I LII-”.22.";- Nuclear Spectroscopic Studies of Some Short-Lived and Neutron Defic t Ien o Ga and Zn Isotopes GREGG CARL GIESLER ABSTRACT NUCLEAR SPECTROSCOPIC STUDIES OF SOME SHORT-LIVED AND NEUTRON DEFICIENT Ga AND Zn ISOTOPES By Gregg Carl Giesler The decay schemes of 63Zn, 62Zn and 6303 were investigated by high-resolution Y-ray spectroscopy in an effort to further elucidate their nuclear properties. Also, a search for B-delayed a emission from the light Ga isotopes was conducted. Such y-ray spectroscopic techniques as Ge(Li) singles, Ge(Li)- Ge(Li) megachannel coincidence, Ge(Li)—NaI(T1) coincidence, and Ge(Li)- time coincidence techniques have been utilized to study these isotopes. A He-jet thermalizer was utilized in the search for B-delayed a emission. Several programs written for data analysis are presented. Forty-five y rays have been assigned to the decay of 38.4- minute 63Zn and have been incorporated into a decay scheme containing 24 levels with energies of 0, 669.71, 962.14, 1327.0, 1412.07, 1546.8, 1860.9, 1865.7, 2012.0, 2062.3, 2081.4, 2093.5, 2336.8, 2497.5, 2512.5, 2536.2, 2697.0, 2717.2, 2780.1, 2857.8, 2889.5, 3044.0, and 3100.3 keV. A search for y rays with energies above 700 keV from the decay of 9.3— hour 62Zn was conducted and six were found at energies of 881.4, 915.6, 1142.5, 1280.8, 1389.1, and 1429.9 keV. They were placed in a decay scheme containing seventeen Y-rays and ten levels with energies of 0, 40.94, 243.44, 287.98, 548.41, 637.53, 915.6, 1142.5, 1280.8, and 1429.9 keV. The decay of 32.4-second 630a has sixteen y rays which were placed in a decay scheme containing nine levels with energies of 0, 193.0, 248.0, 627.1, 637.0, 650.1, 1065.2, 1395.4, and 1691.7 keV. Spin and parity assignments for the nuclear states investi- gated are based on log ft values, relative y-ray intensities to states of known spin and parity and charged particle scattering results. A survey of and comparison with previously reported Ge(Li) detector results and with charged particle scattering results is presented for these isotopes. The structures of the low-lying states in these nuclei are discussed and compared with theoretical calculations and systematics of the region. A search for B-delayed a emission from the short-lived (<5 sec) Ga isotopes through 600a was conducted. The y-ray and a— particle spectra from the nuclei produced are presented. An upper limit of ten parts per million was placed on B-delayed a branching from the decay of these nuclei. NUCLEAR SPECTROSCOPIC STUDIES OF SOME SHORT-LIVED AND NEUTRON DEFICIENT Ga AND Zn ISOTOPES By Gregg Carl Giesler A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry Program in Chemical Physics 1971 ACKNOWLEDGEMENTS I sincerely wish to thank Dr. Wm. C. McHarris for suggesting this region of study. His guidance, encouragement, and patience during the experimental work and preparation of this thesis are greatly appreciated. I also wish to thank Dr. w. H. Kelly of the Physics Department for his help and advice. His suggestions and advice during this project were very useful. Dr. H. G. Blosser, Mr. H. Hilbert, and Dr. w. P. Johnson assisted with the operation of the Michigan State University Sector- Focused Cyclotron, which was used to prepare the radioactive sources used for this investigation. Dr. D. B. Beery, Mr. J. Black, Mr. w. B. Chaffee, Dr. J. B. Cross, Dr. R. E. Doebler, Dr. R. E. Eppley, Mr. R. B. Firestone, Dr. R. Goles, Mr. C. Morgan, and Mr. R. Todd all deserve special mention for their assistance and advice throughout the course of these experiments. I particularly wish to thank Mr. K. L. Kosanke for his assistance with and the development of the He-jet thermalizer and pneumatic rabbit systems. Mr. R. Au, Mr. and Mrs. w. Merritt, and the cyclotron computer staff have aided greatly in the data aquisition and evaluation through the use of the XDS Sigma 7 computer. Their assistance in programming of the computer is greatly appreciated. Help has also been received from Mr. R. N. Mercer and his staff ii in the cyclotron machine shop, and from Mr. W. Harder and the cyclotron electronics shop. The cyclotron drafting staff, especially Mr. A. Daudi, have been very helpful and quick in preparing the drawings for this thesis. Our secretaries Mrs. P. Warstler and Mrs. M. Fedewa have helped in typing this thesis. Mr. J. J. Chavda prepared the artwork for the cover. I wish to thank the U. 8. Army for allowing me to continue my education and obtain this degree. I thank the National Science Foundation, U. S. Atomic Energy Comission, and Michigan State University for their financial support without which this study would not be possible. Finally, I wish to thank my wife, Maryjane, for her encourage- ment, inspiration, perspiration, and patience during the course of this study. iii TABLE OF CONTENTS ACKNOWLEDGMENTS LIST OF TABLES . . . . . . LIST OF FIGURES . Chapter I. INTRODUCTION II. EXPERIMENTAL APPARATUS AND TECHNIQUES . 2.1. y-Ray Spectrometers . , 2.1.1. Ge(Li) Singles Spectrometers 2.1.2. Coincidence Spectrometers . 2.1.2.A. Ge(Li)-NaI(Tl) Split Annulus Spectrometer 2.1.2.3. Ge(Li)-Ge(Li) Megachannel Spectrometer 2.1.2.C. Ge(Li)-Time Spectrometer 2.1.3. Ge(Li) Detector Efficiency Curves . 2.2. B-Delayed u-Emission Spectrometer . . . . . 2.2.1. a-Particle Spectrometer . . 2.2.2. He-Jet Thermalizer . 2.3. Cu-Zn Chemical Separation . . III. DATA ANALYSIS . . . . . . . . . . . . . . . . . . 3.1. EVENT RECOVERY Program . . . . . . . . . 3.2. y-Ray Energy and Intensity Determination 3.2.1. MOIRAE Spectrum Analysis Routine 3.2.2. SAMPO Spectrum Analysis Routine . . iv Page ii viii ix 10 12 l4 17 22 25 27 27 30 . 31 32 . 33 35 40 Chapter Page 3.2.3. y-Ray Energy and Intensity Calculation . 43 3.3. Decay Scheme Construction . . . . . . . . . . . 44 IV. EXTENSIONS 0F Ge(Li)-Ge(Li) MEGACHANNEL COINCIDENCE SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . 47 4.1. Compton Scattering Problems In Ge(Li)-Ge(Li) Coincidence Gamma-Ray Spectrometers (Gi7l) . . . 48 4.1.1. Experimental Apparatus . . . . . . . . . 49 4.1.2. qun Results: A Complex Spectrum . . . . 50 4.1.3. Angular Dependence . . . . . . . . . . . 54 4.1.4. Cate Widths . . . . . . . . . . . . . . 57 4.1.5. Gate Positions . . . . . . . . . . . . . 62 4.1.6. Conclusions - . . . . . . . . . . . . . 64 4.2. Ge(Li)-Ge(Li) Sum Coincidence Spectrometer (Gi7la) . . . . . . . . . . . . . . . . . . . . 65 4.2.1. Experimental Methods . . . . . . . . . . 69 4.2.2. Analysis of a Moderately Simple Spectrum: 6~"zna..................70 4.2.3. Analysis of a Complex Spectrum: 2058i (in conjunction with K.Kosanke) . . . . . . 77 4.2.4. Conclusion . . . . . . . . . . . . . . . 85 v. DECAY 0F 632a . . . . . . . . . . . . . . . . . . . . 87 5.1. Introduction . . . - . . - . . . . . - - . - - - 87 5.2. Source Preparation - . . - . . . . - . . . . - - 89 5.3. Experimental Results - - - . - - . - . - - . - . 89 5.3.1. y-Ray Singles Results - - - . - - - - - 89 l) Chapter Page 5.3.2. Ge(Li)-Ge(Li) Megachannel Coincidence Results . . . . . . . . . . . . . . . . 94 5.3.3. Anticoincidence Results . . . . . . . . 98 5.3.4. 511—511—keV-Y Triple Coincidence Results 99 5.4. Decay Scheme . . . . . . . . . . . . . . . . . . 101 5.5. Spin and Parity Assignments . . . . . . . . . . 104 5.6. Systematics . . . . . . . . . . . . . . . . . . 110 VI. DECAY 0F 62Zn . . . . . . . . . . . . . . . . . . . . 117 6.1. Introduction . . . . . . . . . . . . . . . . . . 117 6.2. Source Preparation . . . . . . . . . . . . . . . 119 6.3. y—Ray Spectra . . . . . . . . . . . . . . . . . 120 6.4. Discussion . . . . . . . . . . . . . . . . . . . 126 VII. DECAY 0F mCa . . . . . . . . . . . . . . . . . . . . 131 7.1. Introduction . . . . . . . . . . . . . . . . . . 131 7.2. Experimental Procedure . . . . . . . . . . . . . 131 7.3. Experimental Results - . . . . . . . . . . . . . 134 7.4. Decay Scheme . . . . . . . . . . . . . . . . . . 136 7.5. Spin and Parity Assignments . . . . . . . . . . 139 7.6. Discussion . 141 VIII. 620a AND B-DELAYED a EMISSION - - - . . - - - - - - - 141 8.1. Introduction - - --- - - - - - - ° - - - - - - - 145 8.2. Experimental Procedure . . . . . . . . . . . . . 148 8.3. Results . . . . . . . . . . . . . . . . . . . . 149 IX. CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . 158 BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . 160 vi APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 A. EVENT RECOVERY FORTRAN and SYMBOL Listing . . . . . . . 166 B. MOIRAE E(I) FORTRAN Listing . . . . . . . . . . . . . . 179 vii Table 10. 11. LIST OF TABLES Ge(Li) Detector Characteristics . . . . . . . . . . Characteristics of Some ADC's . . . . . . . . . Y-Ray Relative Intensity Standards 137Cs Coincidence Counting Rates as a Function of Detector Angle and Absorber Usage . . . . Energies and Relative y—Ray Intensities from the Decay of 632m . . . . . . . . . . . . . . . . . . . . . Intensities of 632m y—Rays in Coincidence Experiments . Comparison of Experimental and Theoretical 8+ Feedings for 63Zn . . . . . . . . . . . . Energies and Intensities of y—Rays Following the Decay of 622m . . . . . . . . . States Produced by Some Low-Lying Configurations in Odd-Odd 62Cu . . . . . . . . . . . . . . Measured y-Ray Energies . . . . . . . . . . . . . . . y-Ray Energies and Relative Intensities from the Decay of63Ga....................... viii Page 11 23 56 91 97 103 124 129 135 137 Figure 10. 11. 12. LIST OF FIGURES Page Portion of the Chart of the Nuclides, including the copper- zinc-gallium region of interest in this thesis. Taken from the Chart of the Nuclides compiled by the Knolls Atomic Power Laboratory, Tenth Edition . . . . . . . . . . . . . . . . . . 3 Experimental setup for recording anti— and 511-511—Y coinci- dence spectra. For a 511-511-Y coincidence spectrum the TSCA's are adjusted such that the window falls on the Sll—keV region and the linear gate is in normal mode. For an anti- coincidence spectrum the TSCA's are wide open and the linear gate is in the "anti" mode. . . . . . . . . . . . . . . . . . 13 Block diagram of the megachannel two-dimensional y-y coinci- dence system. . . . . . . . . . . . . . . . . . . . . . . . . 16 Block diagram of the y-time coincidence system. . . . . . . . 19 Display produced by TOOTSIE in Setup mode . . . . . . . . . . 21 Display produced by TOOTSIE in Run mode . . . . . . . . . . . 21 Relative photopeak efficiency curve for the 10.4% efficient detector with the sources placed 10 inches in front of the detector. . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Recoil thermalizer showing target holder—collector and Faraday cup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Recoil counting chamber showing capillary and detector in cooled mount. . . . . . . . . . . . . . . . . . . . . . . . . 29 Flow diagram of EVENT RECOVERY program. . . . . . . . . . . . 34 MOIRAE display oscilloscope and sense switches. . . . . . . . 36 Closeup of MOIRAE sense switches. . . . . . . . . . . . . . . 36 ix Figure 13. 14. 15. l6. 17. 18. 19. 20. Page MOIRAE oscilloscope display of a portion of the 632m y—ray spectrum with a seventh order background fit. . . . . . . . . 37 Display of peaks after calculated seventh order background has been subtracted . . . . . . . . . . . . . . . . . . . . . 37 Photograph of line printer output of spectrum analysis routine SAMPO showing its fit of the 1389-1392-keV doublet from m2n decay. Lines have been drawn to show the doublet and its individual components . . . . . . . . . . . . . . . . . . . . 42 Relative positioning of the Ge(Li) detectors for the Compton scattering coincidence experiments. . . . . . . . . . . . . . 51 Coincidence spectra for 63Zn. The integral coincidence spectra are shown in A and D. Gates were set on the spectrum in D as indicated by the bars, with E and F, same as B and C except that the background indicated by bar H has been subtracted. Spectrum 0 was produced by gating on the spurious "220-keV" peak. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 137Cs Compton—scattering coincidence spectra showing the effects of the angle between detectors. . . . . . . . . . . . 55 137Cs Compton-scattering coincidence spectra showing the effects of placing an absorber between the detectors. The spectra on the left were taken without an absorber; those on the right, with a 1.27-cm thick graded Pb absorber placed as shown in Fig. 16. . . . . . . . . . . . . . . . . . . . . . . 58 137Cs Compton-scattering coincidence spectra showing the effects of varying gate width. The two integral coincidence spectra are shown at the top in A and F, and the gate widths are indicated in F. . . . . . . . . . . . . . . . . . . . . . 59 Figure 21. 22. 23. 24. 25. 26. 27. 28. Page Plot of display peak widths for 137Cs as a function of the gate widths shown in Fig. 20. . . . . . . . . . . . . . . . . 61 137Cs Compton-scattering coincidence spectra showing the effects of gating at different positions. The display integral coincidence spectrum is shown in A, while the gate integral coincidence spectrum is shown in F. The other spectra corre- spond to their respective gates as indicated in P . . . . . . 63 Block diagram of the sum-coincidence experiment. The addition of the "summing network" is the only way in which this differs from a standard two-dimensional megachannel coincidence experiment, and the "summing network" is merely an addition to the offline computer recovery program. . . . . . . . . . . 71 Coincidence spectra for 63Zn. The integral or "any" coincidence spectra are shown at the top and lower spectra are gated slices 72 Total sum—coincidence spectrum for 63Zn. This spectrum was obtained by summing the addresses of each coincidence event in the integral coincidence spectra of Fig. 24 . . . . . . . . . 74 Sum-coincidence spectra for 63Zn. All of the spectra shown were taken with the limitation Y>X, and the X—axis spectra are displayed on the left opposite their corresponding Y—axis spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Sum—coincidence spectra for 63Zn with the sum gate set on the 1412.1-keV sum peak . . . . . . . . . . . . . . . . . . . 78 20531 singles y-ray spectrum taken with a 7 cc Ge(Li) detector. . . . . . . . . . . . . . . . . . . . . . . . . . . 79 xi Figure Page 29. A small portion of the 205B1 decay scheme showing those states and transitions of interest to the present discussion. The three components of the z1002-keV triplet are drawn as larger arrows to aid the eye in locating them. . . . . . . . . . . . 80 30. Total or "any" sum-coincidence spectrum for 205Bi . . . . . . 82 31. Sum-coincidence spectra for 205Bi showing the results of gating on the 1264-, 1705-, and 1764—keV sum peaks. These are all Y—axis spectra. The small arrows show where the condition YX begins. . . . . . . . . . . . . . . . . . . . . 83 32. A summary of various reactions used to study excited states in 63Cu 88 33. 63Zn y-ray spectrum. The insets show the regions at 1392 keV and 1865 keV in more detail . . . . . . . . . . . . . . . . . 90 34. 63Zn y-Y megachannel coincidence spectra. In the top of this Figure and of Part 2 are shown the integral coincidence spectra, and in the lower portions are shown the various selected gates 95 35. An anticoincidence spectrum from the decay of 632m. . . . . . 100 36. A 511-511-y triple coincidence Spectrum obtained using the NaI(T1) annulus and the 2.5% efficient Ge(Li) detector. . . . 102 37. Proposed decay scheme for 63Zn. . . . . . . . . . . . . . . . 105 38. Results of calculations of excited states in 63Cu . . . . . . 112 39. Systematics of the odd mass Cu isotopes. The results shown are from ND . . . . . . . . . . . . . . . . . . . . . . . . . 115 40. A typical y—ray spectrum of 62Zn taken without absorbers. The insets show the regions at 245 keV and 511 keV in greater detail. . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 xii Figure 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. A diagram of the sample and absorber placement used to study 622n decay. . . . . . . . . . . . . . . . . . . . . . . . . . A typical 6-h y-ray spectrum of 622m decay taken using the absorbers as shown in Figure 41 . 622m decay scheme . Systematics of N=33 nuclei. The data is from 59Fe (K167), 61N1 (c668), and 63Zn (B166). Systematics of the even mass Cu isotopes. The references are 58Cu (C067), 60Cu (Yo68), 69Cu (Da70), 61+Cu (Ba70), 66Cu (Da69) and 68Cu (Br60) . . A summary of the various reactions used to study the excited states in 63Zn. Relative production of 636a to 6”Ca as a function of incident beam energy . . . . . . . . . . . . . . . . . . . A typical y-ray spectrum from the decay of 636a . Proposed decay scheme of 63Ga . Systematics of the odd mass Zn isotopes. The 63Zn results are from the present work, 6lZn from ND, and rest from V067 . Proton and a binding energies for light Zn isotopes. Those labeled (a) are from My65 and those labeled (b) are from ND. Also included are the y-ray results from Chapter 7 An a spectrum from the B—delayed a amission of 20Na (P067). A search for B-delayed a emission in light Ga isotopes. y-ray spectrum from the recoils produced from bombarding Cu with 40 MeV T y-ray spectrum from the recoils produced from bombarding Cu with 55 MeV T xiii Page 122 123 125 128 130 132 133 136 139 143 146 148 150 151 152 Figure 56. 57. 