HIGH RESOLUTEOLN GAMMA RAY SPECTRAL SIUDJES OF THE DECAYS OF 1171.8, lngTe'IIQm T9, 129gTe’ ANDIZQmTB Thesis for the Degree of Ph. D. MICHEGKN STATE UNWERSITY GEORGE 1,. BERZENS 1957 LIBRARY hdfidbq§mn15cana [Juivcxsflarr 1H ems This is to certify that the thesis entitled High Resolution Gamma Ray Spectral Studies of the Decays of 117 II9gTell9mTe 1299 AND Izgfife ’ Te’ presented by I George J. Berzins has been accepted towards fulfillment of the requirements for _EIL_D__ degree in M :3 ~ H w « Major profes/or Date Jove L1; [367 0-169 DEC 0 32-005 ABSTRACT HIGH RESOLUTION GAMMA RAY SPECTRAL STUDIES OF THE DECAYS OF 117Te, 119gTe, 119mTe, 129gTe AND 129mTe by George J. Berzins The energy states populated through beta decay have been investigated for the isotopes 117Sb, 119Sb, 129 and I in an effort to obtain information about energy level systematics in this region of the periodic table. Ge(Li) singles and Ge(Li)-NaI(Tl) coincidence spectrometers were used to identify many new gamma transitions which could not be distinguished in previous scintillation studies. Coincidence data, energy sums and relative intensity considerations were used to construct decay schemes for 117Te, 119gTe, llnge, 129gTe and 129mTe. In most cases significant changes in previous Schemes were necessary to accommodate all of the new transitions and to be consistent with all of the coincidence data. Excited states accommodating 18 gamma rays have been placed at 719.8, 923.9, 1354.9, 1u5u.8, 1716.5, 1810.6, 119 2213, 2285, and 2300.0 keV in 117Sh. Levels in Sb at 6uu.1, 699.6, 1328, 1338.7, lul2.8, 1u87, 17u9.1 and 1820 keV are populated by the decay of 16h 119gTe, while the 119m decay of H.6d Te populates levels at 270.3, lOU8.1, 1212.6, l2u9, 1365.8, lu07, 2129, 2226, 2278, 2283, and George J. Berzins 2360 keV. These two sets accommodate 12 and 20 transitions, respectively. The 32 gamma rays observed in the decay of 33d 129m Te in equilibrium with 70m 129gTe depopulate excited states at 27.7, 278.5, “87.6, 560, 696.0, 729.6, 769, 830, 8uu.5, 10u9.9, 1111.u, 1261, 1291, and 1u02 keV. Of this set, only the 696.0, 729.6, 8AM.5, 10u9.9 and 1402 keV states are populated by direct beta decay of 129m Te, while the 769 keV state is populated from both isomers. Unique spin assignments have been made to some levels in these isotopes, while limits on possible spins have been placed on most of the remaining states from log ft values and from the existence of transitions to levels of known Spins and parities. Angular correlation experi— ments were performed with Ge(Li) and NaI(Tl) detectors to obtain bases for some of the unique Spin assignments in the decay of 119gTe. Comparisons of the low lying energy states in several of the adjoining odd mass antimony and iodine isotopes Show systematic behaviors for a number of the low levels. Insofar as is possible, comparisons have been made with the predictions of some of the existing nuclear models. HIGH RESOLUTION GAMMA RAY SPECTRAL STUDIES OF THE DECAYS OF 117Te, 119gTe, llnge, 129gTe AND 129mTe By‘ George Jleerzins A TH ES IS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Physics 1967 ACKNOWLEDGMENTS I wish to thank Dr. W. H. Kelly for suggesting this region of study. His guidance and patience during the course of these investigations are greatly appreciated. Dr. C. R. Gruhn spent many hours in realizing a solid state detector laboratory. Without Ge(Li) detectors, most of the experiments performed in this study would not have been possible. Dr. H. G. Blosser and Dr. W. P. Johnson assisted with the cyclotron irradiations of isotopes for this study. Dr. R. L. Auble, Dr. L. M. Beyer, Mr. R. C. Etherton, Mr. D. B. Beery, Mr. W. B. Chaffee and Mr. R. Hickey aided greatly with helpful discussions and with data acquisition. It was a pleasure to collaborate on two Joint publications with Dr. W. B. Walters, Dr. G. E. Gordon and Dr. G. Graeffe of MIT. Mr. L. Kull provided a stimulus for philosophical discussions which were a welcome change of pace from the lab- oratory. Although it has been proven that the setting for these discussions is conducive to great discoveries, it was our misfortune that the bubble chamber had already been invented. Miss T. Arnette and Mr. J. O. Kopf made many useful suggestions during my initial bouts with