02 0.401 3.6 405.7 0.1 0.0071 7.4 454.8 0.1 0.0033 7.0 461.8 0.1 0.0022 7.5 469.0 0.1 0.0013 10.5 474.5 0.1 0.00076 13.0 480.44 0.1 0.0033 7.0 487.13 0.1 0.0045 6.2 580.2 0.1 0.0036 7.0 609.27 0.05 0.484 3.3 665.40 0.07 0.0165 4.7 702.1 0.1 0.00545 8.0 719.85 0.1 0.0042 8.0 768.453 0.1 0.532 3.5 785.80 0.1 0.0121 4.6 806.16 0.1 0.0131 4.5 839.04 0.1 0.0060 5.5 934.06 0.6 0.0334 3.8. 964.12 0.1 0.00427 8.1 1051.96 0.1 0.00324 9.0 1120.28 0.06 0.160 3.3 1155.17 0.07 0.0182 4.4 1207.52 0.08 0.0048 8.0 1238.13 0.06 0.062 3.6 1280.98 0.08 0.0156 4.8 1377.64 0.05 0.0418 4.6 1385.33 0.06 0.0086 5.7 1401.44 0.06 0.0144 5.2 1407.98 0.06 0.0260 4.9 1509.22 0.07 0.0230 4.4 1583.12 0.1 0.0076 6.3 1661.24 0.07 0.0121 6.0 1729.55 0.07 0.0307 4.0 1764.49 0.07 0.166 3.3 1838.33 0.1 0.0041 5.2 1847.44 0.07 0.022 5.7 2118.52 0.1 0.0123 5.0 2204.14 0.1 0.0530 4.0 2293.21 0.1 0.0034 7.0 63 0.1 0.0165 4.1 2447. 21 gamma—ray transitions were added to the 117Sb decay scheme based on the results of the coincidence experiment. However, a problem which had occurred during the experiment made the recovery and analysis of the data somewhat difficult. The data had been stored on eight different magnetic tapes, each of which contained information from both of the Ge(Li) gamma- ray detectors and the TAC. Normally, the gamma-ray data on all of the tapes would have been added together for each of the detectors to form two integral spectra. However, this proce- dure could not be followed for the data taken by the ORTEC 10% detector, because slight gain shifts were noticed in the data between the fifth-and sixth tapes and again between the sixth and seventh tapes. These shifts were probably caused by minor equipment adjustments that had been necessary during the course of the experiment. As a result, the data from this detector had to be analyzed in three separate groups. The first five tapes were combined to form the first integral spectrum. The sixth tape was treated separately from all of the others. Finally, the seventh and eignj1tapes were added together, but could not be combined with the first five or the sixth. Gates were set for the gamma-rays in each of the three spectra and the computer program KKRECOVERYl8 run to obtain the coincidence information from data taken in the EDAX 8% detector. Fortunately the EDAX 8% detector and its associated electronics were stable throughout the experiment so that the data from this detector on all eight tapes could be added into one integral spectrum. This allowed a single coincidence 22 spectrum to be obtained for each gamma-ray of interest even though it was necessary to use three slightly different gates in the recovery process. Coincidence spectra for some of the more important gates are given in Figure 6. A complete list of the gated coinci- dence results is given in Table 5. Parentheses around a num- ber indicate a weak coincidence. In this table coincident gamma-rays with an asterisk were from contaminant nuclei. In almost all cases these coincidences were due to the presence of gamma—rays from contaminant nuclei of nearly the same ener- gy as the gated gamma-rays from 117Sb. A large portion of the decay scheme was readily constructed from the vast amount of information available in the coinci- dence data. The 117Sb level structure deduced and gamma-ray cascades observed in the present work are shown in Figure 7. Spin assignments to the various levels are discussed