58. y-ray spectrum from the recoils produced by bombarding Cu with 70 MeV T . . . . . . . . . . . The 63Cu(I,xn) cross sections calculated by the program CS8N. The 65Cu(T,xn) cross sections calculated by the program CSSN. xiv Page 153 155 156 Chapter I INTRODUCTION Any study of the nucleus involves the use of many models, since no one model fits more than a small number of nuclei. Although these models vary widely in their description of the nucleus, they are all semi-empirical, that is, require a number of experimentally determined parameters in order to make any predictions. Therefore, any improvement in quality or quantity of the experimental results will not only aid in improving the results obtained from the model, but also aid in the further development of the model and the description of nuclei as a whole. One of the most useful methods of obtaining information about nuclear properties is y-ray spectroscopy. With the deve10pment of Ge(Li) detectors with their present efficiency and resolution, even the very weak y rays in a complex spectrum can be seen and easily resolved from their neighbors. As a result, decay schemes previously considered relatively simple have become much more complex. y-ray Spectrosc0py, therefore, has become an important part of the study of nuclear properties. The nuclear shell model is one of the more popular models used to describe the nucleus. The nucleus, according to this model. is like an atom with the protons and neutrons individually going around in their own orbits. In addition, closed shells occur at neutron or proton "magic" numbers of 2, 8, 20, 28, 50, 82, and 126. It is found that this model only works well near these closed shells. Accordingly, most of the study of this model has occurred in the following regions: nuclei with fewer than 23 protons, those with 28 protons, 50 neutrons or protons, 82 neutrons, and nuclei in the region of the 208Pb doubly closed shell. A primary interest is in the region with fewer than 23 protons, since in this region the B stability line lies on or near N=Z. Here also there is an abundance of doubly closed shells, and each closed shell consists of at most three low spin orbits which makes the calcu- lations relatively easy. The stable isotopes of calcium which go from the doubly magic “OCa to the also doubly magic ”8Ca are found at the upper end of this region. One more doubly magic nucleus occurs near this region, r’r’Ni. It is different from the others because it is unstable to B decay and rather far from the line of B stability. The two closed shells are the lf7/2 for both protons and neutrons. In the region immediately beyond this nucleus are the 2p1/2, 2p3/2, lf5/2 and 199/2 orbits, which, even when considering only the lowest levels populated, require a complex set of calculations. Coupled with the complexity of the calculations is the small amount of information available about the isotOpes just above this doubly closed shell. The present investigation is intended to help provide information about some of the nuclei outside this doubly closed shell. In Figure l, the portion of the Chart of the Nuclides covering this region is shown. When Nurmia and Fink (Nu65) reported the discovery se . 39m 34 78.96 ear. done AS A5768) A3569 ~ m in 74.925 5‘ 9'29 '23 do“, i 5“ Ge 6666 6.6.66 366.6 8%? l m I tom 32 72.59 p‘ss.- 56:120. ”'36 23.-:1 1 . ,u_.rz $3.054. r" 1‘ H No". I c7024 :65 :50 cu c~s GO 6063'»! 60 64v 6065: Go 66¢ Go 67 V 6972 33! 26m 15 2m 95h 78 2h 31 ' no 8‘2060. n‘zunazzta‘mu ( 1 ,9928566300. 82, . c “039.) 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R ’ Java M am: v M: 339N1f_4__r_93_s_go w i133 __01_'_j»’[ __._ 0!, g“ _ I W 0.50 ' Mn 5|” 9 Mn “ Mn53' Mn54 “ Mn 55" Mn56 " Mn 57 M058 2!» case. 459m 2|4m’563d 2 . .o', 3:56 loo 582a I7m Hm I; 1'66! 31:} ,- {1.33.534 - ‘ p‘zox-m. M, v 26 .. a' ' ' "as. 4' :33: W 21‘ .. .. (7“ f3? [47- . 91h ii“, \qgggql, ‘3' 2 I." (, Portion of the Chart of the Nuclides, including the copper-zinc-gallium region of interest in this thesis. Taken from the Chart of the Nuclides compiled by the Knolls Atomic Power Laboratory, Tenth Edition. of 63Ga, they mentioned the possibility of B-delayed a emission in this region. According to the calculations of Taagepera and Nurmia (Ta6l), 636a as well as the lighter Ga isotOpes should all be B-delayed a emitters. Nurmia and Fink did not, however, report a decay scheme for the 63Ga. This region of the neutron deficient Zn and Ca isotopes holds strong promise of providing valuable information that can be used for the application of the shell model to this region. In Chapter II many of the techniques used in the course of this study of both the y-ray decay and a search for B-delayed a emission in this region are discussed. Included in this chapter is the chemical separation used in the study of the decay of the Zn isotopes. After the data are obtained, they must be analyzed to obtain the energies and relative intensities. The methods used for this analysis are described in Chapter 111. Various computer programs written for or adapted for the XDS Sigma 7 computer at the Michigan State University Cyclotron Laboratory were used to sort the megachannel coincidence data, analyze the many singles spectra, and finally calculate the parameters needed for the final decay schemes. The Ge(Li)-Ge(Li) megachannel coincidence system discussed in Chapter II has several interesting characteristics that have been studied further. These include the effects of the Compton scattering between detectors and the possibility of using the data obtained from a y-y coincidence experiment as y-sum coincidence data. A study of these characteristics and the results are discussed in Chapter IV. The results of this study of the neutron deficient Ga and Zn isotopes are described in the following chapters. Several interesting results that were obtained in the study of 63Zn comprise Chapter V. Chapter VI describes results obtained from a study of 622m in a search fory transitions above 700 keV. The decay of 33 second 636a is described in Chapter VII. Chapter VIII presents the results obtained in the search for 8 delayed a emission in the light Ga isotOpes. Finally, in Chapter IX, these results and their application to this region of light Zn and Ca isotOpes are discussed. CHAPTER II EXPERIMENTAL APPARATUS AND TECHNIQUES Each of the isotopes of Zn and Ca studied in this investigation decayed by position emission and electron capture to states in its daughter. The excited states in the daughter in general then decayed by y emission to the ground state. To study the y emission and thereby learn about the excited states, many different techniques, both standard ones and newly-developed ones, were utilized. Some of the excited states also have the possibility of decaying by a emission. In order to examine this possibility, some new techniques were utilized to collect the radioactive parent so that this B-delayed a emission could be more precisely studied. This chapter describes the techniques and appa- ratus used for the data acquisition. Section 2.1. describes the y-ray spectrometer systems used and the techniques involved in their utiliza- tion. In Section 2.2. the a spectrometer and the He jet thermalizer used to prepare the a sources and short-lived Y sources are described. Some of the experiments performed studying the decays of 622n and 63Zn required the chemical separation of the Zn from the Cu targets. This separation is described in Section 2.3. 2.1. y-Ray Spectrometers With the development of Ge(Li) detectors great interest developed in the examination of new decay schemes as well as many old ones. These decay schemes became more and more refined as Ge(Li) detectors with greater efficiencies and better resolution were developed. In the period of the four years involved in this study, the Ge(Li) y-ray spectrometers used have gone from one with a resolution of 25.6 keV FWHM for the l332-keV y of 60Co and an efficiency of <mx Nmma was com swam b m0 xmma >mx NmmH ecu cu uumammu :uHBm vaooo H cu mm >mx H.~ Nq.OH Hmwxmoo ease mmonQ ummHosz musumpmaEmu Eoou H OH qm >mx m.H No.q Hmemoo wspH omemo munumumaEmu 800» H ou mm >mx o.m No.m Hmemoo many umemo vaooo H Ou m.oH >mx N.N Nm.m Hmvwoumamuh mmwowa ummHosz eunumquEmu Eoou H cu m >mx q.m No.m Hmwwonmmmua mvaHo ummHosz musumumaEmu 800» H on m.q >mx o.m qu.o Hmwwoumamue .an coauOHozu 3m: 9mm mammum afiumm QCOHuDHommm exocmHowmmm mamfim Hmhnuummscmz acumsou ou xmwm moaumfiumuomumzu Heuomumn Aqumo .H wanes 10 may fall into the undershoot and will have an apparent area smaller than the actual area, thus causing a loss in resolution. Base—line restoration also improves resolution at higher count rates by restoring the undershoot of the amplifier signals to a DC base—line after all other shaping has been performed. This improves the resolution by reducing the pileup distortion that is produced when one pulse occurs in the undershoot of another. The DC level adjustment matches the DC level of the amplifier unipolar output to the DC level of the direct input to the ADC. This input bypasses the ADC internal base—line restorer, amplifier, and pulse amplitude discriminator stages, thus lessening the distortion of the input pulse. Also eliminated is the fixed delay (1.25 psec) added to each pulse to allow time for the dis— criminators to operate. Eliminating this delay allows a higher count rate for the same ADC dead time. In this laboratory a variety of analyzers has been used for data acquisition and represents the change in the state-of-the-art over several years. Some of their characteristics are listed in Table 2. With the interfacing of ABC's to a computer, many different modes of data acquisition not available in hardwired analyzers became available. Some of these new modes were used in this study and are discussed in later sections. 2.1.2. Coincidence Spectrometers Singles experiments are useful in determining the energies and intensities of y rays from the decay of a nucleus but tell nothing of their placements in the decay scheme. To aid in the placement of these y transitions, various coincidence experiments were performed. 11 Table 2. Characteristics of Some ADC's Maximum Number ADC of Channels Digitizing Rate Memory Nuclear Data 160 1024 4 MHz Hard wired Nuclear Data 2200 4096 16 MHz Hard wired Northern Scientific 625 dual 4096 40 MHz Interfaced to DEC PDP-9 Northern quadruple 8192 50 MHz Interfaced to Scientific 629 XDS Sigma-7 12 These include anti-(revealing direct ground state transitions), prompt- (revealing cascade transitions), delayed- (revealing transitions in cascade with states having a measureable lifetime), and 511-Sll-y (revealing double escape peaks and B+-fed levels) coincidence experi— ments. Descriptions of these techniques are given in the following sections. 2.1.2.A. Ge(Li)eNaI(Tl) Split Annulus Spectrometer One of the most useful spectrometers at MSU is the 20.3X20.3 cm NaI(Tl) split annulus. Several of its uses in conjunction with a Ge(Li) detector are described by Auble et al. (Au67). In the present study it was used as an anticoincidence spectrometer and a 511-511-Y coincidence spectrometer. Figure 2 gives a block diagram of the electronics used for these experiments. For the anticoincidence experiment, a 7.6X7.6 cm NaI(Tl) detector was placed inside one end of the annulus tunnel to increase the solid angle subtended by the annulus. A Ge(Li) detector was placed inside the other end of the annulus with the sample between these two detectors, approximately in the center of the annulus. The timing signals from the three NaI(Tl) detectors were combined in an AND/OR gate to produce a timing signal whenever a signal was produced by any of the three NaI(T1) detectors. An ORTEC universal coincidence unit with the coincidence requirement set to 1 was used for the AND/OR gate. The resolving time control on this unit therefore had no effect. The timing signal from this unit was then required to be in coincidence, within a llO-nsec resolving time, with the timing signal from the Ge(Li) 13 .0608 :Huam: onu :H mH mumw ummcflH ecu use ammo wows mum m.mxiHHm ecu do mHHmm aovcHB mnu umnu Loam vmumanvm mum m.iHHmiHHm m pom .muoomam mocmkuaHou >iHHmiHHm 6cm iHunm wdfivuooms sow aspen Hmucmeflummxm .m .mHm 004 o uhdo .280.» cuESaa‘fll 1254.3: ¢(4uo ¢>10usec. The task TOOTSIE, written by D. Bayer of the MSU Cyclotron Laboratory and described elsewhere (Ba7l), has two operational modes: Setup and Run. In Setup mode the task functions as a two-dimensional analyzer of maximum size lZBXI28 channels using the seven most significant bits of the ABC's. Bands can be drawn on this two-dimensional array, each band corresponding to a spectrum in Run mode. The maximum number of bands depends on the size of the spectra. For example, if a spectrum size of 4096 channels is chosen, five bands are the maximum number allowed. Once the bands are drawn the task can be changed to Run mode, in which each band becomes a spectrum of the designated size and the data are then taken as n one—dimensional spectra. 19 I Ge(Li) ~><~ SAMPLE I of, I 1 DETECTOR {SOURCE g h 4-—--~I I ' '7 i IJDEJU? I TIMING i AWLFIER 1 AWLIFIER [ INTEGRATOR LIMAR ‘ LII‘EAR GATE (BATE XSDE 8|92CHAM£L 8|92CHAMEL YSIDE . $ ADC ADC SYNCHRONOUS MODE I I INTERFACE TO SIGMA 7 CMTER CHANNELIK) ()UWMEL NO OF EVENT CF'EVENT FROM X SDE ”KIA Y SUE I e I TASK "TOOTSIE" ] UNDER "JANUS" MONITER Fig. 4. Block diagram of the y-time coincidence system. 20 Figure 5 shows the display produced by TOOTSIE operated in Setup mode. The display is a horizontal slice parallel to the energy- time plane, displaying all the locations having counts between the limits specified in the upper left corner. The vertical axis is the time axis and the horizontal axis is the energy axis. The numbers next to the arrows along the axis give the location of the arrows. These arrows are used to locate channel numbers and to define limits for expanding the display. This display was produced by counting a 60Co source. The solid area on the left portion of the area is the Compton tail with the two lines on the right being the two photopeaks. Discriminator cutoff in the linear gates and ADC's produces the dark areas along the left and lower sides of the display. The horizontal lines represent the lower and upper limits of five bands. The same line may be used as an upper limit of one band and the lower limit of the next band, since each band is defined as the region from the lower limit inclusive up to but not including the upper limit. These bands do not need to be of equal size and the limits can also be curves of any order polynomial up to 10. By using many bands of small size the half-life of the sample can be accurately measured, or by using a few bands of large size the determination of the parent isotope of each y ray can be made. Operational control Of the task and its display is per- formed by use of both sense switches and teletype input. In Figure 6 the display of TOOTSIE in Run mode is shown. The upper spectrum is the first band and the lower spectrum is the fifth band of the decay of 636a. Each spectrum represents a band of about 20 seconds time and has been expanded to show the region from 2550 keV to Y JII Compton Background Photopeaks Fig. 5. Display produced by TOOTSIE in Setup mode. ~.~-.,t,, »_-- ‘M/ . «Hafighn... \‘l “.1 .311 I HES! Fig. 6. Display produced by TOOTSIE in Run mode. 22 21000 keV. The numbers next to the arrows at each end of a spectrum are the limits of the expanded region. The number of counts in the highest channel of each spectrum is shown in the upper left corner of the spectrum. Below it is the number of the band, the bands being numbered from O to n-l, even though the limits in the Setup mode are numbered 1 to Zn. The numbers in the upper left corner are the same as those in Setup mode. 2.1.3. Ge(Li) Detector Efficiency Curves The photopeak efficiencies of Ge(Li) detectors are not constant with energy but generally decrease with increasing y—ray energy. The exact behavior of this decrease is dependent on many factors such as the total active volume of the crystal, the ratio of depth to width of the active region, and the source to detector distance. Therefore, in order to obtain the relative intensities of the y-rays emitted from a source, a photopeak efficiency curve for the particular detector and geometry used must be available. Efficiency curves for the detectors used in the present study were determined by using a set of y-ray sources, each of which emitted two or more y-rays whose relative intensities are well known. These sources were chosen to provide data points over the widest energy range possible, and yet, having each source overlapping, at least at one point, with another. This allows the efficiency curves to be bootstrapped to higher and lower energies. A list of the y-ray relative intensity standards used to obtain the efficiency curves is given in Table 3. Previous to this work on the efficiency curves, the data were fit to a straight line on a log-log scale. However, systematic deviations 23 Table 3. y-Ray Relative Intensity Standards Isotope Photon Relative Isotope Photon Relative Isotope Photon RelatiVe (Ref.) Energy Intensity (Ref.) Energy Intensity (Ref.) Energy Intensity (keV) (keV) (keV) 110mAg 446.78 3.5 5606 846.78 100. 182Ta 65.72 30.0 (c) 620.24 2.7 (b) 1037.83 14.0 (a) 67.75 430. 657.72 100. 1175.13 2.28 84.67 21.8 677.56 11.5 1238.28 67.6 100.10 119. 686.83 7.1 1360.22 4.33 113.66 17.7 706.66 17.2 1771.49 15.7 116.40 4.30 744.20 4.7 2015.36 3.08 152.44 71.0 763.88 23.9 2034.92 7.89 156.39 27.2 818.01 7.7 2598.58 16.9 179.39 31.7 884.66 78.0 3010.20 1.00 198.30 15.3 937.47 36.3 3202.30 3.04 222.11 79.8 1384.22 27.6 3253.60 7.41 229.26 38.0 1475.74 4.6 3273.25 1.75 264.07 37.6 1504.91 14.7 3451.55 0.875 927.70 8.00 1562.23 1.34 3548.05 0.180 959.11 4.40 1001.66 24.3 1“0La 109.60 0.22 1991r 136.35 0.15 1113.18 4.10 (a) 131.15 0.455 (a) 201.20 0.45 1121.19 370. 241.91 0.555 205.81 3.30 1157.41 11.0 266.53 0.510 295.94 29.2 1188.95 171. 328.75 21.6 308.44 30.6 1221.31 289. 432.54 2.95 316.49 85.8 1230.93 121. 