the computer. ii Mr. R. L. Dickenson and Mr. A. Kaye were very helpful with the acquisition of equipment and sources for this study. Dr. H. Griffin of the University of Michigan provided access to the Ford Nuclear Reactor. Mr. N. R. Mercer and his machine shop crew and Mr. W. Harder and Mr. F. E. Potts of the electronics shop supplied valuable assistance by building much of the physical apparatus for various experiments. Miss Jean Lowe and Miss Cathy McClure sacrificed much of their time to help with the typing of this thesis. Miss Lowe and Miss Wilma Sanders were helpful in preparing for publication various reports arising from this investigation. The National Science Foundation provided financial support for most of this investigation. Finally, I thank my wife Joyce for her patience and her moral and financial support during these past few long and trying years. iii TABLE OF CONTENTS ACKNOWLEDGMENTS LIST OF TABLES LIST OF FIGURES . . INTRODUCTION Chapter I. II. NUCLEAR MODELS i4FJH UJNFJ 1.3.1. 1.3.2. 1.“. Nucleon The Shell Model . . . . . The Collective Model . . Particle- Core Coupling Model . Weak Coupling . . . Strong Coupling . Correlations . . . EXPERIMENTAL APPARATUS AND METHODS AND SOURCE PREPARATION . . . . . 2.1. Ge(Li) Singles Spectrometers . 2 2 Ge(Li)-NaI(T1) Coincidence Spectro- Page ii - vii oviii . 18 25 3O 35 U0 AA “5 meters . . . . . . 2.2.1. Conventional Experiments . . 2.2.2. Experiments Utilizing a Split— ring NaI(T1) Annulus . . . 2.2.3. Angular Correlation Experiments . . . . 2.30 X-I'ay IDtenSitieS o o o o o o 2.A. Positron Endpoints . . . . . . 2.5. Data Analysis . . . . . . 2.5.1. Energy Measurements . . 2.5.2. Relative Intensity Measure- ments . . . . . . . . 2.5.3. Angular Correlation Measure- ments . . . . . . iv “9 Chapter Page III. EXPERIMENTAL RESULTS . . . . . . . . 55 3.1. Summary of Previous Studies of the Activities of the 117Te, 119Te and 129Te . . . . . . . . 55 3.2. Results of this Investigation . . . 61 3.2.1. Dggay Schemes of 129gTe and mTe O O O O O O 0 O 6 l 3.2.1.A. The Gamma Ray Singles Spectra . . . . 61 3.2.1.8. Gamma-Gamma Coinci- dence Studies . . 67 3.2.1.0. The Proposed Decay Schemes . . . 75 3.2.2. Decay Schemes of 119%Te and llnge o o o o o o e o 79 3.2.2.A. The Gamma Ray Singles Spectra . . 79 3.2.2.B. Gamma— Gamma Coinci- dence Studies . . 89 3.2.2.0. The Proposeerecay Schemes . . . . 9“ 3.2.2.D. Angular Correla- tion . . . . . 101 3.2.3. Decay Scheme of 117%Te . . 109 3.2.3.A. The Gamma Ray Singles Spectrum . . 109 3.2.3.B. Gamma- Gamma Coinci- dence Studies . . 113 3.2.3.0. Positron-Gamma Coincidence Studies 115 3.2.3.D. The Decay Scheme 118 3.2.3.B. The Search for 117mTe . . . . 122 IV. DISCUSSION OF RESULTS . . . . . . . 128 “.1. Comparison with Reaction Studies and Identifications of some Corresponding States . . . . . . 128 “.2. Comparison with the Core— —0oupling Model . . . . . . . . . . 137 Chapter A Page 1291 . . . . . 137 . . . . . . 1“2 “.2.l Levels in “.2.2. Levels in “.3 Comparison with Pairing and Quadruple Interaction Calculations . . . . . 1““ V. CONCLUSIONS . . . . . . . . . . . 1“8 BIBLIOGRAPHY o o o o o o o o o o o o o o 151 APPENDICES . . . . . . . . . . . . . . 157 vi LIST OF TABLES Table Page 1. Typical Calibration Data . . . . . . . . “6 2. Studies of the Decay of 129Te . . . . . . 56 3. Studies of the Levels in 1198b . . . . . . 57 “. Studies of the Levels in 117Sb . . . . . . 58 5. Gamma Rays Observed in the Decay of l29m+gTe . 66 6. Summary of Coincidence Results for l29m+gTe . 72 7. Energies and Relative Intensities of Gamma Rays Observed in the Decay of ll9mTe . . . . 86 8. Energies and Relative Intensities of Gamma Rays Observed in the Decay of 119gTe . . . . 87 9. llnge Gamma-Gamma Coincidence Relationships . 93 10. Summary of 119Te Gamma-Gamma Angular Correlation Data . . . . . . . . . . 10“ 11. Comparison of Multipolarities Assigned by Various Investigators . . . . . . . . . 106 12. Energies and Relative Intensities of Gamma Rays Observed in the Decay of ll7Te . . . . 112 13. 117Te Gamma—Gamma Coincidence Relationships . 115 1“. Exgerimentally Observed Energy States in O O O O O O O I O O O O 130 15. Experimentally Observed Energy States in O I O O O O I O O O O O O 131 16. Properties of Similar States in Odd Mass Antimony Isotopes . . . . . . . . . . 