in the next section of this thesis. Many new levels and a number of new gamma-rays have been added to the structure that had been established by previous work (notably Berzins et al.1, Heiser et a1.19 and Fromm et a1.2)._ Levels which were added on the basis of the coincidence data are at excitation energies of 1378.9, 1471.7, 1487.4, 1535.6, 1623.3, 1630.2, 1742.9, 1751.8, 1885.7, 1974.9, 1995.2, 2022.0, 2033.7, 2039.7, 2085.2, 2129.0, and 2295.5 keV. New gamma-rays which were placed in the decay scheme had energies 221.7, 289.3, 382.4, 446.3, 552.3, 632.7, 662.4, 671.9, 700.0, 706.9, 734.4, 761.0, 796.3, 905.7, 943.7, 23 Table 5. Results of the three parameter gamma-gamma coinci- dence experiment. Gated Gamma-ray Coincident Gamma-rays (keV) (keV) 221.7 (1071.9) 1089.4 289.3 (917) 1089.4 337.0 362* (366.0) 374.5 511 527.3 1160.0 366.0 238* (270)* (273)* (337) 374.5 374.5 (114) 337 0 366 0 527.3 (761.0) 1160.0 382.4 960.1, 1089.4 446.3 1089.4 527.3 (192) 511 552.3 632.7 783.5 795.9 960.1 1008.7 1102.9 1182.5 (1215.7) 1233.7 (1353.4) (1358.4) (1557.9) (1601.7) 552.3 158.5* 527.3 960.1 634* 527.3 719.4 662.4 1089.4 671.9 (192)* (270)* 511 1089.4 700.0 270* 335* 369* 923.3 706.9 923.3 719.4 634.5 734.4 996.4 (1032.4) 1090.4 1150 734.4 719.4 761.0 197* 374 5 783.5 527.3 795’r 527.3 1089.4 905.6 719.4 923.3 242* 700.0 706.9 1051.6 1071.9 (1084) 1099.3 1160.0 943.7 (527.3) 1089.4 960.1 527.3 552.3 996.4 (527.3) 719.4 1008. 527.3 1032. (719.4) 1051.6 923.3 1071.9 923.3 1089’r 221.3 (289.3) 382.4 446.3 662.4 671.9 719.4 796.3 943.7 1099.3 527.3 (923.3) 1102.9 527.3 1160.0 (163.1) 337.0 (366.0) 374.5 1182.5 527.3 1215.7 527.3 1233.7 (220)* (252)* 527.3 1358.4 527.3 * Contaminant nuclei; llng, 1183b, 117Sn 7 Doublet 24 :2 ' 337.0 Kev GATE . 5:" . 500 r i r g T8 g 1 250 . i . 7 )- 1 ‘f 4. ‘ O 1. 289.3 KEV GATE m 85' . 88 s i A 2 g a . ( E2) l E k 44 ‘3 e 8 ' : 221.7 KEV GATE 0 . g ‘ 200 L \ 100 i “.1414 1 ‘ . ‘ 0 500 1000 1500 2000 CHANNEL HUNGER Figure 6. Gated spectra from the three parameter gamma-gamma coincidence experiment 25 O 0 O 0 0 O O O O 0 O 5 2 l 0 2 1 0 5 2 f . A 1 +1 . q . t q . pt C5 C5 T T T .h A" .n no no 00 v v V E E rE 3K eK K a. A 5 no ac uT u. 8 7 u. 3 3 .1 T o.ooHH . e.mmoH . e.mmoH . H.066 . o.Hos . v 4 v 1 m.s~m . o.oomxr Mm 0.5mm - u - «Ha . P ' 1500 42425.5 mmm WBZDOU CTUUI‘EL Blflflflflfl Figure 6 (cont.) 26 I 200 ‘ 100 ‘ 200 100 s KEV GATE r EIB‘i v.0Hh I m.hmm I T A V 552.3 KEV GATE H.ooa I m.hmm I Acmsfiac m.mmH - ' P b I GATE V 527.3 KEV Y H.0cm I .mmMH .mmmanuu .MMNH .mflmanw .mmHH - m.NoHH I h.mooH I mt‘fi V‘V o.mms.II m.mms I s.~mo I m.mmm I HHm I AMZZfimU mum mEZDOU 1500 1000 CHANNEL NUHBER Figure 6 (cont.) COUNTS PER CHANNEL 27 700.0 KEV GATE - 270 63 m I ; ° 671.3 KEV GATE - 511 *0 662.9 EV GATE “1089.; j A L 1000 1500 CHANNEL NUNBEB Figure 6 (cont.) 400 200 200 100 80 40 28 COUNTS PER CHANNEL ' 734.4 KEV GATE 1 .200 I 53 . L 4100 713.4 KEV GATE 3 0 e g i 200 i ' T T ‘ '7 § § :j 1 100 ‘ A" 706.9 REV GATE 7 0 J 1060 Eco 2030 0 CHANNEL men Figure 6 (cont.) COUNTS PER CHANNEL 29 - 527.3 - 1089.4 785.9 KEV GATE J - 527.3 733.5 IEEV GATE son 1030 761.0 KEV GATE 1 1500 CHANNEL NUNBEB Figure 6 (cont.) 200 100 . 