487.03 46.5 374.40 7.70 1257.34 16.0 510.95 0.350 416.40 6.90 1273.67 6.90 751.66 4.50 468.05 50.5 1289.07 14.7 815.80 24.0 484.55 3.30 1342.60 2.80 867.87 5.70 489.10 0.510 1373.80 2.40 919.60 2.50 588.56 4.60 1387.20 0.810 925.25 6.70 604.40 8.90 1410.00 0.470 951.02 0.600 612.44 5.48 1453.00 0.330 1085.30 1.05 884.50 0.170 1596.20 96.5 1338a 53.17 1.95 2010.40 0.430 206Hg 72 11.9 (a) 79.59 3.04 2348.20 0.820 (e) 82 3.44 81.01 36.0 2521.83 3.25 279.2 100. 160.62 0.760 2547.70 0.090 276.29 7.50 20781 569.62 98.0 302.71 19.6 26Na 1368.53 100. (a) 1063.65 77.0 355.86 67.0 (a) 2754.14 100. 1770.18 6.4 383.70 9.40 24 Table 3. - Continued 177mLu 71.7 7.2 152Eu 121.78 332. 16016 86.79 209. (d) 105.3 100. (a) 244.70 72.0 (a) 197.04 65. 113.0 184. 344.27 314. 215.62 50. 128.5 131. 411.05 25.3 298.54 350. 153.3 144. 443.89 33.0 309.49 11. 204.1 117. 688.80 91.0 337.30 5. 208.3 512. 778.85 152. 392.43 19. 228.4 310. 867.42 51.0 765.20 17. 281.8 118. 964.00 173. ~ 879.31 400. 327.7 152. 1085.80 100. 962.46 140. 378.5 240. 1112.05 164. 966.17 344. 413.6 135. 1212.90 17.0 1002.90 16. 418.5 172. 1299.20 19.0 1115.16 21. 466.0 20. 1407.92 243. 1177.98 206. 1199.92 33. 5700 122.05 85.3 “636 889.30 100. 1251.30 1. (a) 136.46 8.40 (a) 1120.50 100. ’ 1271.90 103. 1312.17 40. 60C0 1173.23 100. 88y 898.02 92.0 (a) 1332.51 100. (a) 1836.13 100. (a) Gu69 (b) Ca7l (c) Ha69 (d) Be69a (e) Le66 25 of the data from a straight line suggested a third order fit of the form, log (efficiency) = A + B log E + C (log E)2 + D (log E)3, where A, B, C, and D are empirical constants and E is the energy in keV. (Gi69) A computer program was written for fitting the data to this equa- tion. Actually, the data are divided into two overlapping sections, one with energies above 6-400 keV and one with energies below 6.400 keV. A curve for each section is obtained by calculating the curve for one isotope, then for a second isotope, normalizing the two curves for the best overall fit, and finally repeating for as many isotopes as used. The curves for the two sections are then normalized at 400 keV. The final curves are good to about 3% for energies greater than 400 keV, about 5% for 100 keV to 400 keV, and about 20% below 100 keV. The increasing error results from the fewer points available, the rapid drop in efficiency, and the increasing complexity of the function at lower energies. The efficiency curve for our 10.4% Ge(Li) detector for a source at 10 inches is shown in Figure 7. This curve is for the detector without any absorbers. The shape of the curve can be changed, enhancing a particular energy region, by a judicious choice of absorbers. This is further described in Section 6.1. 2.2. B-Delayed a—EmissionpSpectrometer In order to examine the possible B-delayed 0 emission of the Ga isotopes, a different system of sample preparation and counting was required. Because of the short range of 0 particles, the sample needed to be counted in a vacuum and preferably from a massless target. Also the short half-lives of the isotopes studied precluded any manual handling 26 .uouooump OLD mo ucoum CH mmfiocH oH pmomHa moonsom ecu :DHB nouomuep ucmHOHmwm No.0H mzu pom m>uso xocmHOwam meQODOLQ m>wumHmm .m .me 365.85ch Sm?» 000m OOON COO. 00m OON 00. On A... .21.... .H ....H_ .l I. mw mflw 0.... .I I. Mm. i a n H6 m. m H m... I I. «la. I .. o. w A mmroz_ O_ .5. ION r KOFOMHMQ 24va o\o v.0. ...p_ p b .bP—_ 27 of the samples. The He-jet thermalizer was utilized to transport the activated nuclei from the vicinity of activation to another location in vacuum. This eliminated the possibility of any prompt 0's from the target being counted as well as produced a "massless" source for a particle counting. Any 0 particles were then counted using Si(Li) sur- face barrier detectors. 2.2.1. a-Particle Spectrometer The a-particle used in this study consisted of a Si(Li) sur- face barrier detector and its bias supply, a charge sensitive FET preamplifier, a spectroscopy amplifier, an ADC, and some type Of memory storage unit plus its associated readout. The Si(Li) barrier detectors used for the experiments were obtained from ORTEC. They had an active area of about 25 mm2 and a sensitive thickness of about 100 microns. Their resolution for the 5.545-MeV 0 particles of 21”Am was about 16 keV. For these experiments the detectors were used with ORTEC model 125 pre— amplifiers. The rest of the spectrometer system utilized the same equip- ment as the y-ray spectrometers described in Section 2.1.1. 2.2.2. He—Jet Thermalizer In order to determine the existence of B-delayed 0 emission, a system was needed to transport the activated nuclei quickly into a vacuum chamber in a suitable form to count the 0 particles. This becomes rather difficult, since the half-lives of the nuclei under investigation were expected to be on the order of 1 second or less. A He-jet thermalizer built by K. Kosanke (K070) at the MSU Cyclotron Laboratory was utilized for this purpose. The system thermalizes the 28 recoils produced by the interactions of the cyclotron beam with the target in ”1—2 atmospheres pressure of He. These recoils are collected with the He into a polyethylene capillary and transported at sonic velocities to the counting chamber. In the counting chamber, which is at :10-2 torr pressure, the He flow exiting the capillary diverges much more rapidly than the heavier recoils, thus allowing them to be collected on a surface placed near the exit of the capillary. This produces a "massless" source for counting with an a detector. Figure 8 shows a view of the thermalizer box. The cyclotron beam enters from the left and passes through a water cooled collimator. Mounted to the rear of the collimator are several teflon blocks con- taining an :1" ¢ hole. The target foil is placed between the collima— tor and the first teflon block and if more targets are used, they are placed between the teflon blocks. The recoils are collected by He entering the rear of the teflon blocks and being drawn past the targets into the capillary which is placed in the first teflon block. The beam is stopped in the water-cooled Faraday cup to the right of the collection assembly, while the capillary exits through the rear of the box. The recoil counting chamber is shown in Figure 9. The cap- illary enters the chamber through a port in lower right side of the figure. A Si(Li) surface barrier detector is in the cooled mounting and is connected to the coaxial cable connected to one of the feed— throughs in the upper right. A collector is placed between the detector and the port facing it. The port may be fitted with a thin plate so that the sample may be counted simultaneously with a Ge(Li) y-ray 29 Capillary Collimator Beam Entrance Target Holder Fig. 8. Recoil thermalizer showing target holder—collector and Faraday cup. Coaxial Cable To Vacuum System Fig. 9. Recoil counting chamber showing capillary and detector in cooled mount. 30 detector. The chamber is evacuated through the pipe located in the lower right corner. 2.3. Cu-Zn Chemical Separation Some of the experiments using Cu targets required a chemical separation to insure that only the Zn isotopes produced and their daughters were present. Because of the 38.4-min half-life of 63Zn, long involved procedures could not be used. The method utilized was found to be somewhat rapid, very simple, and efficient as compared to other methods. A 1"X1"XO.01" target was dissolved in a solution containing 5 ml 30% H202, 10 ml 6N HCl, and l meq Zn++ carrier. The solution was evaporated to dryness and the residue taken up in a minimum volume of 2N HCl. This solution was then eluted through a column of Dowex 1X8 50-100 mesh anion-exchange resin that had been previously washed with 2N HCl. Following this eluent, the column was washed with 2N HCl until no trace of Cu could be observed. The resin was removed from the column, dried, and mounted for counting. Chapter III DATA ANALYSIS Data analysis played a very important part in the development of the final decay schemes. Several programs have been used at MSU for the analysis of Y—ray singles and coincidence spectra. One program was used to sort through the data tapes from a megachannel coincidence experiment to produce several types of coincidence results. Some of the other programs were used to determine the energies and relative areas of the photopeaks observed. These results were then used by another program to determine the relative intensities of the y—ray transitions. Finally, these results were used in the computation of the necessary values used in a decay scheme. Section 3.1. describes the program EVENT RECOVERY, which is utilized to sort through the multimillion coincidence events to obtain the desired coincidence spectra. The pro- grams utilized for y-ray energy and area determination are described in Section 3.2. In Section 3.3. the program which performed many of the decay scheme calculations is described. 31 32 3.1. EVENT RECOVERY Proggam In Section 2.1.2.3. the task EVENT which was used to store the data from megachannel coincidence experiments was described. In the several years EVENT has been in use, several changes have been made in it. Some of the changes involved the three most significant bits of each data half word. Initially these bits were unused, but now they are used to designate the ADC producing the data address or to produce routing information. Also, the coincidence data may be used for y-sum coincidence experiments as well as y-y coincidence experiments. Since task EVENT only stores the data, another program was therefore necessary to sort or recover the data in the desired modes. The program utilized for this sorting is called EVENT RECOVERY. Since all the coincidence data are stored on magnetic tape without gating limitations, all the gating must be done by the recovery program. In order to perform this most efficiently, the program is a FORTRAN main routine, with most of the sorting being performed by a SYMBOL machine language subroutine. In this way, the data addresses may be stored in internal registers instead of core memory, thereby increasing greatly the rate of sorting the data. Basically, the pro— gram takes the two addresses of the coincidence event, places a digital gate on one address, and increments the location specified by the other address only if the first address falls within the digital gate. However, in order to perform this gating, many items of infor— mation must be evaluated. For each gate to be performed, EVENT RECOVERY reads one control card, with a limit of ten control cards per pass of the data tapes. The limit results from the core size of the Sigma 7 and 33 the amount of swapping of core pages involved. A flow scheme of this program is shown in Figure 10. After reading the control cards for a pass of the data tapes, the program starts reading the tapes. If the end of a tape is encountered while reading, the program then deter— mines if more data tapes are to be read. If no tapes are left to be read, the data are punched out and more control cards are read. If there are tapes left to be read, the program calls for new tape and then con- tinues reading data when the tape is mounted. When an event is read, the sum of the two addresses is computed and stored in a register for later use. With the two addresses and the sum address stored in registers, the program now checks the parameters on each control card: which of the three axes, x, y, or sum, is to be displayed, whether there are any limitations on the sum address, and which axis if any is to be gated. If the gated axis address falls within the background limits, a weighted amount is subtracted from the display spectrum, whereas if the gated axis address fall within the peak limits, the address in the display spectrum is incremented by one count. This process is repeated for this coincidence event until all the control cards have been checked. When all the cards have been checked, the process is repeated for each succeeded coincidence event until the last tape has been read. A com— plete listing of this program is found in the Appendix A. A four-dimen— sional version of this program is being developed for experiments using more than two parameters, such as y-y resolving time experiments. 3.2. Ay—Ray Energy and Intensity Determination The centroids and areas of the photopeaks in a spectrum were found by subtracting various order interpolated backgrounds from the 34 START READ CONTROL CARDS ..—_— FEAD EVENT FROM mp0 4 Y PUNCH END OF TAPES 5 DATA INC SUM ' XOY 7 I- SUM SUM LIMITATIONS SUBTRACT BACKGROUND SLBTRACT BACKGRCXN) EVENTS . J STORE EVENT Fig. 10. Flow diagram of EVENT RECOVERY program. 35 data. These computations were performed with the aid Of two spectrum analysis routines used at the MSU Cyclotron Laboratory: MOIRAE and SAMPO. 3.2.1. MOIRAE Spectrum Analysis Routine MOIRAE is a machine language task under the JANUS monitor that utilizes a Fairchild 737A live—display oscilloscope and sense switches to perform the spectrum analysis. MOIRAE was developed by R. Au and G. Berzens at the MSU Cyclotron Laboratory. A modified version of this task called MOD7 was developed by D. Bayer, also at the Cyclotron Laboratory. The primary difference between the two is that MOD7 utilizes a Textronics 611 storage oscilloscope for its display. The following description will be of MOIRAE but for the most part applies also to MOD7. The primary purpose of MOD7 is to alleviate the large amount of computer time used to drive the live display. All the analysis performed by MOIRAE is controlled by instruc- tions to the computer via interfaced sense switches arranged below the display oscilloscope as shown in Figure 11. Once the data have been read in from the card reader or transferred from a data acquisition task, the switches control the type of display, log or linear, expansion and shifting of the axes, various computational routines, and the outputs of the results. Figure 12 shows a closeup of the switches with labels for the routines they control. A display of the :1300 keV to :1500 keV region of the 63Zn spectrum is shown in Figure 13. The information across the top of the display gives the number of counts in and the channel location of the long pointer, the run number, the subroutine presently in use, and the order, up through 9th, of the background fit being used. If a log dis- play had been used instead Of this linear display, the number of cycles Fig. 11. MOIRAE display oscilloscope and sense switches. Fig. 12. Closeup of MOIRAE sense switches. 37 I... o I... Fig. 13. MOIRAE oscilloscope display of a portion of the 532m y-ray spectrum with a seventh order background fit. 1'00 0 I... Fig. 14. Display of peaks after calculated seventh order background has been subtracted. 38 would be displayed to the left of the run number. The background displayed with the data was determined by fitting all the points between each pair of short lines (BACK 2) inclusive to a 7th order polynomial. The sense switches were used to move the tall pointer to the position of the points used for the limits of the background regions, with the short lines indicating the points that have been accepted. Instead of using several regions for the fitting of the background, a set of individual points (BACK 1) may be used. The two tall lines indicate the points selected as the limits of the l412-keV peak, with the short mark indicating the centroid of the peak. Either the full raw peak (PEAK l) or the portion of the peak with counts greater than one-third the maximum (PEAK 2) may be used to calcu— late the centroid. In both cases the task then finds the centroid, area, sum Of the raw data and background, and the square root of that sum. This information may be punched on cards, printed, and/or plotted on a Calcomp plotter. Figure 14 displays the difference between the back— ground and the data displayed in Figure 13 in addition to the data. The points at the top Of the display indicate those channels with fewer counts than the fitted background. In order to convert the centroids and areas produced by MOIRAE into energies and relative intensities, the program MOIRAE E(I) is used. This FORTRAN program written by myself and D. Beery uses the card output from MOIRAE for its data. The centroids of several strong y-rays in the Spectrum are used to perform a least-squares fit to a quadratic energy Calibration curve. This curve is then used to calculate the energies Of all the peaks in the spectrum. Using these energies and a detector 39 efficiency curve calculated by the method described in Section 2.4., the relative area for each peak is calculated. The energies and relative intensities as well as all the input information are then printed. A listing of this program is found in Appendix B. The advantages of MOIRAE include the immediate operator con- trol over such parameters as background order, background points, and intervals and peak end points. This control is especially helpful for regions with complex or unusual background such as Compton edges. The disadvantages also become rather obvious. One is its inability to strip unresolved peak multiplets. Since no standard peak shape is used, another strong disadvantage is that, although the Operator has visual control of the analysis, the analysis of one y—ray spectrum may take 2 to 3 hours. Some of the disadvantages Of MOIRAE are also of the subjective type. Because the determination Of the background and the peak limits are under operator control, the choice of what background order and what collection of data points produce a good background fit can be difficult. Also, the choice Of how large a region to fit the background over and then what peak limits to use may be