13“ 17. Properties of Similar States in Odd Mass Iodine Isotopes . . . . . . . . . . . 136 vii Figure 10. 11. 12. LIST OF FIGURES Page Examples of rotational and vibrational energy levels which are characteristic of even-even nuclei in the deformed and the spherical regions, respectively, of the periodic table . 1“ Relative photopeak efficiency curves for three Ge(Li) detectors . . . . . . . . 32 Cutaway view of the Ge(Li)-NaI(Tl) annulus coincidence spectrometer (from ref. 26) . . 3“ A schematic illustration of the Ge(Li)-NaI(Tl) coincidence apparatus . . . . . . . . 36 Results of a triple coincidence experiment with the NaI(Tl) annulus and a 7 cm3 Ge(Li) detector . . . . . . . . . . . . . “l Decay schemes of 119Te isomers which was constructed from scintillation and conversion electron studies, compared to those constructed from high resolution gamma ray spectral Studies 0 O I O O I O 0 O O O O O 59 Evolution of the energy level scheme of 1291 as populated by the beta decays of 129m+gTe . 60 Segments of singles spectra of 129m+gTe and 12 ETe, recorded with a 3 cm3 Ge(Li) detector 63 Ge(Li) spectra of l29m+gTe in coincidence with three regions of the spectrum seen by a 7.6 x 7.6 cm NaI(Tl) detector . . . . . . . . 69 A Ge(Li) spectrum of l29m+gTe in coincidence with pulses corresponding to i 150 keV from the NaI(T1) annulus detector . . . . . . 70 A spectrum of 129m+gTe in coincidence with the 28 keV gamma ray . . . . . . . . . 71 Proposed decay schemes of 129mTe and 129%Te . 76 viii Figure 13. l“. 15. 16. 17. 18. 19. 20. 21. 22. 23. 2“. 25. 26. 27. Page 119m Singles spectrum of Te recorded with a 3 cm3 Ge(Li) detector . . . . . . . . 80 119m+g Segments of the Ge(Li) spectrum of Te shown on expanded scales . . . . . . . 81 Singles spectrum of 121Te, recorded with a 3 cm3 Ge(Li) detector after the 119Te had decayed away . . . . . . . . . . . 88 119m Gamma ray Spectra of Te in coincidence with various segments of the 900-l“00 keV region . . . . . . . . . . . . . 91 Gamma ray spectra of ll9mTe in coincidence with the 153 and 270 keV regions . . . . 92 Gamma ray spectra in coincidence with the 6““-700 keV region in 119gTe . . . . . 95 Proposed decay scheme of 1198Te . . . 97 Proposed decay scheme of llnge . . . . 98 Experimental correlation functions for four gamma ray cascades in 119Te . . . . . . 102 Same as Figure 21 for four additional cascades . . . . . . . . . . . . 103 Singles spectrum of 117Te below approximately 1800 keV, recorded with a 3 cm3 Ge(Li) detector . . . . . . . . . . . . 110 High energy portion of a singles spectrum of 17Te, recorded with a 7 cm3 Ge(Li) detector . . . . . . . . . . . . 111 Results of a triple coincidence experiment on ll7Te recorded with a 20.3 cm x 20.3 cm NaI(T1) split annulus and a 7 cm3 Ge(Li) detector . 11“ Coincidence Spectra of 117Te obtained with a 7 cm3 Ge(Li) counter and a 7.6 x 7.6 cm NaI(Tl) crystal . . . . . . . . . . 117 117Te The proposed decay scheme of . . . 119 ix Figure Page 28. Low lying levels in 52TeN isotopes . . . . 123 29. Low lying levels in SleN isotopes as observed in 8-7 decay (9,“5) and (3He,d) and (d,d') experiments (5“-56) . . . . . . 125 30. Comparison of levels in 119Sb populated by beta decay to those observed in (3He,d) reactions (Bu-'56) o c o o c o o e o 132 31. Comparison of 117Sb levels populated by beta decay to those observed in (3He,d) reactions (514-56) 0 o o o o o o c o o o o o 133 32. A comparison of energy levels below 1 MeV in odd mass iodine isotopes . . . . . . . 1“3 33. A comparison of the observed low lying energy levels in the odd mass antimony isotopes . . l“6 3“ A,Typica1 room temperature diode characteris- tics of a Ge(Li) detector §.A schematic illustration of a Ge(Li) drift apparatus . . . . . . . . . . . . 170 35. A schematic flow chart of the MIKIMAUS program 179 LIST OF APPENDICES Appendix Page A. Beta and Gamma Decay Selection Rules . . . 158 B. Manufacture of Ge(Li) Detectors . . . . 167 0. Interpretation of Angular Correlation Data 0 o c o o o o o o o o o o 172 D. Description of the MIKIMAUS Program . . . 