300 ' 150 ‘ 80 40 30 0 0 O 0 0 0 0 2 l 0 l 0 8 4 d 1 1 r 1 .r T c: c; .I .I .E. An An An no. nu no my uv “V :5 e: HVB 2V“ 13"“ 7. s 7 3 3 . .uI ac “w no co co T .4 .. o.ooHH I v.0mcH I m.mmoHI m.aeoa m.amoH\\ m.oos . I c.oos e was v i 1+ m.smm I New I AHZZCEU mum mBZDOU CHANNEL NUNBEB Figure 6 (cont.) 31 0 0 0 0 0 0 m m 0 m. H 0 MW m 0 v d 1 4r 1 1 1 1 Ar 1 J 1 l m 9‘ a: :5 h T T E A A T 1. G G A v V G H m in m 11 I v r 1 K 1 m U” —/o 1 * 1 I S 8 a 8 m m .1 m I. 9 w r t 1. AM... 1m 2.. - m m.®mh I m.Hh®I f 1. TN?! .w mom-NM“- HHm I MoFNm I n.0vv v.Nmm I h.HNN I AMZdeU mum mBZDOU Figure 6 (cont.) COUNTS PER CHANNEL 32 1233.7 REV GATE r I 200 m I r‘ ‘ N Ln I 100 ; A 1182.5 Rev GATE 4' 0 P ‘ 200 100 Figure 6 (cont.) 33 mmmzaz szz> 4y> UJ Lu 54 34 U2 U2 3" 3' m ('0 co co L 1» V'6TL’ V'GIL- L 1h E'LZS- qanuvuo 83d smunoo Figure 8. Gated coincidence spectra after splitting the 63u.5 keV peak into two gates. 2000 3000 “000 CHANNEL NUMBER 1000 NO the 527.3 and the 1089.” keV gamma-rays. Simply placing the 1089.“ keV gamma-ray in a cascade to the 1323.1 keV level was not plausible since it was not in coincidence with either the 527.3 or the 1323.1 keV gamma-rays. Therefore, it was hoped that clear evidence could be obtained to indicate that two gamma-rays with energies around 795.9 keV were being seen. The 795.9 keV peak was divided into two approximately equal sized gates. The resulting coincidence spectra are shown in Figure 9. The 527.3 and 1089.“ keV peaks showed up in both gates, but there was a marked decrease in the intensity of the 527.3 keV peak from gate #1 to gate #2 while the 1089.4 keV peak remained relatively constant in intensity. If both were in coincidence with the same gamma-ray their intensities would be expected to vary in the same way. Also, the centroid of the 795.9 keV peak in the 527.3 keV gate was in channel l3lh.8 while in the 1089.4 keV gate it occurred in channel 1316.5. This corresponds to a difference in energy of about 1.0 keV. The shift of nearly two channels was considered to be significant since calculations of the centroids of other gamma—ray peaks which appeared in more than one coincidence gate showed variations of no more than a few tenths of a chan— nel from one gate to another. The conclusion drawn was that the 1089.4 keV peak in the 795.9 keV gate was actually due to a coincidence with a second gamma—ray with an energy of about 796 keV. The placement of this gamma-ray in the decay scheme could not be determined though, until the coincidence infor- mation in the 1089.h keV gate had also been sorted out. ul O O O O O O N H 0 CD :r O L 4L E; :- N .— .. -r U] UJ I— I— < < (9 CD O *> 4r> 3 uJ uJ In bfi Sfi 02 02 U) U) 0) O) |\ l\ c. In (D x. :I 2. L .. “NJ $9 2. V680? 9'6801- E L) . + 8 0 CI. E'LZS' g‘ng- TSNNVHD 33d SLNDOD Figure 9. Gates coincidence spectra obtained after splitting the 975.9 keV peak into two gates. ”2 The analysis of the 1089.” keV gate was expected to be difficult at the outset because Berzins et al.1 and Heiser et al.19 had each reported a gamma-ray of about this energy in completely different parts of the 117Sb decay scheme. The 1 had an energy of 1090.8 keV gamma-ray seen by Berzins et al. and came from the decay of the 1810.6 keV state into the 719.8 keV state. On the other hand, the 1090.0 keV gamma-ray found by Heiser et a1.19 came from the decay of the 252”.5 keV state into the 153”.5 keV state and although it was relatively weak, it was thought to be an appreicable fraction of the total observed 1089.” keV peak. It was also known that there was a gamma-ray of energy 1091.8 keV in the decay of 118Sn. Since 118Sn was one of the major contaminants in the target material