very difficult to make, especially if the peak has tailing. For an ideal peak of high intensity situated on a smooth background, a good low order fit is easy. However, for several closely spaced peaks, a peak on a Compton edge, or a peak in a region of poor background, what is the best background? In general, an ideal fit would be a linear background approximation; however, it seems reasonable that any single polynomial curve may be used as long as the background is fit smoothly and approximates the desired background shape 40 under each of the peaks included in the interval. A change in the back— ground shape changes the peak control only slightly while producing a much larger effect on the area. 3.2.2. SAMPO Spectrum Analysis Routine SAMPO is a FORTRAN program written and modified by J. Routti and S. Prussin (R069) at the University of California, Berkeley, and modified for use on the MSU XDS Sigma 7 by C. Morgan. It can be con- trolled either via storage scope sense switches and teletype or by FORTRAN control cards. This program utilizes the photopeak method analysis, with each experimental peak being fit to a Gaussian function having exponential tails. The mathematical evaluation involves initial shape calibrations using strong well-resolved peaks well-spaced over the region to be anal- yzed. The shape parameters are stored and a linear interpolation is used to Obtain the parameters for any other peaks under consideration. Once the shape parameters have been calculated for a given spectrum, for subsequent runs they may be reread directly into the program from FORTRAN control cards, thereby saving computational time. After a shape cali- bration has been established, an energy calibration curve using these and/or other peaks may be calculated at the Operator's discretion either by linear interpolation or by a linear or higher order least-squares polynomial fit. Similarly, efficiency calibrations may be performed using a number of well—spaced peaks and their relative efficiencies. The analysis by SAMPO of the data may be performed in two modes, "automatic" or "manual". In "automatic" mode, SAMPO searches out all the statistically meaningful peaks based on the calculated shape parameters, evaluates suitable fitting intervals, and fits the peaks 41 using the shape, energy, and efficiency calibration data. For peaks that fall below the minimum statistical limit for the automatic search, for multiplets that are not clearly resolved, or for any other peaks or regions of interest the manual mode may be used. In this mode, the fitting intervals and the peak locations are input and the program then fits these peaks similarly to the automatic mode. The program may operate entirely in manual mode if desired. Figure 15 shows a portion of the program's output for the l392—keV doublet from 63Zn decay. The plot displays the data, the cal— culated fit, and the calculated background. Above the plot are the upper and lower limits of the plot, and below the plot is the legend. The channel number, standard deviation of the difference between the data and the calculated fit, and the calculated background are printed to the left of the plot, while the data and calculated fit are found at the right. Below the plot is given the sum of the difference between the data and the calculated background and the sum of the difference between the calculated fit and the calculated background. For each peak fit, the program returns the centroid and its error, the energy and the error due to the calibration curve and the overall error, the fit peak area and its error, the fit peak relative intensity, the error due to the efficiency curve, and the total error. Since its inclusion into the data analysis program in this laboratory, SAMPO has proven invaluable in the time saved stripping multiplets. An example of its ability to strip multiplets including unresolved ones is shown in Figure 15. The deviation from the average energy over three separate 63Zn runs was less than 0.4 keV for the 42 ”.00.“ «.ooou “.maou uH-m o..~.~ o. onom o.on.u n.~c.~ 0.0”.“ mouunu nonnfln M..s.. 0.000” u.»ucw o.»»~u o..nan ....on o..aoa o..-au .....~ o.sna~ n.onnu c.3nau n..oo~ .. can » u» .muCOCOdEoo Hmst>chH muH 6cm umesow one Bosm cu cameo comp m>mn mocHH .mmoop ammo 60pm DOHnsop >0xINmMHI mmmH mzu mo uHm muH wcHaoLm omzmx. .>mx. .>my. .z».mpm»z. aau.».e ama< xoauzu aam.m.4«u >oamzu aoamu.».u game mxaua oz.mm.z use scan xomxo .oaoaeauooaza o. .oo.« . <1o.m «o aso~.- . oaaaom.xo a. human. mu»oo« or» tome meaamua a.ccn~« .UJ4up3m o.omn~. .<»m _.--: ~: 3 : __~...._~.~.._..~_.~_ ---~_..~._._ ..~__..~: Z Z.._-~. . . .«Hou .o a.ooo~ w. .noca .maou . «.ooou m. .Soou .oo. . ..~.o~ ... .nm.« .80. . “.m.u~ ~.. .mo.. .on-u .. o..~o~ o. .a».« .nnom . o.ono~ .. .0... .n on . o.omo~ a.. .as.. .0 on . . o.~oo~ A.” .o»:« o.“““ O Oohsnm Mon ohhcw .m o a . .nno a. o .05: oucun .Ill ellwolllllll. H Mommom cone .mhou a... . .. I .. a... ... a... m a» . III . a o. . s .nwno ; ‘0 ‘0 - ‘V ‘0 a “.550" c.“o oust“. o N. 9 o ' ' ' N ‘0 a OMOON 0o 0 cub.“ ."N‘. /o O ' ’ N ‘r ’ , H “omDQN no 00“.“ .nuaa . .IIIIqu . «.aomu 0.”. .08.“ .ooan 91117. . a.uoo~ 0. .s8.« .oaan . . u.n.m~ ~.~ .86.. .ouan .o. o.a.a~ n. .oooa .uoau . o. mas ~.. .co.. .Wonu .. m. aou o. .no.. «on . o.snm~ ~.. .msou .soau o n.noau .. .Hoou .aoau . n.m.m~ ~. .0... ooze Suo zHumHmm .oH .me mwmcommd an owo>m=> do... 2. COUNTS PER CHANNtL 52 x-Axus l E? A I a D I ; Y-AXIS Ioooo- 3'“ it 5“" CO'NC'DENCE- Ioooo- 3‘ 1: _ANY COINCIDENCE- / I: 30* I} gk’ 2 x"; (,2; 6400-' f E . 6400- ; 1 I _ G I ‘ § ‘ 8 3600-» g - \\ e * z 9 3 I600 " n a? -I L 1 400- : j“-JL’\hnq~d ‘ j I ()r ‘78 225- - Ioo- ~ I600- -I IGOOP' ' 900» 4 900. 400- ~ 400- I00- - IOOr 0 ~ A o J o 500 I000 o 500 I000 yANNEL NUMBER Fig. 17. Coincidence spectra forgz The integral coincidence spectra are shown in A and D. Gates were set on the spectrum in D as indicated by the bars, with E’ and F, same as B and C except that the background indicated by bar H has been subtracted. Spectrum 6 was produced by gating on the spurious "220—keV" peak. 53 more intense in this spectrum than the 669.7l-keV peak but is much weaker in the singles and any coincidence spectra, the 962.14-keV Y is shown to be in coincidence with the 449.8-keV Y. A new peak also appears at 220 keV. There was never any sign of this peak in the singles spectra, so further gates were used. Part C'shows the results of a gate on the 449.8-keV peak with a width four times that of BL Here the entire spectrum increases in intensity, but the peak at 220 keV has also increased greatly in width and is now much wider than the three known photopeaks. In parts E7and F'the results of background subtraction are shown. The background used was the region denoted by the bar EIbut excluding the regions in gates B and C', respectively. Region H is 50 keV wide and centered on the 449.8-keV peak. In spectra E'and P’ the 669.71-keV peak has disappeared, confirming our previous conclusion, but the Y1 and 962.14-keV peaks are weakly though definitely present. The 220-keV "peak", however, has increased greatly with respect to these and the regions on either side of it have gone to zero. This shows clearly that the Compton distribution in the gates was not only in coincidence with other regions of the spectrum in general, but also with this region in particular. By gating on the 220-keV "peak", as shown in spectrum G, new peaks appear at 290, 740, 895, and 1180 keV in addition to the one at 450 keV. These energies are 220 keV less than the strong yi, 669.71-, 962.14-, 1115- (552n contaminant), and 1414.1-keV peaks, corresponding to Compton-scattered Y rays from one detector being captured in the other detector. 54 4.1.3. Angplar Dependence In order to insure that the effects observed came strictly from Compton scattering between the detectors, further studies were performed with a 137Cs source. The effects of variations in the angle between the detectors on Compton scattering can be seen in Figure 18. The full-energy chance-coincidence peak is noticeably narrower than the large Compton edge and backscatter peaks. As the detectors are moved from 90° geometry toward the unfavorable 180° geometry, the increase in the Compton edge and backscatter peaks is very apparent, indicating that the primary direction of the Compton-scattered photons is back toward the source of the incident radiation. Table 4 gives the total, chance, and true coincidence rates. Calculations of these angular effects are well known. With EY as the energy of the incoming photon, E; that of the scattered photon, E0 the electron rest energy, and 6 the scattering angle of the photon, one obtains which has a maximum at 6 8 180°; E; is related to EY and E0 by For 13703, E; = 184.4 keV, which is the energy of the backscatter peak observed at all angles; in these close geometries the angular I37 Cs COINCIDENCE OOCEB 9.— 5? l20 DEG goo. . “oq’ 1 IOO- .4 Mr ISODEG 400’ COUNTS / CHANNEL ‘relTE I . 1 ISO DEG 4od' IOQI- LC L L 500 IOOO CHANNEL NUMBER Fig. 18. 137Cs Compton-scattering coincidence spectra showing the effects of the angle between detectors. 56 Table 4 137Ca Coincidence Counting Rates as a Function of Detector Angle and Absorber Usage. Angle Absorber Total cps Random cps Net Cp8 (RIRZT) 90° no 2.74 2.55 0.19 90° yes 1.51 1.33 0.18 120° no 9.84 1.85 7.99 150° no 10.95 2.21 8.74 180° no 12.08 1.61 10.47 180° yes 3.21 2.45 0.76 57 acceptance of the detectors is large enough to wash out most of the predicted angular dependence. .When a graded Pb collimator, as shown in Figure 16, is placed between the detectors, we see the effects illustrated in Figure 19. At 90° the huge Compton edge and backscatter peaks have been almost removed. At 180°, while not removed, they have been decreased to an almost reasonable level. This points up the fact that such collimators are all but essential for serious Ge(Li)-Ge(Li) coincidence experiments, but even they cannot insure completely valid results at close 180° geometry. These results are also included in Table 4. 4.1.4. Gate Widths Figure 20 shows the effects of varying gate width on the coincident backscatter and Compton edge peaks. The display spectrum (from the 2.5% detector) is shown in part A, while the gates (from the 2.0% detector) are shown in part F. In parts B through E the effects of the various widths of gates on the backscatter peaks are shown. The gates correspond to the regions denoted in part F. For the narrowest gate (in B) the Compton edge peak is about twice the width of the photopeak, and by decreasing the gate width even further, it could undoubtedly be made the same width as the photopeak. As the gate width is increased, the Compton edge peak broadens somewhat but does not increase in height. This is rather graphic evidence for the one-to-one correspondence between portions of the spectra resulting from Compton scattering between detectors. A similar effect is seen by gating on the Compton edge and looking at the resulting spectra, G through J. Notice the dip that 58 .oH .me cH sBonm mm pmomHa unnuomnw pm possum onnu BUINN.H m :uHs .uanu mfiu so mmozu muonuompm cm usonuH3 cmxmu mums ume one so muuuomm one .muouomuov mnu newsman umnuomnm :m wnHomHn mo muoommm any msH3onm muuomam mosmeosHoo wsHuouumom souano mommH .mH .me mmmEDZ JMZZY or X0; I N8 my... .. .. m ‘mWMVth; p M I .m 3.... u w ._H . r... M y l (on . m fl 1 I H a a... H m 1.. .. fl C\)/& L 648980 >24 r 82 > m . wbdo >9. I 00¢ ) 2 cN 8 ‘IBNNVHO 83d SiNflOO 73 shown. The integral or "any" coincidence spectra, which were obtained by adding up all the listed events recorded by the 2.5% and the 2.0% detectors singly, are shown at the top as X and Y, respectively. All that need be said about the decay scheme, which is described in Chap- ter 5, is that the first and second excited states of 63Cu lie at 669.7 and 962.1 keV, both decay exclusively to the ground state, and the weak 449.9-keV Y feeds the 962.1—keV state from a state 1412.1 keV. The 669.7-, 962.1-, and 1412.1-keV states are all strongly 8+ fed. The cascade nature of the 449.9-keV Y is demonstrated by the gated spectra appearing in the lower half of Figure 24. Placing a gate on the 450- keV region causes an enhancement of the 962.1-keV y over the 669.7-keV y, although the latter is more intense in most of the other spectra. Also, placing a gate on the 962-keV region results in an enhancement of the 449.9-keV y. It can be seen, however, that the background interference from the Y: (in true coincidence with 962.1-keV y) is quite severe in this last spectrum.' The spectrum resulting from summing each pair of X and Y addresses together is shown in Figure 25. Two types of peaks appear in this spectrum, sum peaks, as indicated, and Compton scattered peaks. The Compton scattered peaks are those that result from a Compton scattered photon from one detector being captured by the second detector. The peaks at 511.0, 669.7, 962.1, and 1115.4 keV are examples of this type. The peak at 1412.1 keV is mostly a sum peak but contains a Compton scattered component. 74 .cm .uHm mo unused» oouovHusHou HaywousH ecu sH usu>o mosuvHusHoo some mo oomaouvuu 050 models. 55 vouHuupo as: asuuuonu oHnH .nNmo you asuuooeu ousuvHosHOUIssu Hausa . OOON con. mums—Dz 1522410. , COO. 00m l1flbl°ITNG I #0... 'I V296'(Y"9 d .LUDO'CYHG Ir sIII OllG‘O’llS --—-====-.-.-—- a?) [699 j s”. ‘ (VHS J A No. .0. mozwo_oz_oo 23m :Nmm 'IBNNVHO 83d SiNflOO 75 Figure 26 shows examples of gating on each type of peak. At the top is shown the X and Y components of all sums with Y>X- The result is that the Y axis shows a relatively normal integral coincidence spectrum, although skewed toward higher energies, while the X axis shows a spectrum whose intensity is greatly reduced at the higher energies. Gating on the 669.7-keV peak (a Compton scattered peak) as displayed in Figure 25, the following results appear: A sharp peak appears at 511 keV in the Y-axis spectrum, and it appears to be in coincidence with a peak at ~160 keV in the Xhaxis spectrum. What is appearing is a true coincidence between the 511—keV photopeak from one detector with that portion of the y: Compton distribution from the other detector that is required to add up to the 670—keV gate. The peak at 2160 keV is narrow only because the gate on the 670—keV region was also quite narrow. In the 670-keV gated spectra three broader peaks also appear. The Compton edge from the 669.7-keV y in the Y spectrum is in coincidence with the backscatter peak from the same y ray in the X spectrum. And the broad Gaussian-looking peak that is split between the X and y spectra represents those portions of the Compton continuum from the Y: in each detector that, in true coincidence, add up to :670 keV. The spectra gated on the 511+670-keV sum start to show the ad- vantages of the sum-coincidence method. First, notice the welcome reduc- tion in the Compton background in these spectra. Then notice the clean appearance of the 669.7-keV photopeak in the.¥ spectrum and the 511.0- keV photopeak in the I spectrum. The 962.1-keV peak (weak) in the Y COUNTS PER CHANNEL 63 Zn SUM Xlflflfi' I ANY 511‘ Y2>X 3 -I 1 GTO'de GATE 4 4 5H06m0-kdv GATE .1 who so: Fig. 26. 76 COINCIDENCE 0‘ 03 Y 1005 I I ANY 511A V’>IX SOLD 669.? ’62.! _L 670 - keV GATE 5H'670-de GATE O CHANNEL NUMBER Sum-coincidence spectra for 63Zn. taken with the limitation Y>X, and the X—axis spectra are displayed on the left opposite their corresponding Y-axis spectra. All of the spectra shown were 77 spectrum arises from chance coincidences, as does the backscatter peak from the 669.7-keV Y in the X spectrum. In Figure 27 the results of gating on the 1412-keV sum peak are shown. The 449.8- and 962.1-keV peaks are very strongly enhanced, demonstrating conclusively that they are a cascade adding up to 1412 keV. The 511.0- and 669.7-keV peaks are present because of being in coincidence with the underlying Compton background. The fact that there is a 1412.1-keV ground-state transition is evidenced by the Comp- ton edge of this transition appearing in coincidence with its back- scatter peak. Subtracting a weighted background from each side of the sum peak improves the peak-to-Compton ratios further and removes some of the 511.0- and 669.7-keV peaks. Perhaps the strongest statement that can be made in favor of the sum-coincidence technique is "compare the 449.8-keV peak in the lower part of Figure 27 with the same peak in the 962-keV gated spectrum in Figure 24." The reader is reminded that both spectra were extracted from the same set of magnetic tapes. 4.2.3. Analysis of a Complex Spectrum: 20531 (in conjunction with K. Kosanke) A second example of how the sum-coincidence method can aid in resolving a weak, closely spaced triplet peak in the complex spec- trum is the results from the decay of 14.6-d 20581. The 205Bi singles spectrum presented in Figure 28 with its myriad of weak peaks, illustrates the complexity of the decay -- a total of 99 Y rays have been identified as belonging to this decay. The peak of interest here is the weak peak near 1002 keV. Figure 29, which shows only that small portion of the decay scheme (K071) necessary for the present discussion, 78 .3000 80m >mxIH.~HcH one so umm mumw saw one suHs ammo pom muuoomm mosopHusHooIabm .NN .me mg 492410 «8232 #22510 00.... 08. 08 o 08. 08. 08 o _=_«flfl v a o 1 0 fl 1 n 3 I SFBEhgm 950553 1.53 .40. I Shghmam 2619.040 1...; a 9 m . v r . .v v S . 0 o .o .. L a fi T A g I W m m I I In. I in gkuéhma 959.963 5.81:! zoFgg 2519.93 .5992; m . . o~ . m. on w_x< > m_x< x x A > WEB 55m >373! anm 79 VEGA Bi205 Singles LOW ENERGY REGION 0'1... O'IIEK I. 010.” ATOM-— ‘" I. ..‘.°|-.‘— A'COOI "’ I0£I~ . O'Otl .- “”0. s ”9' . 205 . BI SIngIes HIGH ENERGY REGION I' O.