176 xi INTRODUCTION In order to test the validity of current nuclear models, it is necessary to obtain a set of eXperimental measurements that is as complete as possible. The models themselves, although usually abounding with empirical parameters, are a measure of our understanding of nuclear structure. Advances in this understanding can be expected to be reflected by improved agreement between experimental results and theoretical calculations. Moreover, while experiment is a necessary test for theory, it can also serve as a motivation for new concepts. The region chosen for this study, Just beyond a major closed Shell at Z = 50, has two main features of potential value. First, because of the existence of a large number of stable tin and tellurium isotopes, many nuclei are readily accessible through proton or neutron bombardments. Hence, one can hope to obtain informatiOn for a large number of similar nuclei. In particular, a comparison can be made of the low-lying energy levels in successive odd-mass isotopes in an effort to obtain information about the effects of the addition of neutron pairs. Second, one of the current nuclear models, the core-coupling model, is best applicable near closed major shells. This model considers a nucleus as composed of an even-even core plus an extra—core nucleon(s) (1-5). The description of properties of even-even nuclei in terms of collective oscillations has been rather successful. Hence, it is of interest to extend this treatment to odd-mass nuclei by coupling the motion of the extra particle to that of the even- even core. This description should be applicable to antimony isotopes (N even, Z = 50 + l) and, to a lesser extent, to the isotopes of iodine (N even, Z = 50 + 3). A second-type of calculation, based on pairing and quadrupole forces, has also been applied with a fair degree of success to this region of the periodic table (1,6). This latter treatment is somewhat more general in that it considers interactions among all particles outside closed shells. This, and the core-coupling model, are similar in that both recognize properties characteristic of collective motions of the whole nucleus, and both attempt to treat nucleons outside of closed shells via "residual interactions." These residual interactions are small compared to the Shell model potential. The primary difference lies in the fact that the pairing plus quadrupole calculation deals with more particles, and hence is more general and can be applied to a larger region of the periodic table, while the core-coupling treatment, at least in its present form, is limited to regions where all but only a few nucleons can be considered to make up a tightly bound core. The experimental methods employed in this study were those of gamma ray spectroscopy. This approach has become significantly more valuable recently as a result of the develOpment of high resolution Ge(Li) detectors. Although all of the decay schemes studied here had been investigated previously with scintillation counters, a wealth of new information wasobtained from experiments utilizing Ge(Li) detectors. In most cases, existing decay schemes had to be modified considerably to accommodate all of the new transitions and to be consistent with high resolution coincidence data. Beta and gamma decay selection rules, which are discussed in Appendix A, limit the number of levels which can be pOpulated in beta and subsequent gamma decay. A further restriction is imposed by the available beta disintegration energy. These dis- advantages are partially circumvented by the existence of nuclear isomerism in the region which was studied. Hence, a much richer decay Spectrum could be obtained, with access to both low and high Spin levels. An additional limitation on the nature of the experiments is imposed by the halflife of the parent. Studies in this investigation were made, with reasonable success, of activities as short as 1 hour. The parent isotopes chosen for this study were 119 129T 117Te, Te, and e. The first two of these decay to the corresponding isotOpes of antimony, while the 129 119 129 I. The Te and Te third populates levels in both have longer lived isomeric states which were shown to decay to sets of states different from those populated by the ground state activity. No isometric state was found in 117Te. The particular choice of'isotopes was made to be compatible with an overall effort in this laboratory to obtain systematic information about the energy level structure for a large number of odd proton-even