the possible interference of this gamma-ray could not be ig- nored. In view of what was anticipated, the actual results obtained in the 1089.” keV gate were rather surprising. Several coincident gamma-rays were found, but, with the exception of the 719.” keV peak, none of them had been reported by any of the experimenters mentioned earlier. In fact, due to a lack of expected coincidences, the gamma-ray seen by Heiser et al.19 and the one from the decay of 118Sn seemed to not be present at all. A more careful analysis was made using the same tech- nique as before, only this time the peak was divided into three coincidence gates. The results obtained with the first two gates are shown in Figure 10. The third gate was set at the high energy edge of the 1089.” keV peak to see if any of the coincident gamma-rays could be attributed to 118Sn, but no ”3 (I) :3- oo :1- :1' N 0 CD 3‘ O T V i T Y—7 ’Y o I- ' 8 :- N o-n * . uJ Lu !— t- < < (9 (D O > db> 4 Tu Lu- 3 3‘ 5‘ 3: 32 a) O) m (D Q C) ,_. o-Q an x: :3 z: D b 1» «Is—l N‘fi z: E L'svs- L'EV6- €‘96L- €'96L‘ V'6IL- 6'IL9- 6'IL9- Q ‘~ v°299 *:3 CI! 2'9vv- 8'97?- v'zec— P°88€' c'eaz- E'693' L'IZZ- L'Izz- TQNNVHD 83d smunoo Figure 10. Gated coincidence spectra obtained after splitting the 1089.” keV peak into three gates. ”” prominent peaks were seen. Gate #1 contained strong coinci- dences with gamma-rays at energies 221.7, 382.”, ””6.3, 662.”, 671.9, 796.3, and 9”3.7 keV, but the 719.” keV peak was notice- ably absent. In gate #2 the 719.” keV peak did appear along with the gamma-rays that were in the first gate, however, the latter were greatly reduced in intensity. The centroids of the 1089.” keV peaks in the 671.9 and 795.9 keV gates were calculated and found to agree within about two tenths of a channel (channels 1802.2 and 1802.” respectively), while the centroid of the 1089.” keV peak in the 719.” keV gate was cal- culated to be in channel 1803.9, representing a shift in energy of about 1.0 keV. Also taken into consideration were the observations that the relative intensity of the 1089.” keV peak in the singles and integral spectra was quite large and that all energy calculations had yielded an energy only slight— ly larger than 1089 keV for this peak. On the basis of these results a 1090.” keV gamma-ray was placed in the decay scheme which cascaded into the level at 719.” keV and a new level was added at 1089.” keV that decayed directly to the ground state and into which all of the coincident gamma-rays in the 1089.” KEV GATE #1 cascaded. C. Spin Assignments: Analysis of the Angular Distribution and Excitation Function Data Tentative spin assignments were made to many of the levels in the 1178b decay scheme (Figure 7) based on the results of the gamma-ray angular distributions taken at an incident beam energy of 10 MeV. Peak intensities in the angu- lar distribution spectra were obtained from the peak-fitting computer code SAMP012. The normalized intensities for each gamma-ray were then fit to the equation, 'W(0)=AO 1+A2*P2(cos 0)+A4*Pu(cos 0) using the least square fitting computer code GADFIT2O. The angular distributions which were obtained are shown in Figure 11. The solid line represents the least squares fit to W(0) from GADFIT20. The gamma-ray energies and the extracted A2 and A“ values are given with each plot. The associated errors for the A2's and Au's are the numbers in parentheses in the figure. In assigning spins to the various levels in 117Sb exten- sive use was made of the tables of angular distribution coeffi- cients compiled by Der Mateosian and Sunyarzl. A short compu- ter program was written which used their tabulated values to calculate and plot theoretical angular distribution curves according to the formula, ”5 ”6 1.6 I.