“ col" 0' O I O! I'OOOC I'IOII 0‘01.“ 4 51¢ fir 2'0. db ”0' «- 5|0° .. 'IBNNVHO 83:! I IO5 4» SlNI'IOO 510. 4 ZIO‘ ,. I I0‘ I I0‘ CHANNEL NUMBER 205Bi singles y-ray spectrum taken with a 7 cc Ge(Li) detector. Fig. 28. BO ? s 55% §=:§ 4:- , .. ,66' 38% g; an: o. " " ”64.5 = 53 _.s- g _ 1 now 1' mm 2 . " 233% £3 3 3 5 , I264.5 " .75 3 a .5' was: I: . 907.5 " a II .. “.3. g S :5' 2g 6 nm E v 2 IL 703.4 .5 as V p " A 5765 n 2 In B 202.9 2.3 / 7' o.o Fig. 29. A small portion of the 20581 decay scheme showing those states and transitions of interest to the present discussion. The three components of the =1002-keV triplet are drawn as larger arrows to aid the eye in locating them. 81 indicates the reason for selecting this peak. All of the previous studies of this decay (Ru71) concluded that the 1002-keV peak represents a single y-ray that feeds the 262.9-keV state. And although a slight broadening of the 1002-keV peak was noted, even the best Ge(Li) de- tectors did not have the ability to resolve the peak even partially. In our studies, however, considerable Ge(Li)-Ge(Li) y-Y coincidence data suggested a triplet with the placements indicated in Figure 29. To substantiate the tentative placements of the transitions in the z1002-keV triplet, sum-coincidence gates were set on the regions corresponding to the 1264.5-, 1705.0-, and 1764.5—keV states. The integral or "any" sum spectrum is shown in Figure 30. There are relatively few clearcut sum peaks in this spectrum, considering the wealth of cascade y-rays resulting from 20531 decay. In fact, examining the positions of the three sum-coincidence gates does not lead to much initial optimism. The position of the 1264.5—keV gate shows no sign of an obvious sum peak -— all that is present is a Compton-type background. At the location of the 1705.0-keV gate there is only a weak peak. Only at the location of the 1764.5-keV gate is the sum peak obviously present. The spectra resulting from these three sum-coincidence gates is shown in Figure 31. Only the composite spectra from the Y axis (the 3.6% detector) is displayed, with the small arrows indicating where X>Y ends and y>x begins. Even though the sum peaks were small in Figure 30, the gated spectra in Figure 31 show many well-defined peaks. A closer examination of each of these indicates that only a few are in coin- cidence with other y rays, while most of them result from Compton scattering. .Hmmom mom asuuummm mocmvwocaOUIESm :kcm: no Hmuos .om .wfim mum—2:2 1522410 82 S :_ fl . .2 z _ E e . n .“M: _ . ,H.A.. _., —u . .H .. e. . . 88 88 88 80m 89 08. q f _ _ 9 VDI me I it” ;un x A > .28 >z< a... 'IBNNVHO 33d SlNflOO 83 .3..qu MA was ensue kvm 83.233 05 sue...— to... ozone Sale 05. .9333 Swath Ed was sauna Jase.— Isa >873: use :60: .133 as» so wouusa no 3163 on» anyone Snow new unused. oosuvwosuoun-Bm 4n .3» mug-.2 4m22938. m 4 8 p p b p p b m.x< > uozweozao g .0 84 In the top spectrum, resulting from a gate on the 1264-keV region, the 1001.8-keV Y is shown definitely to be in coincidence with the 260.6-262.9-keV doublet. Also present is the 576.5-keV and 685.5— keV coincidence pair. Both the 561.6- and the 221.2-keV y's are too weak to stand out from the background in this spectrum. Also present in the spectrum are strong Y rays such as those at 549.8, 570.9, 703.4, and 1043.7 keV, which are present because of chance coincidences and because of Compton scattering, as discussed in Section 4.1. The other peaks in the spectrum are caused almost solely by Compton scattering, as was verified by increasing the gate widths and observing the resulting changes in the intensities and shapes of these peaks. The middle spectrum, resulting from a gate on the 1705—keV region, is considerably simpler. The 1001.6-keV and 703.4—keV coinci- dent pair is definitely established, and so is the 717.4-keV and 987.5— keV pair. Both the 661.3— and the 205.8-keV y's are too weak to stand out in this spectrum. A few more peaks are present in the bottom spectrum, gated on the 1764—keV region. The 1003.1-keV and 759.1-761.4-keV and the 720.6-keV 1043.7—keV coincident pairs are readily observed. Also present are the 703.4- and 987.5-keV'Y's, here only in coincidence with the Compton background in the gate, for their intensities are much lower than in the 1705-keV spectrum. In the spectrum drawn at the bottom of Figure 31, the 1501.6-keV and 262.9-keV coincident pair is not seen even though it is moderately intense. However, when using a wider gate width (:20 keV), this pair was easily seen. This result points out one of the problems that has not been completely solved here -- 85 that of unmatched gains for the two detectors. These peaks were far enough away in energy from the other two coincident pairs that their sum peak produced simply by adding channel numbers was excluded from the narrow sum gate based on the other two pairs. In this instance the apparent difference in sum energy was almost 10 keV. Thus, although one can and does use detectors without perfectly matched gains, he must be on the lookout for this sort of sum-peak "jitter". That is, unless he is willing to convert the spectra from channel numbers to y-ray energies before setting the sum-coincidence gates, a somewhat tedious procedure but one that can be performed readily by the computer. Accordingly, the presence of the 260.6-262.9- & 1001.8-keV, the 703.4— & 1001.6-keV, and the 759.1-761.4 & 1003.1-keV pairs in the sum gates set both confirm the existence of the z1002-keV peak as a triplet and also the placements of its components. Perhaps it is worth noting that the sum-coincidence method also added a confirmation of the new state at 1705.0 keV and by removing ambiguities in the y-Y coincidence results has allowed the definite placement of the 720.6-keV transition, the center member of a quite weak 717.4-720.6-723.6-keV triplet. 4.2.4. Conclusion It has been shown that the sum-coincidence technique as applied to the digitally-stored data from a two-dimensional Ge(Li)- Ge(Li) y-y "megachannel" coincidence experiments is a viable and useful tool for the nuclear spectroscopy laboratory. When thus applied, using sum-coincidence gates to complement the standard y-y coincidence gates in the off-line sorting of the spectra, the sum- 86 coincidence method is quite useful for pulling weak peaks out of a strong Compton background. The analysis of spectra must be made care- fully and cautiously, however, for the spectra resulting from sum- coincidence gates are not quite so easily interpreted as those resulting from standard y-y coincidence gates. This is particularly true when there is significant Compton scattering between the detectors. Nevertheless, when used to supplement and complement these y—y coin- cidence experiments and not as a stand-alone technique, the sum- coincidence method should find considerable use in high-resolution y-ray spectroscopy. CHAPTER V DECAY 0F 63Zn 5.1. Introduction The first report of the decay of 63Zn was by Bothe et al. (B037) in 1937, who produced it by the 6l‘Zn(n,27’t)63Zn reaction. Since then it has been studied by many groups. Most of the y-ray work has been performed by stripping y-ray spectra obtained from NaI(T1) detectors and comparing the results to the more precisely measured levels obtained from charged particle reactions. Since the advent of Ge(Li) detectors, several authors (H066, De67, Bo69) reported y-ray spectra obtained with Ge(Li) detectors a few cubic centimeters in size, each reporting more and more precisely measured 7 transitions than the previous authors. Kiuru et al. (K170) presented results obtained using a relatively large Ge(Li) detector that are in good agreement with previous results. The only coincidence results reported on 63Zn are from a NaI(Tl)-Ge(Li) coincidence experiment performed by Borchert (3069). Many charged particle scattering reactions have also been performed to study the excited states of 63Cu. Since 63Cu is stable as are many of its neighbors, a large variety of reactions have been performed. Some of the reactions performed were 63Cu(p,p') (Ma57), 62Ni(T,d) (3165), 6“2n(t,a) (3367), 62N1(a,t) (R068), and 62N1(d,n) (Ma7l). A comparison of the results from the different reactions and the y-ray studies is shown in Figure 32. 87 88 33 .2wa .\m. u\_ TL in uh. in ..\\u I\w TIN Ill-Ila." u\m 1) Em it {m u\_ IJII Aim {3 >22 2. 3.2 8 Km ¢\m 1...ch .\m cm -\_ in in {m - \h in in .somm CH woumum wouwuxm hUSum ou mom: chHuomou msOfium> mo upmaesm < 6.32% Km .2 .\m \N K. +\m -\. .\m K. xm0>> Fzmmwma -xm -\_ .\m -\N .\m in «9-3.: IHIIIJ-Iludll in in .\_ )2 .> int-\m km in in - "3.3.5 lllllhl. . . Corgi. Em {mfimfi Illllll. « u .a\fl ‘ IV“ llllllimcni {m in “x. .mm .wam 3,2 as 89 5.2. Source Preparation The 632a sources were prepared by bombarding natural Cu foils (69.09% 63Cu, 30.91% 65Cu) with protons from the Michigan State University Sector-Focused Cyclotron; these protons were degraded from higher energies to 12 MeV by the use of A1 absorbers to induce the 63Cu(p,n)63Zn reaction. Typically, lO-mil Cu foils were bombarded for :3 minutes with a typical beam current of :2 0A. The sources were allowed to decay for several minutes before being counted for several half-lives. More source was added with the passage of time to retain a relatively constant counting rate. To insure that only radiations from 63Zn were observed the y-ray spectrum was confirmed by counting sources that had been chemically separated according to the procedure in Section 2.3. 5.3. Experimental Results 5.3.1. y-Ray Singles Results Energies and intensities of 632m y rays were determined using the 10.4% efficient Ge(Li) detector. The energies of the prominent Y rays were measured by counting 632m sources simultaneously with 110'mAg and 5600. The energies of most of the weaker 63Zn y rays were then determined by using the energies of the prominent 632a Y rays as second- ary standards. The centroids and areas of the photopeaks were determined using the computer program SAMPO. A typical y-ray spectrum is shown in Figure 33. Forty—four y transitions were assigned to the 63Zn decay, and their energies and intensities are listed in Table 5 along with those of other authors (H066, De67, Bo69, K170). Also included in the table are the levels observed in the (p,p') reaction (Ma57). The uncertainties in the energies listed in 90 9'09; 3 M—“".§;; ' ' 0 L692 Z.L|LZ mW:~=-?:: I | . - ._— I. ”It. . 0 5‘3; ': ' (ungruwz- ~==af3égp c: H. 29am _:?“*=$33 "J\J ét€§:“;=2§ii m 9.9”? f“. 892922 Y us )suxz '{ ”R osmzjfi ttosflQEL' €29&?na_4bsaxn 69am .-zivoa owns 6 ( 194,03) 1'69“? ( a”) row 07.693 0 3500 2500 3000 2000 I500 The insets show the regions at 1392 keV and 1865 keV in more detail. CHANNEL NUMBER 000 o l l I ’1 {a E —- (“23.—ng Asam¢::::. 3099‘::’._.’ N ”g L, 1 L, L .g g Q m a) Is :9 n- gnx ”796 F I F 'I 1 I 7; § _ ,.{~§ TZGCI'=?1~-_ .v I 1’ fig twufl*::? ‘ l l 1 l l _'L g IO’IIS 3 Q :3 .n v ,0 .3. 1 l l h N — 9 o g 500 63Zn y-ray spectrum. Fig. 33. 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L . IIII IIII IIII IIII no.0 ~.o 0.0“ s.nooa nunoma AN 0+on o o H+¢ mama no o+mm o n o+~ mood IIII IIII IIII IIII Hmo.o“e~.o 0.0“ o.oomd m «a m at. m 1- w 1- m H m .me as «usual muonsaom a snag“ uuosouon .Hs as uncommon a moon a xuoa uooeoum azaasxo - m 0,—5.8 93 Table 5 are based on the uncertainties in the energy standards, the heights of the peaks above the background, and the reproducibility of the calculated energies of the different spectra. The relative inten- sities listed are averaged from several spectra, and their uncertainties are based on the reproducibilities of the intensities and the uncertain- ties in our experimentally-determined efficiencies for the detector. They are in general 50% greater than the largest deviation of a value from the average of several runs. The y-ray intensities of the other authors were renormalized to the 669.7l-keV y while retaining the original number of significant figures. A comparison of the present results with those of other authors, especially Borchert (8069) and Kiuru et a1. (K170), shows good agreement among the authors. The results of Holmberg et al. (H066) and DeFrenne et a1. (De67) will not be further discussed since their results have significantly fewer peaks than the others, even though their results are in generally good agreement with the others. Borchert reports seven transitions not observed here or by Kiuru and Holmberg, while Kiuru and Holmberg report only one transition not observed by other authors. In the present work, nine transitions were reported that were not observed by other authors, while five others were observed only by Borchert. Shown in one inset in Figure 33 is the 1360-1420-keV region of the 63Zn spectrum. Notice here the broadening of the photopeak at 31390 keV in comparison to the photopeaks on either side. This broadening on the low energy side is better shown in Figure 15. Because even our best detector could not resolve the 1389.5- and the 1392.3-keV components of the doublet, the program SAMPO was used to strip it, and the results are included in Table 5. The other inset shows the two resolved peaks at 94 1860.9 and 1865.7 keV. These are both full energy y rays, and neither one of them is the double escape peak of the 2889.5-keV 7, since both are much stronger than any double escape appearing in the spectrum. 5.3.2. Ge(Li)-Ge(Li) Mggachannel Coincidence Results The decay of 63Zn was also examined using the two-dimensional Ge(Li)—Ge(Li) megachannel coincidence system described in Section 2.1.2.B. For this experiment, the 2.5% efficient and 2.02 efficient Ge(Li) detectors were used as the x and y detectors respectively. The angle between detectors was 1:150 degrees. In Figure 34 some of the results are shown, where Figures 34A and 34E are the x and y integral or "any" coincidence spectra, respectively. Table 6 gives the y-Y coincidence results, in addition to those of the other coincidence experiments. Figure 343 shows the results of gating on the 450-keV peak. This gate produces a 962-keV peak greatly enhanced with respect to the 670-keV peak even though the 670-keV peak is stronger in both the singles and integral coincidence spectra. Therefore, the 962-keV y is clearly in coincidence with the 450-keV y. Also observed is a peak at 220 keV which results from a Compton scattered y-ray from one detector being captured in the other. This was discussed further in Section 4.1. The next gate, 511 keV, is shown in Figure 340. The y-rays appearing in this spectrum indicate the states that are 8+ fed. Feeding to other states is too weak to be seen in this spectrum. Further results on 8+ feeding to states are given in Section 5.3.4. Gating on the 670-keV peak, Figure 34D, shows only the 511-keV y from the 8+ feeding. Although there is a continuum at energies above 511 keV, no y transition to the 670-keV level is strong enough to be observed. 6.3 95 Z,“ CQNC'PENCE IOOOO» A 3 ’ q. 8 )V 3. W9 3”" g x AXIS ANY COINCIDENCE 6400 I E - ‘- ; ‘ . n ‘ . 1 0‘ I ' 3600* '3 '. )3 5'. ...' “3' 4 Q, : sass-5.4g. s 33 .. \2 §mmn 7* g. 9; 1500* .3.- .. ...-:2 up}, I g T ',= . 1 . _ ' 1 . .%;t:fn -4. E 400 P E JEN .3 52:25:55; ' ~ 35.-2'3" .'.:: i 3. - ....-. ...... r _ } 450 keV GATE I44~ T. d T __J £ 4 [-1—] - u - a. 0 Z I ‘ EEE-44oo ffllkéVW3ATT§ I ’- 4 Q \ IOOOO- - J <0 1. ...— Z 6400- 4 § 3600» _ ‘ , ., I " l . E} I 400?- e T cal—g w ‘4“ * 576 r E 670 keV GATE 4 324 ~ ‘ I44 - . 36r- M Jr 4 f wiW‘lfiunhH-l _._ -. . . ..-. L 4 J 0 500 1000 I500 2000 2500 3000 Fig. 34 (Part 1). CHANEL NUVBER 63Zn y-y megachannel coincidence spectra. In the top of this Figure and of Part 2 are shown the integral coincidence spectra, and in the lower portions are shown the various selected gates. COUNTS / CHANNEL 96 63 Zn COINCIDENCE r 1 1 F .....E a ,I. 6400L 3600r- IGOO" : \J}5 . .-S I0. .0. n44» 5V3 g Y AXIS ANY 0 l " "9 “2:? g COINCIDENCE - r .36. j E 33% . - ‘f’ WM. é‘i { 5E25hfaifi;a fl 4 1 8 99%5L.'. 6 ’ ‘1 t 2 “gags-3:??? :. . . : : Q 400* : tit“:- . '%’£:-‘:‘:~:-::.:..- .-.;-;-.-...-. ...... ‘2‘ ~ - 4- “\J 71°12:- _...... - :—-:::.:' ...:....‘t- ._ Hi ‘ " - .__ »F l 962 Kev GATE WM°.-L.-~4. .5. .. ...... . -.-;...- I 1040 KeV GATE l ._ ...-...-..- ...l- ..- .. . .. ... .-. - 47* H , 1392 Kev GATE 0 -_.__..--___- - -.- Iéiflzfn~an >oxu~uc~ >oxa~ona >uxuanoH >oau~oo >oxaoho >oxnaan poxnonc Iaan oooovaooaouuuo< uoawoum moauuucoucu o>uuuaou A>oxvrm mucolwuonxm oucovuucaou ow cans » sung uo acquaucouou o «An-a 98 Figure 34F displays the results of gating on the 962-keV peak. Here the 450-keV y is greatly enhanced with respect to the 511-keV y, indicating again the 450-keV y is in coincidence with the 962-keV y. Gating on the lO40-kev y shows, in Figure 340, a spectrum similar to the singles spectrum, but greatly reduced. The appearance of the lO40-keV y in the singles spectrum is debatable, since it would appear on a Compton edge. It also does not fit anywhere in the decay scheme and is probably a strong background peak that is in chance coincidence with the strong peaks in 63Zn. The gate on the 1392-keV peak, Figure 34H, shows a coincidence with only one y, the one at 670 keV. This confirms the placement of it as feeding from the 2062-keV level to the 670-keV level. Finally, Figure 34I shows the results of gating on the 1412—keV peak. Only the 511-keV y from the 8+ feeding appears. No other feeding to this level is strong enough to be seen. Gating on the remaining peaks in the x and y integral coinci- dence spectra show very little if anything. The l472-keV gates show possible coincidences with 270- and 511-keV y's. The 1547-keV gate shows only random coincidences and no firm indication of its 3+ feeding. All the counts in this gate were below 550 keV. The other gates are similar in that all the counts appear below 1000 keV. No channel in any of these gates has more than one count in it, and the channels with counts are randomly spaced. The peak at 2754 keV in the integral coincidence spectra could be from 21‘Na in room background and the Pb collimator. 