neutron isotopes in this region of the periodic table. Levels 121 125Sb, 1238b and Sb have recently been investigated 117 in (7-9), making 119Sb and Sb logical choices for continuation of the study. Of those iodine isotopes 127 which are accessible via beta decay, I had also been recently studied (10), while 1311 was investigated concurrently (11) with the 1291 reported here. AS mentioned previously, the information which can be obtained in this type of investigation is limited by beta decay endpoints, by beta and gamma decay selection rules and by limitations on experimental equipment. Hence, to present a fair test to theoretical predictions, these data should be supplemented with results of other types of experiments, such as stripping and pickup reactions and Coulomb excitations. These experiments can be expected to populate some additional states which may be inaccessible to beta decay. Moreover, comparisons of relative population rates in the various types of experiments could conceivably present a key to the particular mechanisms of formation of some excited states. CHAPTER I NUCLEAR MODELS Since one primary objective of this investigation is to compare experimental results with predictions of current nuclear models, brief discussions of these models are presented in the following sections. These are not intended to be exhaustive theoretical treatments, but merely summaries of the main ideas involved, with the hope of putting the subject of nuclear models into proper perspective for comparison with experimental results. 1.1. The Shell Model Among the earliest motivations for a shell model (12) was the occurence of the so-called "magic numbers." Nuclei with either Z or N = 2, 8, 20, 28, 50, 82 or 126 exhibit several characteristic properties. First, there is a greater than normal abundance of stable nuclei of this type. For example, Z = 50 has ten stable isotopes, compared to only two each for Z = “9 and 51, eight each for Z = “8 and 52, and two and one, reSpectively, for Z = “7 and 53. Similar trends can be seen in regions of other magic numbers. The tendency of nuclei which are two nucleons removed from a magic number to be more stable than those with one or three nucleons removed, Should be noted. Second, magic number nuclei are especially tightly bound, deviating significantly in experimental binding energies from values predicted by most semi-empirical mass formulas. Another characteristic, which indicates the reluctance of magic number nuclei to change their configurations is a sharp drop in thermal neutron capture crossections. For nuclei with N = 50, 82 or 126, this crossection is smaller by factors of 10 to 100 than for neighboring nuclei. These properties led Mayer (13) and Haxel, Jensen and Suess (1“) to postulate the existence of a Shell structure analagous to that for atomic electrons. An immediate problem arose from the fact that, while the Coulomb interaction for electrons is well understood and can be treated even for departures from point charges, the nuclear interaction is comparatively only slightly understood. The assumption has been made that each nucleon moves in an average, Spherically symmetric potential V(r) which is due to all of the other nucleons (12). Two restrictions are imposedxon V(r) by the Short range of nuclear forces and by a presumed approximately uniform nucleon distribution throughout the nucleus. The first of these requires that V(r) go to zero rapidly for r > R 0-1“ (R = 1.“Al/3 x 1 cm = nuclear radius), while the second prevents singularities at r = 0. Two common potentials yielding energy level sequences which would result in magic numbers are those of the infinite square well and isotropic harmonic oscillator. However, these potentials, or a more realistic potential obtained from combining the two, give sets of magic numbers which include only 2, 8, and 20, and are each in error for the higher values. A reconciliation can be obtained if an £52 term is added to the potential. Evidence for such a spin- orbit force is suggested by polarized proton beams resulting from scattering by light nuclei. Whereas the energy eigenvalues of the isotropic oscillator are de- generateiflorbital angular momentum, deformation of this potential toward a square well removes this A - degeneracy. Next, the