“ q 102-1 I " 10 I— ' 4 .. I I a i L“ 08-1 1 .— 2 H 06-- .‘I .. BY=337.0 keV lay-446.3 keV Az=-0.037 (0.049) Az-0.046 (0.042) .21 A4=0.075 (0.080) A4-0.148 (0.077) .0 1.61 10“ A 1.2.. 53' z 5 .84 i I .— 2 H .61 .‘+ . lay-289.3 keV ray-374.5 keV A2=0.264 (0.068) A2=0.103 (0.038) .2. A4=0.259 (0.053) 714:0.160 (0.057) ,0 . . . g . : 1 . . i . . 90° 120° 150° 90° 120° 1 0° ANGLE ANGLE 5 Figure 11. Gamma-ray angular distributions obtained from the 117Sn (p, n y)117Sb reaction at Ep=lOMeV. INTENSITY INTENSITY ”7 1.6 - 13 .1 1.2 .1 1.0 .1 .8 .. .6 .1 .‘+ .1 .2 .. 0 EY=67]'9 keV A2=-0.429 (0.032) A4=0.186 (0.061) VEY=719.4 keV A2=-0.001 (0.035) A4=0.103 (0.054) 1.6 d 1.9 .. 1.2.. 1.0 q .8 1 .6 . .11 .. .2. EY=527.3 keV A2=-O.Z4S (0.024) A4=0.081 (0.036) A 4 L EY=700°0 keV A2=- A4=- 0.119 (0.072) 0.023 (0.103) 96° 150° ANGLE 1§ia° Figure 11 (cont.) INTENSITY INTENSITY ”8 1.6.4 1.”. 1.2. 1.0. 08‘ 06-1 .11., Ey=783.5 keV .EY=943.7 keV A2=-0.022 (0.096) A2=-O.Z77 (0.062) .2. A4=0.175 (0.158) A4=0.021 (0.087) .0 1.6. 1.”. 1.2. I 1.. I 1» « . I I .6. .14 1 Ey=734.4 keV { EY=923.3 keV A2=-0.498 (0.101) A2=-0.051 (0.039) .21 4=-0.303 (0.152) A4=0.110 (0.059) .0.L++~AL 124.21. 90° 120° 150° 0° 120° 150° ANGLE ANGLE Figure 11 (cont.) INTENSITY ”9 1.81 1.9. 1.2. loOfi .8. f ' I .6. .111 EY=1089.4 keV 'EY=1160.0 keV z=-0.386 (0.035) A2=0.189 (0.040) ,2- A4=0.065 (0.054) A4=0.051 (0.062) .0 1.6. 10%-4 102d IEY=960.1 keV EY=1102.9 keV A2=-0.512 (0.048) A2=0.225 (0.067) .2- A4"0-139 (0-070) A4=0.172 (0.100) 434‘ :4‘: :‘La-#': 90° 120° 150° 90° 120° 150° ANGLE ANGLE Figure 11 (cont.) INTENSITY INTENSITY 1.8 -( I.“ d 1.2. i i 1 1 141—1 1 i W .8_ i I .6- .q _ EY=1310.6 keV EY=1378.9 keV A2=0.200 (0.045) A2=0.074 (0.052) ,2, A4=O.068 (0.069) A4=0.120 (0.083) .0 1.6- 1.'+ - 1.2.1 i 1.0 .- 1 I i .8- .6- .‘1 — 13Y=1182.S kov IEY=1323.1 kcv A3=0.283 (0.063) A2=0.390 (0.047) ~24 .44=-0.004 (0.112) A4=().159 (0.076) .0 £ 1 # 1 5 # n 4 4 l . 90° 120° 150° 90°TT 120° 156 ANGLE ANGLE Figure 11 (cont.) INTENSITY INTENSITY 51 1.6 - 1.“! . 1.2 - 1.0 - .8- BY=1716.3 keV 2=-0.237 (0.055) A4=-0.007 (0.095) 13+ - 1.2 - 1.0 - .8 - .6- Ey=1471.8 keV A2=0.172 (0.068) A4=0.170 (0.098) J A .L 90° 120° ANGLE Figure 11 (cont.) 1sfin° 52 W(e)=1+62A§ax*P2(cos 9)+auA?ax*Pu(cos 0) where the a's are attenuation coefficients which depend on the degree of alignment of the nucleus. Curves corresponding to many possible transitions were plotted. A set of such curves is shown in Figure 12 for transitions from a spin 7/2 level. Other transitions which give nearly identical shapes have also been indicated. The spins of the various levels were then deduced by comparing the experimental gamma-ray angular distributions to the calculated curve shapes. The first step was to verify, if possible, spin assignments which had been made by previous researchers (Berzins et al.1, Fromm et al.2, and Kernell et al.5). In every case which was checked the deduced spin from the present data was in agreement with that which had been assigned by others. Once confidence in the method had been gained, the next step was to determine the probable spins of levels which had not been previously observed or to which no spin assignment had previously been made. Ten- tative spin assignments which have been made based on the pre- sent data are listed in Table 6. This table also contains spin assignments made by the above mentioned experimenters for comparison. 