5.3.3 Anticoincidence Results An anticoincidence experiment was performed using a 20.3X20.3- cm NaI(Tl) split annulus, a 7.6X7.6-cm NaI(T1) detector, and the 10.4% 99 efficient Ge(Li) detector, with the latter two detectors placed in opposite ends of the annulus tunnel. The y rays observed by the Ge(Li) detector were counted only when there were no y rays observed in any of the NaI(Tl) detectors. A description of the system and the electronics was given in Section 2.1.2.A. A spectrum obtained using this system is shown in Figure 35, and the results are included in Table 6. Most of the ground state transitions observed in this experiment were enhanced over their singles intensities. One of those not enhanced is the 1327-keV y. This is because the 1327-keV state has no 8 feeding because of the large difference in spin between it and the 63Zn parent. As a result this state is fed completely by Y transitions from higher- lying states. Other ground-state transitions not enhanced were at 1861, 1866, 2012, 2081, and 2092 keV. All these transitions were weak in the singles and were very weak in the anticoincidnece results. Of special interest are the 1861- and 1865-keV y peaks. It was expected that one of the peaks would be enhanced over the other to indicate which is a ground-state transition from a state at the same energy and which is a possible cascade transition. However, even though neither was enhanced, the relative intensities of the two to each other remained near that of the singles spectrum, indicating both transitions are of the same type, either ground state or cascade. Since other weak ground-state transitions of similar energies showed similar enhancements to this pair, these two peaks both appear to be ground-state transitions. 5.3.4. 511-511—keV-Y Triple Coincidence Results A Sll-keV-Sll-keV—any 7 triple coincidence experiment was per- formed using the 20.3X20.3-cm NaI(Tl) split annulus and the 2.5% efficient 100 T I T r I ] . ; 1 4i . 5' 20012 .... . ; - UJ . w_..e ! .. O owos ”Ti? ; i 4 2: .fi‘ ' LU 96882 ......- -:::i o BZQBmegifij; ' '5 a 9'092214913327a5ii31 ' 8 E 01592 . 3.4143 11'“: 3.3:;- :."3 ,..:‘ié o «“3" P 2 (llmeIQZ mg. _+ .— 29992 "'2“"""-’- z“ ” Z 92' Z ".54 .. QLGbZ . <1 x 89922 ...-:53, # VQHZ q VINE . — '3:- zzvoz :3? 0302 EH26 19%| 3 6‘ I r- -1 922»: ' - -4Qifl?l*-~1. EZGEI Wm___ 0129- p -+ CMS‘ME g6?” scan (Uzggvsm __ bl.296 "'“m'rzzaz, KJHQ *- —1 L, J 1 L l l [s 9 f2 '22 so ,2) NO .9 _ WBNNVHO 83d SiNfiOO 2500 3000 3500 2000 CHANNEL NUMBER An anticoincidence spectrum from the decay of 63Zn. IOOO '500 500 Fig. 35. 101 Ge(Li) detector. The two halves of the annulus were operated separately and each was gated on the 511-keV region. A triple coincidence was required between the two annulus halves and the Ge(Li) detector in order to count the y-ray observed by the Ge(Li) detector. A further description was given in Section 2.1.2.A. A spectrum obtained from this experiment is shown in Figure 36, and the results are included in Table 6. The experimental results show 8+ feeding to the 670-, 962-, 1412—, and 1547-keV states. An upper limit of 0.02% has been placed on the 8+ feeding to the l327—keV state. All states above 1547 keV are fed too weakly to be observed in this spectrum. A comparision of the mea- sured 8+ feeding to the states to those predicted from calculated eK/B+ ratios (Le66) is given in Table 7. The experimental values were nor— malized to the predicted eK/B+ ratio for the ground state and the ratio of the 670—keV Y intensity to the 511-keV intensity as measured by Borchert (3069). The differences between the experimental and theoretical values for the first two excited states is small, but it is very large for the other two B+-fed states. This is another case where the appar- ently allowed 8 decay is "hindered" as indicated by the lower than predicted 8+ feeding. A further discussion of the nature of these levels is given in Section 5.6. 5.4. Decay Scheme Figure 37 shows the decay scheme deduced from our experiments. Transition and excited—state energies are in keV, with the adopted energies for the levels being a weighted average of several experimental runs. The Qe Of 3364 keV was obtained from 63CU(p,n) measurements by Birstein et al. (8166). The total transition intensities, in percent of total 63Zn decay, are given in the decay scheme. Since all the internal .pOuomumU nfiqvmo ucmwofiwmm Nm.N mnu vcm mSHDGCm Aawvaz mnu wcfim: vocfimupo Esuuomam mocmvfiocfioo maawuu >IHHmIHHm < .om .mwp MmmZDz Amzz02 113 within a factor of two was also reached for the ICMl) for these transi- tions, poor agreement was reached for the magnetic dipole moment. Gove (G063) applied the calculations of Bayman and Silverberg (Ba60) for coupling a j=3/2 particle to quadrupole surface oscillations to the case of 63Cu. These calculations are in good agreement with the observed B(E2)'s. Harvey (Ha63) extended the Bayman-Silverberg model to the magnetic dipole moment and transition probabilities. He obtained good agreement for the dipole moment and for the B(Mfl) for the transition from the 962-keV state, but his results were a factor of four faster than the B(Ml) experimentally obtained for the 670-keV transition. A strong coupling model was used by Thankappan and True (Th65). The even—even 62Ni core which performs quadrupole surface oscillations was coupled by a quadrupole interaction with a dipole element added to the single proton in the 2p3/2, 2p1/2, and lfs/2 orbitals. Only the 0+ ground state and 2+ first excited state of 62Ni were considered in this calculation. Parameters also used were the orbital spacings of Bouten and Leuvén (B062), however, these were adjusted for better agreement of the calculations with the experimental results. The agreement for the calculated B(E2)'s with experimental results is good, but the fits of the B(Ml)'s vary from good to very bad. Also, the quadrupole moment is in good agreement as is the dipole moment. Beres (Be66) used a very different model, namely he described the core as a quasiboson of angular momentum 2+ and the odd proton as a quasiproton of spins 1/2-, 3/2-, and 5/2—. The core and the quasiproton were coupled by a quadrupole interaction. The resulting calculated B(E2)'s were in general agreement with experimental results. He also calculated the case of two quasineutrons interacting via a quadrupole 114 interaction with the quasiproton. This method gives a large number of low lying levels, and the collective quartet appears very closely spaced at about 2 MeV with the B(E2) values for this quartet in agreement with those of the other method. This method, however, gives much better agreement for the higher lying positive parity states in 63Cu, and good agreement is also obtained between the calculated inelastic a scattering cross sections and those observed experimentally. The model used by Kisslinger and Kumar (K167) is a modified phenomenological vibrational model with its microscopic description in terms of the pairing-plus-quadrupole model. This involves the coupling of the vibrational phonon with a quasiparticle with a quasirandom phase approximation. Simons and Sundius (Si69) used a vibrational core with up to three phonons coupled to a single particle in the 2p3/2, 2p1/2, and lj“5/2 states. They treated the phonon energy as a free parameter and obtained values somewhat greater than those of Bouten and Van Leuvén. They obtained a reasonable fit for the magnetic dipole and electric quadrupole moments, and the fits to the B(E2) and B(Ml) for the 670—keV transition are reasonable. However, the B(M1) for the 962-keV transition does not fit well at all. A semimicroscopic model of coupling the proton to a quadrupole vibrator was used by Paar (P370). The vibrator was allowed up to three phonons and the proton states included the 2p3/2, 2p1/2, 1f5/2, and 1f7/2 states. The lf7/2 was included since experimental results indicate that the 1f7/218 not a good closed shell in this case but is partially empty producing a partially filled 2p3/2 state. Reasonably good fits were obtained for the B(Ml) and B(F2) values and for the magnetic dipole and MeV 20 '4 1.5 r 05-1 00‘ 5/2 (5W2) 5/2.7/2- * 5/2- (v2) 5/2 59 Cu Fig. 39. 3/2- (7/2') 3/2- 5/2- 7/2- 5/2' v2‘ 3/2- 6|Cu Systematics of the odd mass Cu The results shown are from ND. 115 via? 7/2' 3/2’ 5/2- 7/2 5/2 v2‘ 3/2' 63 Cu 3/2- 5/2’ 7/2‘ 5/2' v2" 3/? 65 Cu isotopes. 3/2’ 772' 5/2‘ l/Z- 5/2 U?‘ 67 Cu 116 electric quadrupole moments. Wong (W070) performed shell model calculations for the 63Cu using a weak coupling model with the 2p3/2, 2p1/2, and lf5/2 orbitals for the proton. The energy levels produced by the shell model calcula- tions are in poor agreement with the experimentally determined energy levels. The fits for the B(Ml)'s and B(E2)'s were only fair, although better agreement was reached for the magnetic dipole and electric quadrupole moments. The intermediate coupling model developed by Thankappan and True (Th65) was used by Larner (La70) to calculated the states in63Cu. For the calculations, Larner coupled the 0+ ground state and 2+ first excited state of 62Ni to the 2p3/2, 2p1/2, and lf5/2 orbitals with an interaction that contained both dipole and quadrupole terms. For the first case, he used the experimental energy levels and single-particle strengths as input parameters, while the second case used the experimental energy levels and B(E2) values. The results of both cases gave similar good fits to the energy levels, and the first case also gave good fits to the B(E2)'s. Although most of the calculations agree on single particle admixtures, they are in disagreement with the experimental results. In particular, everyone except Paar (Pa70) assumes that the 1_1"7/2 shell is a good closed shell. The experimental results indicate the l327-keV 7/2- state has a 6% single particle admixture which would come from the lf7/2 closed shell. This agrees with the results of Goode et al. (G069) which indicate that 56Ni is only 94% a doubly closed nucleus. Figure 39 shows a comparison of the levels of the odd mass Cu isotopes. A comparison with the other Cu isotopes indicates the l400-keV level in 59Cu may be an unresolved doublet of a 5/2- and a 7/2- level. In general, the excited states rise in energy with neutron number. CHAPTER VI DECAY OF 62Zn 6.1. Introduction The odd-odd nuclide, ggCuBB, contains a single proton and five neutrons outside the doubly closed lf7/2 shell. Consequently, its states should be amenable to interpretation in fairly straightforward shell—model terms. Also, many states and trends in nearby odd-mass nuclei are known, providing reasonably trustworthy input for predicting the properties of its odd-odd states. Unfortunately, relatively few states are known in 62Cu itself, and even fewer have been well characterized. Here, the decay of 9.3—h 62Zn to 62Cu has been reexamined using the largest Ge(Li) detec- tors the laboratory has been able to obtain in order to pick up weak 8 feedings that previously have gone undetected. The findings are then correlated with those of previous investigators and with the data from scattering reactions in an attempt to obtain a more coherent understanding of the structures of the 62Cu states. Since the discovery of 62Zn by Miller et al.(Mi48), it has been studied by many other groups. Hayward (Ha50) determined the end—point energy of its 8+ spectrum to be 0.66:0.01 MeV and observed K and L conver— sion electrons from the 41.810.8-keV transition, the K/L ratio indicating it to be E1 or M0. Nussbaum et al. (Nu54) determined that the first excited state of 62Cu lies at 41.310.3 keV and that 36i3% of the 622n feeding passes through this state. From GK and K/(LfM) they assigned the 41.3-keV transition an M1 multipolarity. The first reasonably complete decay scheme was formulated by Brun et al. (Br57) who performed extensive electron and NaI(Tl) y-ray Spectroscopy, including coincidence and Y-Y angular correlation 117 118 experiments. They deduced states in 6?Cu at 0, 0.042, 0.30, 0.55, 0.63, and 0.70 MeV. In the last few years there has been a flurry of activity about the neutron-deficient members of the N=62 mass chain. Four groups (An67, R067, Ba68, H069) have reported Ge(Li) Y-ray studies on the decay of 62Zn, and two other groups (Jo69, Va70) have reported on the decay of 9.9-min 62Cu itself. Antman et a1. (An67) performed the first high—resolution Ge(Li) Y-ray experiments (in conjunction with electron experiments), and they and Roulston et al. (R067) demonstrated conclusively the doublet nature of the :245-keV Y-ray peak and the existence of a 507.6-keV y. These data were essential to the construction of a correct decay scheme, and the two groups arrived at almost identical decay schemes containing the first five excited states in 62Cu that are populated by 62Zn decay. The most precise half-life determination for 62Zn, 9.2i0.l h, is also the work of Antman et a1. Bakhru (Ba68) also performed high-resolution Ge(Li) Y-ray spectroscopy, including coincidence experiments, and he measured the half-life of the 42-keV state to be 2.5t0.1 nsec. His decay scheme, however, differs in several placements from the others. The most recent paper on 62Zn decay, by Hoffman and Sarantites (H069), again includes results from Y-Y coincidence experiments and shows a decay scheme almost identical to those of An67 and R067. Nuclear reaction and in-beam studies have been reported, also. Davidson et al. (Da70) have used the 62Ni(p,nY) reaction to study the decay of the excited states in 62Cu. They performed Y-ray angular corre- lations in addition to Y-ray singles measurements at various excitation energies in order to learn something about spins and parities as well as placements of the states. Fanger et al. (Fa70) report on similar 119 techniques using the 61Ni(n,Y) reaction to study states in 62Ni. The points yet to be clarified are clear: 1) None of the groups studying 62Zn decay was able to detect any Y rays with energies above 637 keV, although QE is 21620 keV. Part of this problem came from the inter- ference of Y rays from 62Cu itself, which quickly grows into the sources. But now that the decay of 62Cu is known (Jo69, Va70, Fa70) with some assurance, weak Y rays from 62Zn can perhaps be distinguished more readily. Also, the larger Ge(Li) detectors now available, having very good peak-to- Compton ratios, should allow one to detect very weak higher-energy Y rays. 2) Very little in the way of interpretation of the structures of the 62Cu states has been done. Both sides of the problem have been attacked with the following results. 1) Six new weak Y-rays that deexcite four new excited states in 620u can be reported. 2) The structures of the 62Cu states have been examined in terms of shell model states and the trends observed in this nuclear region, and this very straightforward method has been found to explain much of what is observed. 6.2. Source Preparation The 62Zn sources were prepared by irradiating natural Cu foils (69.17% 63Cu, 30.83% 65Cu) with 25-MeV protons accelerated by the MSU Sector-Focused Cyclotron. The reaction of interest was 63Cu(p,2n)622n. Typically, z150-mg targets were bombarded with a l-uA beam for 30—45 min. The only Zn contaminant of any consequence was 38-min 63Zn, which was essentially eliminated by waiting 4 hours before counting the 62Zn sources. All other possible contaminants were removed using the chemical separation described in Section 2.3. 120 6.3. y-Ray Spectra Many Y-ray spectra were taken over a long period of time, always using the largest Ge(Li) detectors at our disposal. Spectra were taken with the 2.5% and 3.6% efficient detectors, although most of the spectra were taken with the 10.4% efficient Ge(Li) detector. A typical spectrum taken with the 10.4% efficient detector is shown in Figure 40. As it was mandatory that the higher-energy portion of the spectra be optimized yet maintain a high counting rate in order to minimize stray background peaks that could mask the weak 62Zn peaks, the spectra were taken through a set of absorbers and with the geometry shown in Figure 41. Each sample was counted for several consecutive 6-h periods to insure that the peaks observed came indeed from 622n decay. In addition to the normal procedures, however, an on-the-spot efficiency calibration with 110mAg and a background count of at least 12 h were performed for each sample. A spectrum obtained in 6 h with the 10.4% detector using the absorbers is shown in Figure 42. Note that six very weak higher- energy Y rays attributed to 622n decay can be seen in this spectrum. The centroids and areas of the photopeaks were determined by using the computer program SAMPO. The secondary energy calibration was performed using the stronger peaks of 62Zn, its 62Cu daughter, and the ”0K present in the natural background. The efficiency calibration for the spectra obtained both with and without the absorbers was performed using the method described in Section 2.1.3. The energies and relative intensities of the 622n Y rays are listed in Table 8, where they are compared with the results of the other investigations that used Ge(Li) detectors. Since the point of the investigation was specifically to obtain new information about weak transitions, no coincidence experiments 121 0%,.)91'0917! ~-—. .. . 6621:: -~. (033)9229 C NN ma, mun «- (0 “8.19170le ("339)I‘GZZIIH (“Z ”)vgl ”9 ° HQ (ulagz'ess- ' 30730 9'96 Niagvue. ("33, wars—- ”#88 (0)18) Zb€8 - £9299 ..