addition of an g-s term to the new, deformed oscillator potential makes the energy also dependent upon the total angular momentum j. Expanding flfi gives: 2 33.8. = 3:1 - 1'1 - i'i which reduces to: z + 1/2 2-1/2 1 for j -(1 + 1) for j II II 2£o§= where A, s, and j are the orbital, Spin, and total angular momenta, respectively. Hence, for a given 2, the j = 2 : 1/2 levels are expected to be Split by an amount proportional to 21 + 1. This now leads to a set of levels which can be made to account for all of the magic numbers. A schematic diagram of this set is Shown in reference 12 and many other texts. If one now begins to fill such a set of states and simultaneously inspects existing data, a number of features become evident: (1, l2). 1. To be consistent with the exclusion principle, filled shells and subshells should have the total angular momentum J = 0. Such is the case experimentally. 2. Empirical evidence suggests a tendency for nucleons in an unfilled sub-Shell to pair off to zero resultant angular momentum, leaving the unpaired particle to determine J of the whole nucleus. 3. Because of a neutron excess for all except the light nuclei, neutrons and protons fill different sub— shells essentially independently. Because of this and number 2 above, all even-even nuclei have ground state J = 0. “. As a consequence of angular momentum coupling rules, an i-Sub shell which is more than half filled can be treated as containing "holes" (equal to the number of missing particles), which behave as particles. 5. In a few cases where two different subshells are close in energy, the pairing tendency favors a pair in the shell with the higher 2 value at the expense of an unpaired particle in the lower Shell. lO 6. In nuclei where both proton and neutron numbers are odd, the odd proton and neutron couple to give the resultant J. The coupling, in general, follows what are often referred to as Nordheim's rules: Let jp,£h,and jp,£h,denote the total and orbital angular momenta of the proton and neutron, respectively. Define Nordheim's number N as: N=(J‘ -2p)+(Jn-£n) then, for a given nucleus, ifN=0 ————>J=|Jp-Jnl and ifN=+ >J=|j -jlor _. {jg-+5]; These are sometimes referred to as the strong rule and the weak rule, respectively. Among the phenomena which can be accounted for, at least qualitatively, by a shell model are nuclear isomerism, beta decay transition rates, and magnetic moments. In some cases, it is possible to have closely lying levels| wherejh%ois the electric (o = E) or magnetic (0 = M) l3 multipole Operator of order L, and J is the spin of the 1 initial state. In regions of deformed nuclei (where both Z and N are far from closed shells), B(E2) values are typically lO-100 times greater than expected from calculations for Single particle transitions. In the spherical region (i.e. near closed Shells) even-even nuclei show (15) an energy level structure similar to that shown in Figure l. The salient features are the spins and ratios of the energies of the excited states. The ground and first excited states have spin parity 0+ and 2+ respectively.. A closely spaced triplet + and “+, though not necessarily in that with J = 0*, 2 order, has sometimes been found to exist at approximately twice the energy of the first excited state. A 3_ level and other negative parity states are often also found near the 0*, 2+, A+ triplet. The low energy level structure in the deformed region (far from closed shells) is also illustrated (15) in Figure l. The energy ratios are typically E“/E2 = 3-3, E6/E2 = 7, and E8/E2 = 12. To explain these features, Bohr and Mottleson (l6, 17) proposed a hydrodynamic model based on the motion of surface shapes of an incompressible fluid. The equation R( 0,4) = RO[1 “a a“ Y: (6.49] 1“ 2* L360 6* 1.155 LF—«LZZB 2* 1.210 (0*) 1.150 (8*) .927 6* ,546 2* .556 4* .266 _2_* .082 0+ 0* 154 114 628 m 48C d ROTATIONAL VIBRATIONAL Ric. 1 Examples of rotational and vibrational enerrv levels which are characteristic oP even-even nuclei in the deformed and the Spherical recions, respectivelv, of the periodic table. 