117 Since many of the transitions in the decay of Sb are of mixed multipolarity an effort was made to calculate mixing ratios following the methods of Der Mateosian and Sunyar2l. However, nearly all of the experimental A” values had such high errors that they were useless for any sort of calculations. 53 1 l l T l .. a .- ——-b L. _ _ c _ ,/ WO - . ‘ W(90°) _ <1 _ . e _ Ji Jf 1 Similar Trans. 4 a. 7/2 3/2 E2 J(2)J-2 __ b. 7/2 7/2 Ml J(1)J _ c. 7/2 5/2 E2 J(2)J-l d. 7/2 5/2 Ml J(l)J-1 _ e. 7/2 7/2 E2 J(2)J J J l J 1 90° 135° 180° Figure 12. Theoretical angular distribution curves calculated for transitions from an initial state of Ji = 7/2. 5” +Am\m.m\av m.mmmm +m\ma m.smmm m\m H.mmom +N\MH N\MH m\mH N\MH m.HEwH +-m\m.mxav o.oama mxm m\m o.am~a m.am~a m.m=EH +Am\m.m\fiv m\m m\m m.mHEH m\m.m\~ m\m.m\~ m\m.m\~ m.moga m\m.m\p m\m.m\~ m\m.m\~ m.ommH mxm mxm m.mmma N\A mxm m\m m.mmmH +N\HH N\HH N\HH m.:mmH m\m mxm 5.5wsa m\~.m\m m\E m\~ w.HA:H m.mm:a N\A m\m.m\~ N\E m.m~mfi 1N\H a.Mmma .I IN\HH N\HH N\HH H.mmmH m\sm +m\m m\m m\m mxm 6.0Hma m\>M +mxm mxm mxm mxm o.omHH mxux m\E mxh «\E :.mmoa +Am\m.m\av mxm m\m m.mmm +Am\m.m\fiv N\H N\H s.ma~ +N\A mocmpmmmm m\~ N\E m.umm .oc: . ox 0cm mm b :h :h Eh pH m Amwz U M < H0>0H maawcnmx Hmcfiuamm EEopm xnoz pcmmonm m .m0H63pm Hapcmefimoaxo w50H>0pQ Hmho>mm cam ucowopa map Song 0003006 pm 2H mHm>mH pom mucoenwfimmw caam .m mamas NHH 55 Some calculations were made using the A2 values alone, but the most that could be confidently determined was whether or not in a given transition there was a significant degree of mix- ing. Table 7 contains the most probable multipolarities of some of the transitions in 1178b, based on the calculations which were made. Some of the results of the angular distribution and inter- nal conversion electron measurements made by Fromm et al.2 have also been given in Table 7. The experimentally deter- mined A2 values and multipolarities of the present study were quite consistent with those of Fromm et al.2 for transitions which were common to both studies. It should be noted that the difference in sign for the A2'S associated with the 337.0 keV transition is not a serious discrepancy. However, the fact that the A2's for this transition do not agree within the given experimental errors is significant and can most likely be attributed to the overlap in the present study of a 335 keV gamma-ray from the decay of 1198b with the 337.0 keV gamma-ray from the decay of 117Sb. As another check of multipolarities, each experimental A2 was compared to the theoretical A2's for pure E2 and pure Ml transitions between states with the same J1 and Jf as the experimental transition. The theoretical A2's were obtained from the tables of Der Mateosian and Sunyar21 and have been listed in Table 7. Support for some of the spin assignments made from the angular distribution results was gained from the analysis of 56 .osam> was» on wouaamEhoz + .:.o h\6 mwmhm>m cm MQHESmmw Hmpmmcsm vow cmfimompmz pom an omHHQEoo moanmp Song wouMHSonQ mosam> * Emo.o osm.on mm Ammvmpa.o m:.m m.HA:- Emo.o o:m.ou mm Ammvzpo.o HE.NH m.m~ma Ammvzma.o I 1 mm .Amszsa.o Amfivmaa.o Amzvao:.o mm Abzvomm.o Em.p H.mmma Ammvmmo.o Eom.o 1 mm Mfizwmmo.o AmmVEAo.o Amavmmfi.o mm Amzvoom.o mE.EH .m.oama mm mo.o Fom.o 1 mm AHzVSOH.o “mommo.o Amavmzm.o mm Aozvmma.o o».mm o.omaa Amo.o ozm.ou mm\H2 Ammvmmm.ou mm.