-. 999x._--.--n--,, ('BpngDSJI Mamas] :vst-_i-- ---” -.,-:.-.-M Kflfiulr-h. . ”a! 97-09 ‘ sowx-w . i__ ‘7 8 exam . ' ,, a - "" ""-' n . _.~- «g 0090: ‘ 91m A.‘ _‘_ “. -.- i , '\7 g ' 09092 .. . --.. some vase -..—... q .9 ,9 ‘9 IMWO 33a smnoo O f— T fl T y 18 s 902173 -~— ‘1' § 99193 —n::‘“, ‘H'f‘ 1 L- -- L_.-_.-: _. 11.-. _l§ 6'0 8 9 9 (D w v b 2 . . iamvuo 83d smnoo cOl 1 l L 1 {D m Q Q Q o no WBNNVHC) 83d SlNflOC) 3500 2500 CHANNEL NUMBER A typical Y-ray spectrum of 622m taken without absorbers. l500 l000 500 The Fig. 40. insets show the regions at 245 keV and 511 keV in greater detail. 122 |.90 cm Be 1 0.94 cm ' rophite SAMPLE L 0.32291 Al 1"— 0.94 cm Graphite l.90 cm Be IZJcm Ge (Li) g" detector 3 (true 2 coaxial) Fig. 41. A diagram of the sample and absorber placement used to study 622n decay. 123 I 3500 ()1 29109b| ”...! .13} 663V|~ ZEBEIqu )- —-4 :0 808a.. C: N N m (humerus-m . . o I' (no Hagen-H) 8 ' u----‘ a (U2 2359mm ’5 N 99 ~ (9)6)9.€90| -} "(pus 7 9'9l6 J§ (now) valet-191.3- N (9M8)Z't7€8 NUMBER A typical 6-h Y-ray spectrum of 622m decay taken using the absorbers as shown in Figure 41. r 1 l500 (9)48)Z'l99 992:9 / 99969 -— -- .. . ..————,_-_._--, 7, Iv'gpg... . ..../ NTH§'*'° CHANNEL I 1 |000 O )- do l0 (\1 asvsm >4 A>asvsm ANoHava»m A>axvsm sh Asaxv m An Asasvsm Aooomv mmuaucmumm Awommv Ammomv czoum mam Anoq 7.0 __ .1...- “L 4 243.44 (< 0.2 x) (> 7.0) E! I, e . iY . -- ., .- y . _ ----,{/40.94 (~O) ~ -_. - - 0 4) 343%6 9| ’ 4. 62C” I ,%3)9 29 33 Fig. 43. 62Zn decay scheme. 126 were performed. A decay scheme which includes the present work is shown in Figure 43. The levels, spins and parities, and transition placements below 950 keV are from Davidson et a1. (Da70), which are consistent with the other results, and the energy levels above 950 keV are from the 61Ni(T,d) reaction (M067). The percent feedings were determined from the percent ground state feeding determined by Hoffman et a1. (H069) and the relative y—ray intensities and are found on the right of the decay scheme. The log ft's based on these feedings are on the extreme right. 6.4. Discussion 29Cu§§ is an odd—odd nucleus one proton and five neutrons removed from the doubly closed shell at Z=N=28. The simplest approach is to extend the the odd-group model, as normally applied to odd— even and even-odd nuclei. In this model the properties of the nuclear states are assumed to be determined primarily by the odd group of particles. In extending it to odd-odd nuclei it is assumed that the wave functions for the states and the odd-odd nuclei are simple vector-coupled product of wavefunctions of the two odd groups. If it is assumed that the residual p-n interactions are weak compared with spin orbit forces (De61) jj coupling can be used with its simp- lifications. With the assumption of jj coupling, a given proton and neutron configuration I2 j l jn ;>, can take on all integral spins, P P n ij-jnliIijp+jn, where the nature of the residual p-n interaction will determine the ordering of these spins. The modified Nordheim coupling rules proposed by Brennan and Bernstein (Br60) can be useful in predicting the ordering of the spins resulting from a given 127 configuration. Here jp and jn are the single-particle total angular momenta obtained from the adjacent odd-mass nuclei, while 2p and Zn (assumed to be pure) are the orbital angular momenta obtained from the standard shell model assignments. Examining the systematics of the odd mass Cu isotopes, Figure 39, and the odd mass N=33 nuclei, Figure 44, the 62Cu ground state is assumed to be a (Wp3/2)(gp3/2)—1 configuration for which the coupling rules would predict a ground state of 2+ with a 1+ first excited state. However, it is found that these two states are reversed with the l+ being the ground state. If the ground state configuration were (flp3/2)(up1/2), the coupling rules would predict the states in correct order. It has been found (Ph68) that there is considerable configuration mixing between these two configurations as well as others which would explain these results. Table 9 gives the possible proton-neutron configurations in 62Cu and the spins they would produce in approximate order of increasing energy. The individual proton and neutron orbitals are given in order of increasing energy as determined by the odd mass Cu and odd mass N=33 nuclei. Although the proton orbitals remain well behaved, the neutron orbitals are closely spaced and can change ordering rather easily. As a result, the relative positioning of the levels in 620u is difficult to predict and considerable config- uration mixing can occur. Therefore, a further explanation of the higher-lying states of 62Cu will require more calculations on the orbitals as well as further experimental results. A comparison of the levels in 62Cu with those of other odd-odd Cu isotopes is shown in Figure 45. 128 .Aooamv aNmm ecu .Amsoov HzH6.Am6HeV mmmm aoum ma mumv one .Hmaosa mmua mo mowumamumxm .qq .mflm mm mm mm on mm mm mm mm mm P. _ my 00m wa .26 mmm oil he .3 -Na -N\m ooNl -~\n LN\: -N\_ -N\m nxvv.r. -mxn nxuw.| mmmww\_ -N\m «N\n 0001. -~\m AunxU_.u >9. 129 Table 9 States Produced by Some Low—Lying Configurations in Odd-Odd 62Cu. Proton Neutron States Orbital Orbital Produced + + + + np3/ vp3/ 2+,1+,3 ,0 2 2 l 2 Vpl/ +’ + + + Vf5/: 1 92 )3 94 + + “pl/2 Vp3/2 1+,0+ Vpllz 1+,2+ VfS/Z 3 ’2 “f5 VP3 4+.5+.3+,2+,1+.0+ /2 /2 + + Vpll 3+’2+ + + 2 1 ,2 ,3 ,4 130 OON .l 00v .l 0001. 08. I >mx .Aoeumv 90mm 6cm .Amomnv so as .Aommmv nose .Aonmnv sums .Awoowv zoom .mmmouomH so mmme am>m wsu mo moHumEmumxm .Anooov 50mm mum moocmumwmu one hm 0N :wa Ce L +N .nw .n .N 4v .m mm mm 30% L mm mm : 0N0 L .N .v .N rm. N. r3 .va _n mm 3 000 +N +— .mq .mHm mm mN 3 0mm +_ +0 CHAPTER VII DECAY OF 636a 7.1. Introduction The first report of the production of 63Ga occurred only recently, in 1965,by Nurmia and Pink (Nu65). It was discovered in their search for B-delayed 6 emission in the light Ga isotopes. However, the only information they reported was that it had a 33—sec half-life, and they estimated its decay energy at 5.3 MeV. Since then, a study of its decay scheme was reported by Dulfer et al. (Du70). Other studies of the excited states of 63Zn have been performed by charged particle reactions. Birstein and coworkers have reported results from 63Cu(p,ny) (B166) and 60Ni(a,ny) (B167) reactions and have reported the results of y-ray angular distribution experiments from these reactions (B168). Also reported have been other 63Cu(p,n) (BrSSa, An62, Mc66, Ta70), 6hZn(p,d) (Jo68), 6L‘Zn(d,7‘:) (Ze60), and 61+Zn(T,0L) (Be67, F067) results. A composite comparison of these results giving both R and ITI values with the present work is shown in Figure 46. The 63Cu(p,n) results have not been reported above 1440 keV. 7.2. Experimental Procedure The sources for the study of 63Ga decay were produced by irra- diating 6-mil and lO-mil thick natural Zn foils (6”Zn 48.89%, 662m 27.81%, 67Zn 4.11%, 68Zn 18.57%, 70Zn 0.62%) with 30-MeV protons from the Michigan State University Sector-Focused Cyclotron. This beam energy was chosen to maximize the production ratio of 636a to 6"(3a, the principle contam- inant. Figure 47 shows this ratio as a function of incident beam energy. The various energies were obtained by degrading either 40-Mev or 34-Mev 131 132 3.2 an ... 19.653 6.353 _ u\_ _ -\_ 9_ .. E e 363 mmumum vmuHUXm mzu mvsum ou pom: mCOfiuowmu msowum> ecu mo kumeeam < xmoz, hzwmwma IIIIIIUfl AkanV HHHHHHHH eknfis .kn. TBV .oq .map 1:0 .Im%N >05. on A 01 PRODUCTION RATIO 6360/6460 N 133 1A. 1 l 40 36 32 28 PROJ ECT ILE E NERGY (MeV,PROTONS) Fig. 47. Relative production of 630a to 6”Ca as a function of incident beam energy. 134 P13c>ton beams with the appropriate thickness A1 absorbers. A typical iIrradiation was a 1-2 second burst of an 30.5-uA proton beam. The tiargets were then moved quickly (:7 sec) from the irradiation area to £1 distant counting area by a pneumatic rabbit system (K070). The samples Veere counted with either the 4.6% efficient or 10.4% efficient Ge(Li) detector and using the Ge(Li)-time coincidence system described in Section 2.1.2.C. The time length of the ramp was varied from 120 to 1560 seconds, depending on the particular experiment. In the search for low energy y-rays, a Si(Li) x-ray detector was used in place of the Ge(Li) detector. Along with each Y-time coincidence experiment, a y—ray singles spectrum was obtained. A typical experiment involved adding together the spectra from as many as 250 Zn foils. An energy calibration of the stronger Y rays in the spectrum was performed by counting the Zn foils with 2l+1Am, 1F”Eu, and 192Ir as internal standards. Also used for the calibration were the Y rays from 63Zn and the l332—keV and l791-keV Y's of 60Cu which were internally present. Table lOlists those strong Y rays from sources other than 63Ga that were counted concurrently. These Y rays were then used as internal secondary standards to calibrate the weaker Y rays in the spectra. The intensity calibration was obtained from the procedure described in Section 2.1.3. The centroids and areas of the peaks were determined by the computer program SAMPO. 7.3. Experimental Results A typical y-ray spectrum is shown in Figure 48. Sixteen Y transitions were assigned to the 63Ga decay, and their energies and intensities are listed in Table 11 along with the decay scheme results of Dulfer et a1. (Du70) and the 63Cu(p,ny) results of Birstein et al. (3166). 135 Table 10 Measured Y-Ray Energies Isotope Energy 60Cu 826.05:O.15 909.32:o.15 1035.1220.20 6“ca 807.85t0.10 918.77:0.12 991.50i0.10 1387.35i0.10 650a 114.97:o.10 152.93:o.15 751.68:o.1o 932.05:o.15 1047.23:o.20 1354.22:o.2o 136 M09 6360 09,, 9I66 "as::) "990' 02,, {5| 29609 09,, 8‘8I6 fl 6 "so. 0 929 ‘29:}... 99 09,99'.91.09— *--"==‘ 0999 1. I9[“"""' uz,9 u. 699 ‘3 0' ‘29— |__099,':;— _ ILZQ .192. ’— ——o ...—h.-. . . n .-..3es__g;;v 8’682 09172.2) 09 0' 02 ()9'36 ‘ 09 99 EG'ZQI- 09991.66" -....." ‘I "3°” 92 091» \ uz ,9 $0 éfi2\ 9,421.99 09;,9 ”9‘2. .' mzr 17902; 000, 92°92“- - oz 9, vii—Sill 09 99 Z‘GEOI fl 0‘. I ... 9 991.-.. 97* l I‘966I ’ n00. 9'I99I-«}j 09 z u ' - 9"GL| AM" 1.. I69| ...-g.-. 09,, 2929 3’ 09,9 329'" 9 9'999I- S386bl 09’9 09 b ”29ng d—ngm 0117-" W90 99 zrvou af- 0 0.0.0... . ..+ IO4—. I 0 Q "IBNNVHD I “’9 83d 1 ”e SlNflOC) l500 2000 IOOO CHANNEL NUMBER 500 A typical y—ray spectrum from the decay of 636a. Fig. 48. Y-Ray 137 Table 11 Energies and Relative Intensities from the Decay of 63Ga Present Work Dulfer et al. Birstein et al. E f E(Du70) I E(Bi66) 193.0i0.2 51.4i3.5 l92.9i0.2 49 190i2 248.0i0.2 30.6i2.0 247.8i0.2 32 246i2 389.8i0.7 3.4il.7 390 415.0il.3 2.6t1.5 412 457.9i0.6 5.4il.4 459 627.110.15 92.1:4.5 627.1i0.2 } 62732 637.0i0.15 =100. 637.1i0.2 =100. 636i2 650.1t0.15 44.0i2.5 649.9i0.2 44 649i2 768.5i0.2 19.0i2.3 768.2:0.5 l2 1054.6i0.9 2.3il.2 1065.2i0.4 l9.9i4.0 1065.1i0.6 18 106134 ll47.0i0.8 3.1i0.7 1203.4:2.0 2.4tl.2 1395.4i0.3 37.0i7.0 1395.5t0.5 41 1498.5i0.6 2.9i1.5 l69l.7:0.5 27.4i5.0 l691.8il.0 28 I 138 The uncertainties in the energies in Table 11 are based on the uncertain- ties in the energy standards, the height of the peaks above the back- ground, and the reproducibility of the calculated energies from the different spectra. The relative intensities listed are the average from several spectra and their uncertainties are based on the reproducibility of the intensities and the uncertainties in our experimentally determined efficiencies for the detectors. The errors are in general 50% greater than the largest deviation of a value from the average of several runs. There is quite good agreement between the present results and those of Dulfer et al. (Du70). Seven Y rays were observed in the present study that they did not observe. An upper limit of 2.5 in the units of Table 11 has been placed on the intensity of any unreported Y rays below 511 keV and a limit of 2.0 on those above 511 keV. A search for Y rays from 636a in the energy range 1700 — 4000 keV was performed, but none was observed. A similar search for Y rays below 100 keV was performed using the x—ray detector, but none was observed in this region either. A half—life of 32.4 i 0.5 sec was determined for 630a by using 12 spectra from the Y-time coincidence system to measure the half-life of the 193-, 627-, 637—, and 650-keV Y transitions. 7.4. Decay Scheme The decay scheme produced from the present results is shown in Figure 49. Transition and excited state energies are given in keV with the adOpted energies for the states being a weighted average of several experimental runs. The Q8 of :5.6 MeV was obtained from the mass table of Garvey et a1. (Ga69). The total transition intensities, in percent of total 63Ga decay, are given in the decay scheme. Since all of the inter- nal conversion coefficients would be less than 1% of the individual Y 139 l69l 7 (3 08) |498.5(O.33) |054 6(0 26) 5/2- I§9I,7 3.67% 5.7 §E§§ SQQN V c I?» 70' S :3- m 0 v w 3/2-,gI/2-) '2 ‘l‘ = r~ 895.4 6.9I% 5.6 3 1 N. m 9’) N N 9 .n' o w 9 (3/2-I 9 v I065.2 2.53% 6.2 96393 +6599 1: F: O. (D —. 8.535833 650I 5.26% 6| v2-(3/2-Ig—‘L—3/2- _‘° v ‘0 ”=0 ' H.377 5.7 n (W ——‘ 8.22% 5.9 2? V. a s O . 3' 1‘2 I/2- N ,9, 2.7|% 6.5 5/2- ‘1’ 83.0 4.58% 6.3 3/2— I o 54.8% 5.3 38.4 min 632” 30 33 Fig. 49. Proposed decay scheme of 63Ga. 140 intensities, they were ignored. Using the ratio of the 511-keV Y to the 627-637-650-keV y-ray triplet measured by Dulfer et al. (Du70), with which these results are consistent, and the theoretical e/B+ ratios for the levels (Le66), the total relative feedings to each state were calculated. These total feedings are given in the decay scheme to the right of the energy levels. The log ft values based on them appear at the extreme right of the levels. The spin and parity assignments discussed in the next section are on the left of the levels. A comparison of these results with those of charged particle reactions was shown in Figure 46. 7.5. Spin and Parity Assignments Ground State The ground state of 63Zn is assigned Ifl=3/2- on the basis of charged particle scattering experiments and decay scheme systematics from its decay to states in 63Cu (cf. Section 5.5.). From scattering reactions an £=l transfer is indicated, limiting this state to 1/2— or 3/2-. It has an allowed 8 decay to the 3/2- ground state, 1/2— first excited state, and 5/2— second excited state in 63Cu, thus limiting the assignment to 3/2-. The log ft of 5.3 indicated an allowed 8 decay from the 63Ga. 193.0—keV State Scattering results suggest an assignment of 5/2_. The y—ray directional correlation experiments of Birstein et al. (Bi68) indicate the 193—keV y to be a 5/2- to 3/2- transition. The log ft of 6.3 indicates an allowed transition from the 63Ga and supports the assignment. 248.0-keV State The log ft of 6.5 suggests probably allowed 8 decay which would limit the assignment to l/2-, 3/2-, or 5/2-. This state decays solely to the ground state. Although the 63Cu(p,n) results report this level, none 141 of the other charged particle experiments observed it. Examining the systematics of the odd-mass Zn isotopes as shown in Figure 50 and the systematics of the N=33 isotopes shown in Figure 45, a 1/2- level in the region below 400 keV is strongly suggested. Since this is the only level that could fit these systematics, it is therefore assigned I"=l/2-. The ground state of 63Ga is assigned Ifl-3/2- since allowed 8 transitions are observed to the 3/2- ground state, the 5/2— first excited state, and the 1/2_ second excited state in its 63Zn daughter. This assignment is consistent with the systematics of the light odd—mass Ga isotopes and the shell model (the odd proton being in the 2p3/2 orbital). 627.1—, 637.0-, 650.1-keV States The 8 feeding to these states has log f%'s of 5.9, 5.7, and 6.1, respectively, all allowed transitions. Results from all the scattering experiments indicate i=1 transfers, most likely 3/2- states. The proba- bility of i=3 transfer was considered small. The 627-keV state decays solely to the ground state, while the 637-keV state also decays to the 248-keV state and the 650-keV state also decays to the 193-keV state. The 627-keV state is therefore assigned I"=(l/2-, 3/2-), the 637-keV state I"=1/2‘, (3/2‘), and the 650-keV state I"=(3/2‘). 1065.2-keV State This state has a B feeding with a log ft of 6.2 and decays to the ground state and the 650-keV state. Results from 63Cu(p,n) also indicate a level at 1028 keV. Scattering results indicate both i=1 and £=3 transfers in this region for presumably a doublet with i=1, In=3/2- dominant. This state is therefore assigned Ifl-3/2-. 1395.4-keV State This state has more 7 branching than any other state in 63Ga. 142 It decays to the ground state (3/2-), the l93—keV state (5/2-), the 248- keV state (1/2-) and the 627-keV state ((1/2-, 3/2-). It also is populated by an allowed 8 transition, as indicated by a log ft of 5.6. The 61+Zn(p,d) results suggest a 3/2- state in this region. The 63Cu(p,n) results indicate two states here, with the 1395-keV state the closer to the state observed in the (p,d) results. An ITr assignment of 3/2_, (1/2—) is suggested for this state. 1691.7-keV State This state decays to the l93-keV state (5/2—) and the 637—keV state (1/2-, (3/2-)) in addition to the ground state. The log ft of 5.7 for feeding to this state indicates an allowed decay. The results from charged particle scattering suggest an i=3, Ifl=7/2— state. Since a 7/2— assignment would not permit allowed 8 decay, this state is assigned In=5/2-, which is consistent with all results. 