15 locates a point on a surface of general Shape. The time dependence of this point is contained in the coefficients “Au = 01Au (t) RO is a constant, and Y: (8,@ are the spherical harmonies. The Hamiltonian for such a surface can be written as 2 J o 2 H - T + v - l/2AE [BAIa | + Okla Au Aul This is in the form of a harmonic oscillator Hamiltonian with the coefficients BA and CA corresponding to inertial and surface tension parameters, respectively. Terms of order A = 0 are ignored since they correspond to density changes of the nucleus as a whole. This can occur, but only a very high energies. Similarly, A = 1 terms are drOpped since they correspond to the motion of the center of mass. Solution of the oscillator equation gives excitation energies of the nuclear states as § nA‘n wA, where wk = JCZ7BZ— is the frequency of oscillation. Hence the energy of the nucleus can be interpreted as due to “A phonons, each having energy‘UwA. Furthermore, it can be shown that each phonon carries angular momentum with 2 component A and parity (-)A. As A = 0, 1 terms have been ruled out, the lowest phonon states are of quadrupole (A = 2) nature and would 16 be expected to have energy E = fih2 and J" = 2+. The addition of a second A = 2 phonon would give rise to a + state at E = 2 hm and Jr a 0+, 2 , or “+, which is in 2 good agreement with experimental evidence in the Spherical region if one realizes that the degeneracy of the two- phonon states can be removed by secondary interactions which are outside a strict oscillator framework. Moreover, a semi-classical treatment of BA and CA indicates that w3 =2w2 and mu =3w2. This is in agreement with experimental evidence for negative parity states near the two A = 2 phonon triplet. To describe the deformed shapes, one can Specify the orientation of a nucleus by the Euler angles of the principal set of axes of the nucleus with respect to a set of Space-fixed axes. Then other parameters can be introduced to specify the nucleus with respect to its principal axes. The surface equation for quadrupole shapes can be rewritten with respect to the principal axe S as l R = R0 [1 + a a2“ Y; (e , ¢ )1 where the a are related to the a through the angular 2n 2n momentum D—matrices. Because principal axes are used, only the a2O and a22 = a2_2 coefficients are non—zero. New parameters, 8 and y, can be defined as a20 = 8 cos y and a22 = 1/2 8 sin y. 17 Interpretations of B.and y as parameters for the total deformation and for.the shape, respectively, is illustrated if one writes increments of length of the principal axes, GRk = HTT' R0 8 cos( y- k g" ) The terms of the Hamiltonian for the system become, after transformation of coordinates, 3 .2 = 2 ° 2 2 T 1/2 B (B + B Y ) + l/2rz=l $18k wk and v = 1/2 c 32! where in the rotational type term, 3k are effective moments of inertia and the 3 is the angular velocity of the Space fixed axes with respect to the body fixed axes. If an axis of symmetry exists, then 93 = 0 and 31 = .92 = S = 38B2. Thus, the'Hamiltonian can finally be written as The first and second terms of the Hamiltonian to B and y vibrations, respectivgly. The third term can be 3 kél "ng angular momentum components with respect to the moving rewritten as Hrot = where the Lk are axes. If the 3-axis is a symmetry axis, then L3 = K is a constant of motion along with the total rotational angular momentum L2 = J(J+l) and its projection on the 18 z axis, LZ = M. The energy eigenvalues for this term are rot == Egg JKJ'+ 1). It can be shown that if K = 0 the wave functions vanish for odd values of J. Hence, nuclei with an axis of symmetry are expected to exhibit the 2+, “+, 6+, 8+ structure shown in Figure 1. This structure is best observed in highly deformed even-even nuclei. The high deformation, 8, is necessary to make E = 38B large, making EJ in turn small compared to other types of excitations, while the even—even condition insures that Jintrinsic = 0. Furthermore, the energy ratios of the rotational levels are seen from the expression for Er to ot be E“/E2 = 3.33 E6/E2 = 7, E8/E2 = 12, etc., in good agreement with observed values. 1.3. Particle-Core Coupling Model Since the collective model works so well for even-even nuclei in many regions of the periodic table, it is natural to attempt to extend it to odd-mass nuclei in these sameregions. If the properties of the even- mass isotopes are well explained by collective motions of all the particles, one would expect that the addition of an extra particle Should lead to a behavior resembling that of the even—mass core but modified by the presense of the extra particle. For the most part, the summary of the core-particle coupling treatment follows the more detailed presentation of Preston (1). 