~: :.mmoa :Ho.o mam.ou mm\az Aopvmfim.ou mm.m H.omm ado.o mam.o- Hz Ammvnpm.ou H:.m ~.m:m oom.o -::.ou Hz Ammavmm=.ou :m.H 5.5m» I mmm.o mmxfiz ANAVmHH.os mp.m 0.00» mm\az Ammvmmz.ou mA.m m.HAo Amo.o o:m.on Hz Afizvmmo.o +mmm.o ANHV:HN.OI H: . Azmvmzm.ou 00.00- m.»mm :Ho.o mam.o- mm Amsvmzo.o mm.m m.m:z Ammvmm.a . Hao.on oom.ou mm\H2 Mazwmm.a onbm.a AHHV50H.O mmxaz Awmvmoa.o ::.ma m.:hm mm Hm.m Amo.on omH.ou mmxaz Aazvmo.m Aoavmo.m ANHV-oo.o mm\Hz Amzvpmo.ou mm.m o.Emm mmH.on omm.o mmxaz Awwvnmm.o mm.H m.mmm Ammvma “szma .pasz .oamo .axm Amaovm< .0H52 Am<©vm< >H aaMoapmpoone N.Hw pm 850nm mUSpm pcmmonm rm .mQOHuHmcmnp mm 6cm Hz cyan mom mosam> m< Hmoapmpomna .Hw pm Esopm an moms mucoEmQSmmoa compomHo coampm>coo HammopCH cam soapsnfinpmao waswcw mo mpadmmm .mospm pcmmmpa map CH pcmefipmaxm coausnflppmac awaswcm on» no mpadmmm .5 magma 57 20 the excitation function data. Singles spectra from the 1 Sn (p,”nY)llYSb reaction were taken at incident energies of 35.2, 117Sb were 37.8, ”0.0, and ””.8 MeV. Gamma-ray peaks from identified and the relative intensities were calculated using SAMPOlz. Determining spins of the levels was to be accomplished by plotting the normalized gamma—ray relative intensities ver- sus incident beam energy. Unfortunately, at 35.2 MeV and ””.8 120Sn(p,3ny)ll8Sb and 120Sn(p,5ny)ll6Sb MeV, respectively, the reactions also had relatively high cross-sections. The diffi- culties caused by the overlap of gamma-rays from competitive reactions and other problems introduced large uncertainties in any attempts at making specific spin assignments based on these data alone. However, the probable spins for several of the states in 1178b could at least be limited to two possibili- ties. In Figure 13 gamma-ray yields versus beam energies (not including data at 35.2 MeV) have been plotted and the probable spins of the levels from which the gamma-rays decay have been indicated. The spins of the 527.3, 1160.0, 337.0, and 1000.1 keV states were known from the work of Fromm et al.2 and were plotted as reference levels. In each case the possi- ble spins which were indicated by the excitation function included the spin which had been assigned based on the gamma- ray angular distribution data. 20 ' KmOII5Q' 15 -"' / 3370 Iy2+ . 11029 7/2 9/2 / E . Km2857 '5', /1089.4 7’2 ‘5’ / H5273 72* . IDu- ‘ I‘Wymm W2 , E _ O -'n94 v2 05" 0.0 1 1 I ‘ 1 l l 1 l 1 35 ‘40 45 E (MeV) p Figure 13. Gamma-ray excitation functions. In this plot the spins of the 527.3, 1160.0, 337.0 and 1000.1 keV were taken from the work of Fromm et a1.2 and used as reference levels. IV. Summary This thesis has presented the results of an experimental investigation of excited states in the 117Sb nucleus. The results were obtained from the analysis of the data gathered in a series of experiments which were carried out at the M.S.U. Cyclotron Laboratory. Most of the experiments involved the detection of gamma-rays from the 117Sn(p,ny)ll7Sb reaction. Included in this group were gamma-ray singles, gamma-gamma coincidence, gamma-ray angular distribution, and lifetime measurements. In addition, excitation function measurements were made using the 120Sn(p,”ny)ll7Sb reaction. The order- ing