7.6. Discussion The 63Zn is in the region above the doubly closed shell occurring at 56Ni. In this region the active particle states for both neutrons and protons are the 2p3/2, 2p1/2, lfS/p’ and lg9/2. Since both 199/? orbitals are well above 2 MeV (cf. Figures 39 and 50), they will be ignored. The odd nucleon in 632m is a neutron found in the 2p3/20rbital. In contrast to its 63Cu daughter where the low-lying states are from the odd proton coupling to a core vibrational state, the first two excited states in 63Zn appear to be primarily single particle states, the first being the ifs/2 and the second the 2p1/2. These three single particle states remain rather closely spaced in the lighter Zn isotopes with the 1f5/2 being the ground state for 652n and 67Zn. The triplet of the 627-, 637-, and 650—keV states appear to be 143 _¢c on N:. ..\_ oxm .Bfln in. ..\_ -xn 1 {n in 1| {min A): «$6 .noo> Eopm ummu wnu was .92 Eoum swam .xp03 ucmmmum mcu Eoum mum muasmmu CNmo mLH .meOuomH cm mm On hm Om cNmm cNao -\_ in -2 in .\m .\m in .\m {min B {and -2 in 4&1. {n.(m o\_ {al. {m -\_ mmmalvwo mzu mo mofiumsmum%m on On an0 -\n -\_ -\n A); c\_ {m .\_ o\m {mum in.) +\_ anm Ti lads: A-\na-\_ The .-xmv Akmv 1.06 l O.— .| O.N >22 144 core coupled states. Since the log ft's to these states fall between that of the ground state decay and those to the first two excited states, these states would therefore result from the coupling of the odd neutron in the 2p3/2 orbital to a 622n core excitation. However, since little is known about the excited states in 62Zn, the details of these states must be left to a later time. Not enough is known about the higher—lying states in 63Zn since they occur above the pairing gap and could result from several different sources, so therefore little can be said about them here. The B decay from 63Ga to the states in 63Zn presents some very interesting problems. The ground state of 63Ga apparently has the odd proton in the 1Tp3/2 orbital. The ground state of 63Zn appears to be (H p3/2)2(vf5/2)2(vp3/2)3 or some similar neutron configuration since it has five neutrons outside a closed shell and an Ifl=3/2-. While a neutron configuration of (vp1/2)2(vp3/2)3 might appear to more easily explain the ground state of 632m and the nonobservance of its 248-keV (l/2-) state in all the scattering reactions, it is not a probable configuration since it would require the lower spin state of an Q to be below the higher spin state, and this does not occur in nuclear level systematics. The more probable configuration suggests that the VPx/y and vfg/Zstates are degenerate so that both may be partially filled. The decay from the 63Ga indicates a normal allowed transition to the 63Zn ground state with its suggested degeneracy, while unexpectedly slow 8 transitions feed the supposedly pure single particle 5/27 and 1/2- states. A much more detailed study of this region is necessary before these states in 63Zn can be fully explained. CHAPTER VIII 620a AND B-DELAYED a EMISSION 8.1. Introduction The occurance of B-delayed a emission has been known for a long time. In 1935, Crane et al. (Cr35) reported the B-delayed a decay of 850-msec 8L1. Alvarez (A150) in 1950 expanded the list when he reported similar decays for 774-msec 8B, 11.0—msec 12N, and 405-msec 20Na. Further searches for B-delayed a emission in the light elements have produced 20.4-msec 12B, 7.13-sec 16N, 2.09-sec Zqu, and 297-msec 32Cl. All of these nuclei are of the type N=Zt2, where Z is odd, 8 decaying to excited states in N=Z even-even nuclei. The excited states immediately decay by emitting an a particle rather than by the usual Y emission. In their report of the discovery of 33-sec 6363, Nurmia and Fink (Nu65) reported their purpose was to look for delayed o's from 626a, but they did not observe any. Their search was based on calculations by Taagepera and Nurmia (Ta6l) which indicated the possibility of B—delayed a emission in the nuclei just above the 56Ni doubly closed shell, among other places. Fengés and Rupp (Fe68) used these calculations and the Myers and Swiatecki mass tables (My65) to predict the onset of B—delayed a and proton emission for all elements through N=84. Their results indi- cate that 61+Ga would be the heaviest possible B-delayed a emitter for Ca, with delayed proton emission expected to start with 62Ca and direct proton emission expected to start with 606a. Figure 51 shows the mass equation-based predictions of Myers and Swiatecki (My65) for the light Ga isotopes as well as predictions based on experimental results from the 63Ga decay described in Chapter 7. The figure indicates a and proton binding energies from both sources. Since 145 146 .m Hmuamco scum muasmmu >m91> osu mum vmwzaocw oma< .Qz Eoum mum Anv cmamnma mmozu com mesa scum mum Amy mum-4 Own a 0.3.2 Sfl 00".” -fifiu 0.8 £3 a. Q n. 20 mum K3 8 BB 5 :8 nmfimnms qud and nrO. omens .meOuomH :N unwwa Mow mmflmumcm wcflvafln a cam Cououm .Hm .mHm 6.4 om.q .d 8.5 0 we“ ..." 1w , Wm“ 8.0 J?! ‘3 .8 ”N [04 0.9.5. .FN an. 0.3., 13.-...... '9. .3 ONE rum a. ““6 6n 3. {u .ags 39.3.6 «5 1% Jon, 3. :8 tn. 147 the proton binding energies are close to those for a particles, the lower Coulomb barrier could make B—delayed proton emission competitive with the B-delayed a emission. The general trend of increasing decay energy with decreasing particle binding energy is easily seen both in calculated and experimentally based binding energies. An anomaly is seen in the binding energies of 606a. The B-delayed a emission of 6063 would lead to 56Ni, a doubly closed shell nucleus. However, the experimentally based binding energy is larger than that of 61Zn, and the proton binding energy is the same as that for 612n. The corresponding calculated values from Myers and Swiatecki (My65) decrease approximately with A. With these results and calculations in mind, a search for B-delayed a emission in the light Ga isotopes was begun. 8.2. Experimental Procedure The search for B-delayed a emission utilized the He—jet thermal- izer and a detectors described in Section 2.2. In addition to the a detector, the 4.6% efficient Ge(Li) detector was also used to count the y rays from the collected nuclei. The targets used were 0.1—mil thick natural Cu foils. Three foils were used at any one time, each separated by a 0.8 inch thick teflon block with a l-inch 0 hole in it. An incident beam of 70 MeV T of about 0.4 uA current was used to produce the light Ga isotopes. Lower beam energies were obtained by degrading the beam with Al absorbers. The range of the recoils produced with this beam is 0.035 mil in Cu or 0.74 inches in the 2 atm He used. The ranges were calculated using the results reported by Harvey (Ha60). The recoils were collected on masking tape. The bombardment energies of 70, 55, and 40 MeV were Chosen to represent the peak in the production cross section of 61Ga, 626a, and 636a, respectively. 5 m COUNT§ PER CHANNEL 0— 148 . I F“ 20 a 8 No . : N i 4 a, s .. :0 "2 <1? " . fl " ’E‘ _< - .. <1- ... 0' NV 1 ('1' ([3 J ‘3 -' ‘ N " to ID "- : ‘ ' 3. ‘ 0°. «5 = .1 ' [0 <1- [- 1- 2'1 ". .. 1‘ : u- :7»... «L. If - rd 1 .- --...- ... .. .. .. ...... .. r -J . ___, l . __ v 0 500 IOOO CHANNEL NUMBER Fig. 52. An a spectrum from the B-delayed o emission of 20Na (P067). 149 In order to insure B-delayed a's could be observed, the B-delayed a decay of 20Na (P067) was examined. For this experiment, the Cu foils were removed and Ne gas was allowed to leak into the target chamber along with the He thermalizer gas. The results of this test are shown in Figure 52. In addition to the 20Na peaks, there is a peak from 2l+1Am. This appears to be contamination on the detector face and is seen in other spectra including those with no source present. For this experiment, the recoils were collected on a cooled Al block. 8.3. Results In Figure 53, the results of the search for B-delayed a emission in the light Ga isotopes are shown. Incident beams of 70—, 55-, and 40— MeV T were used to bombard the Cu targets, and the results from each beam energy are shown. The only peak observed in all three spectra is the 5.545-MeV a peak from the 241Am contamination on the detector. Only in the 70-MeV spectrum is there any sign of 6 activity. Four single channels in the region from channel 500 to channel 1000 have more than one count in them. The peak at about channel 550 has about 4 counts and the one at 905 has 3 counts, whereas the other two have only the two counts in the one channel. No counts were observed at these locations in other a spectra. The y-ray spectra corresponding to the o spectra shown in Figure 53 are shown in Figures 54, 55, and 56. Several isotopes appear here that were not observed in the 63Ga studies. In general, the shorter lived species will not be observed since the collection tape was changed hourly and therefore allowed a buildup of the long lived species. Examining the spectra, the 660a is found to increase by about one third going from 40 MeV T to 55 MeV T and increased by about one half COUNTS PER CHANNEL 150 70 MeV r l '24Am 55 MeV r 24! = Am J 40 MeV 7 24! ' Am CHANNEL Fig. 53. A search for B-delayed IOOO NUMBER I500 6 emission in light Ga isotopes. 2000 151 r I T l 1' ."i 'T .. . wi:| ! 45%.; . Hi}; -'qf:I9 " ..'il. "% riflfifi 09.. 8995‘s “"“w—fligi : r- 03” du';!55' b 'IEII Q, '- Q- :3 (J L. "309 men n 309 "0 man—:— 1 :9 “0309 ziw 099”"309 .. 0 _fl! ma P—t '1" ' ' ""i~ ..1 1.; . A . v n N _ 9 9 ° 9 9 WBNNVHO sad SlNhoo 2000 2500 3000 3500 4000 CHANNEL NUMBER y—ray spectrum from the recoils produced from bombarding Cu with 40 MeV T. l500 IOOO 500 Fig. 54. 152 .9 "’9 Q 'BNNVHO 83d SanOO uf': ' T ---| I f ' xsflgi 3 :' l' I i 9 1'4‘- .. .l. I - ' "!' .|: i ! 0:) T1; .!2 E . 09 ——-I ‘::|;:;§E. 2 09.90999: -~ ' ’ ‘ "Zilwi ,. '. o g _. b WW"- “5'53"? "3 ' — -213)!.:. > """3 511-II- ” njogl'baiifi " 1‘3 12f: \ "': 3 -:..".\ a o .0 at 0 five __ + “‘3'"‘-‘s.3~3- 3 .3. 0 Mn "fl?“ -. - C u . i399 "0m ,‘. 4&5 .w - 09 ' . 33.. ":13 0309 ’ __ "309 "‘ 6 n ._..-*hls‘ ”"79 at 0N "am as am “‘7’” w, ' .‘ "39. 0590293" '13-- 0'.) 00:) 99 09 "9» —" i. ”l‘¢‘ 896 T '.i.':j*-- _ n -' “was canes—‘1 ”WeaQEEEE 0999 999 ”was ' UZgg ”699 "3'9 ' "2299969 Ions . _ -5963???“- "3'9 "3'9 6'38? 0%9 09" J. ~10 Io'oooofiliooul. no - l ‘1 A no N 4000 2000 2500 3000 3500 CHANNEL NUMBER ISOO IOOO 500 T. y-ray spectrum from the recoils produced by bombarding Cu with 55 MeV Fig. 55. 153 4000 [7 r l . ' 0:) .._. 4" 09 .;.‘ - I —N) , " O o - 8 r. "#7 IN) 0 .1; 3 . ~15 C) .md .51.: 025:1: E3 _ . . -‘ l0 .. .3 ngmw-Bfiz; .... rd" .4W‘ «Z.9 ' r009 __fl 0 m no... ,. g m b "3 "‘ ‘3‘; d N CD 0 no men - 9.”:“7 2 °° ”‘5 g 3 stf 2 L .J )4”. DJ _ “"2; uz‘éf— " _. § 2 m5 __2: "3 E'ZEEI --- g3 ‘ r - ~‘ 4 69 n1)— ngs , °%§ 3 “3'9 0 .n 0999 k) 0 uztgw‘zss n . _ O 0:) "D “"59 09' 99 uz trees {33" ...:1?‘ ”289 "2°27, tom aunt» _ ,_ ,..... é) _ —1 "3,9 628?. -- “a l --r-a.- . O-o.l.-...u.g--;Al l l 0 £0 an IO 9 ‘79 9 N9. ‘IBNNVHO 83d SLNHOO y-ray spectrum from the recoils produced by bombarding Cu with 70 MeV T. Fig. 56. 154 again going to 70 MeV T. The 650a in turn decreased by about 40% from 40 MeV to 55 MeV, and decreased slightly further going to 70 MeV. Both of these isotopes are only weakly seen above 40 MeV and are hard to measure accurately because the 660a is obscured by stronger nearby Y rays from other isotopes present and the 65Ga is overwhelmed by the underlying Compton background. An increase by a factor of 2.7 is noted in the 61+Ga intensity going from 40 to 55 MeV. The increase was reduced to only a factor of 2 for 70 MeV as compared to 40 MeV. The 63Zn daughter of 63Ga increases by about one fifth from 40 to 55 MeV and increases by another half at 70 MeV, while the “QZn daughter of 626a increases by one half at 55 MeV then drops to only about five sixths at 70 MeV. A doubling of intensity from 40 MeV to 55 MeV is noted for 61Cu, with an additional increase of one half going to 70 MeV. 61 Zn is observed only weakly in the Compton valley from the 511—keV Y but does appear to have the same intensity relations as its more obvious 61Cu daughter. The 60Cu, in turn, has about the same intensity at the two lower energies, but an intensity at 70 MeV of more than 4 times that at lower energies. Some of the peaks present result from beam interactions with the Havar foil separating the evacuated beam line and the pressurized target chamber, the Al collimator and absorbers, and the natural background. Some isotopes occuring from these sources are 56Co, 52Mn, Sth, and tha. In addition to the Y rays from these isotopes, several other Y rays, mostly weak, were observed but could not be identified, although their source is believed to be reactions with the Havar foil. Figures 57 and 58 show the calculated cross sections for 63Cu and 65Cu produced by the program CS8N written by T. Sikkeland and D. Lebeck 155 q 10 BN 2N HN 5N ..06‘.““‘.“.““““r 3 ". \ «mo , ' Z 0: 1N CE m 9 h—d _J .J ...—4 Z 102. Z 5.... Z O ... 8N '— (.J L” 1 c010 ,. U7 0') C) O: C.) 0 10 0 110 20 \ '3! 410 50 60 70 L98 t~tébv IN HEV Fig. 57. The 63Cu(r,xn) cross sections calculated by the program CS8N. 156 10" F 3N HN SN 2N ‘...“...¢.¢oo¢o¢¢ou 3 ~". 0710 - .' Z O 0: SN Ct CD . t—g .5 .J ha 1: z: 102 , :2 F H 2: ca L—q ..— (J ”J 1 0310 _ f a) . 05 D 0: LJ 0 .'- 10 . . . . l o 10 0 to 70 Fig. 58. 20 ' LsB tNEflhv INOMEVS The 65Cu(r,xn) cross sections calculated by the program CS8N. 157 at the University of California, Berkeley, to calculate the results of bombarding heavy elements with heavy ions. The relative cross sections predicted by the curves are in general agreement with the experimental results, taking into account that the interacting beam degraded by the Al absorbers, is not monoenergetic like the incident beam, but has a large range of energies, the range being larger for the thicker absorbers. It should be said that the isotopes of masses 61 and heavier are con- sidered to be daughters of the Ga isotopes produced by the Cu(T,xn) reaction. The 60Cu and lighter masses are primarily from the Cu(r,0xn) reactions. Since 61Cu and 61Zn are observed as well as 622n and 63Zn, it appears that the light Ga isotopes, 610a, 620a, and 63G3, have been produced. Since the 60Cu is present from other reactions and the pre- sence of 6oZn cannot be determined because its most intense Y rays fall at the same energy as much stronger transitions in the spectra, the production of 600a is hard to evaluate. However, the large increase in the 60Cu intensity from the 70-MeV T beam gives a strong indication that 606a was produced with this beam. These isotopes were not observed directly since their half-lives are expected to be seconds or less. However, based on the intensity of the daughter decays and the lack of observed 0 transitions, an upper limit of about ten parts per million can be placed on the B—delayed a branching of any of these isotopes. This could be due to the Coulomb barrier of the nuclei or the lack of B feeding to states above the a binding energy. CHAPTER IX CONCLUSIONS Although there has been comparitively little work done on it, the region beyond the doubly closed shell at S6Ni can provide significant information about the structure of the nucleus. Since 56Ni is not stable and 58Ni is the lightest stable nucleus in this region, the nuclei just outside the doubly closed shell are not as easily produced as those near the lighter doubly magic nuclei. To add to the difficulty in studying these nuclei, their half-lives are short, minutes or less, making decay scheme studies rather arduous. One of the purposes of examining this region is the possibility of B-delayed 0 emission occuring in the light Ga isotopes. An extensive search for this 0 emission was conducted by producing isotopes as light as 600a. Although some hints of delayed 0 emission were observed, the only definite result was the placing of an upper limit on the B—delayed 0 emission in this region. Excited states in several other isotopes have also been studied in order to learn more about the systematics in this region. In the investigation of the B decay of 63Zn a new level and several new Y tran- sitions were observed. The new level is one of the doublet of the 1861- and the 1865-keV states. All previous studies of the excited states in 63Cu report only a single state at 31863 keV. Several different coinci dence experiments were also performed to help elucidate features of the 63Zn decay scheme such as the differences in eK/8+ between the strongly collective states and the primarily single-particle states, all supposedly fed by allowed 8 transitions. An examination of the decay scheme of 62Zn revealed six new Y 158 159 transitions, one of which had been previously observed only in 62Ni(p,nY) reactions. Since 62Cu is an odd-odd nucleus, the structure of its states is much more complex than other nuclei and requires considerable under- standing in order to interpret it. Seven new transitions were observed in the B decay of 63Ga. No transition from this decay was observed above 1700 keV. Since the a binding energy, and therefore the lower energy limit on B-delayed 0 emission, lies somewhere in the range 1700 to 3300 keV depending on the mass tables used, Y transitions in this region would greatly aid in placing a firmer limit on the a binding energy and the possibility of B-delayed 0 emission. Although the results reported here produce some new insights into the systematics of this region just above the doubly closed shell at 56Ni, more information is needed before a good understanding of the behavior of the nuclei in this region can be obtained. More results, both experimental and theoretical, must be obtained before a consistent interpretation of the energy levels in these nuclei can be presented. The results presented here represent but a small step on the long road to this end. 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