of excited states and gamma-ray cascades were deduced and spin assignments were made, if possible, to some of the levels. A fair amount of new information was gained in this study regarding the structure of 117Sb below 2.5 MeV of excitation. Figure 1” illustrates this by comparing the levels observed in the present work to those found by several previous experi- 1,2,5 8,9. menters and to levels predicted in recent theoretical studies Probably the most interesting feature of this comparison was that, beyond the first few levels, the complex- ity of the level structure observed in the present work was much greater than had been found in any of the earlier studies. A number of new states with spins of 5/2, 7/2, and 9/2 were 59 6O —-——— 3/20 1’2. —_ III — —— I”). 7/3‘ — 9]} —_— ’/’. —_ 7N _ —3/:’ 1/2‘ ”2 (MIA/2). 2 .04 —— W — _(5/2,7/2)0 =|1I2 _——1)/:o -—_V2 —_ —‘l/2,3/2)0 a“ __.,.. — . — — > "3',” (1/2.1/21. 0 ———11/2 2 —”"”’ v 1’2 ”I > — I’ll/22 —_)}/20 I,” — b ' m “ — — — I c _ —_ 5’20 —— 1’2 7/2 — w _ U2. ‘1’: -——_11/2- ——11/3' 0 _1/’Q : ’/3 _ 9/2‘ —_ 31/2 —_ ’/ U x ———7n —————3 v: m 3/1 1.0-5 [/3 —(1/2.1/2)4 —— —— 1/2 — 7”. —_ 7,2. _ 7/2 054 ’—-—- 0.0 a y ' a . . '!00001 "on. Iculn Kernell Voodoo In“. 00 Pin» Study Figure 1”. Comparison of the level structure for 7Sb deduced in the present study to previous experi- mental level sihemes observed by Fr mm et al.2, and Kernell et al. theoretical level schemes calculated by Vanden and De Pinho et al.8. Berzins et al. , Berghe and Heyde9 and to 61 detected and placed in the decay scheme. The proper place- ment of a large number of excited states and gamma-rays into the 117Sb level scheme was made possible by the fast, high resolution data taking and data analysis techniques which were employed, especially in the coincidence and energy calibration runs. It is of interest to note that similar results have been obtained for several other antimony isotopes which have been studied recently at M.S.U.22’23’2u. In the pasg attempts have been made to understand the structure of 1173b and other nuclei near the Z=50 closed shell in terms of current nuclear models. The success of any parti- cular theoretical treatment lay in its ability to accurately reproduce experimentally established levels. However, as decay schemes become more complex it may become very difficult to formulate reliable theoretical descriptions. Clearly there is still a great deal of information to be gained from further experimental study and it is hoped that eventually all of the details of nuclear structure may be understood theoretically. For 117Sb in particular it would be useful to extend the present studies to higher excitation energies and higher angu- lar moments by conducting coincidence and angular distribution experiments using the 120Sn(p,”ny)ll7Sb reaction. It would also be useful to make careful internal conversion electron measurements using the on—line electron spectrometer11 which has been developed at M.S.U. recently,to determine conversion l coefficients and from them multipolarities of transitions in 1178b. REFERENCES 10. 11. 12. 13. 1”. REFERENCES G. Berzins, W. H. Kelly, G. Graefe and W. B. Walters. Nuclear Physics A10”, 2”l-262 (1967). W. D. Fromm, H. F. Brinckmann, F. Donau, C. Heiser, F. R. May, V. V. Pashkevich and H. Rotter. Nuclear Physics A2”3, 9-28 (1975). T. Ishimatsu, K. Yagi, H. Ohmura, Y. 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