19 The Hamiltonian for such a system should then be expressed as where the subscripts c and p refer to core and particle, respectively. Questions which arise are concerned with how one describes the core-particle interactions, and, for cases where several particles are outside closed shells, what constitutes a core. In the Simplest approximation, the second of these questions can be disposed of by assuming the core to be made up of all paired particles. More ambitious schemes would consider the core to be made up of closed major shells and subshells only, necessitating treatments of one or more extra-core particles (or holes). The introduction of small residual interactions among particles outside closed shells is sometimes referred to as the "intermediate coupling" scheme. The particle states obtained in this manner are then used as the particle states in particle-core coupling calculations. The other question, that of the particle—core interaction, can be discussed in two extremes, the "strong" and "weak" couplings, with a poorly defined boundary or overlap between the two. A coupling is considered "strong" if a permanent deformation exists, significantly changing the "average shell model potential" experienced by the particles. In the other extreme, near closed shells, the coupling generally leads to only very small deformations 20 from sphericity. Hence, in the spherical regions, perturbation methods should be applicable. 1.3.1. Weak Coupling In the weak coupling approximation the interaction is added as a perturbing term _ o H - HC + Hp + Hint The term H; is taken to be the spherical single particle Hamiltonian and H is expressed in terms of the int deformation parameters ”Au and the Spherical harmonies as n ' u for "n" particles outside the core. In most calculations, the coupling parameter k(ri) is treated as a constant for a given nucleus, with allowances for variations with mass number. The states of such a system with angular momentum J are formed by vector addition of the single particle state Ijm>, with angular momentum j, and the collective state INR>, with N phonons and angular momentum R. Diagonalization of H then yields the new set of states with the new set of energy levels. Several semi- quantitative generalizations can be made from the application of perturbation methods in the quadrupole approximation: 21 1. For perturbation techniques to be applicable, it is necessary that (ESL-671‘) 1/2 5%1/2 <<1 where‘hw is the phonon energy and C is the oscillator potential constant. This, as has been mentioned previously, can be expected to hold in the spherical regions. 2. Because of the second order Spherical harmonic Y: , only those single particle states which have the same parity and a Spin difference :_2 will mix. 3. For appreciable mixing to take place, the states must be close in energy. “. Vibrational levels may be built upon the ground state or upon single particle excitations. Thus, each phonon - particle coupling will yield a set of the smaller of (2j + l) or (2R + 1) states. The degeneracy of these is removed by the admixture of other particle or phonon states. 5. The center of gravity of a multiplet of core— particle states in an odd-mass nucleus should occur at the same energy as the corresponding collective state in the neighboring even-even nucleus. A general form of this center-of-gravity theorem was first presented by Lawson and Uretsky (l8). 6. Since a has been shown to have non-zero 2n matrix elements only between states which differ by 22 exactly one phonon, deexcitations of two-phonon coupled states should occur via cascades involving at least two transitions. One of the first calculations of the core-coupling type was performed by deShalit (2), in which he considered the coupling of j = 1/2 particle states to 2+ and 0+ phonon levels for a number of isotopes in various regions of the periodic table. In the same paper deShalit derived general expressions for first order Shifts of the coupling multiplets and expressions for transition probabilities. More recently calculations have been performed on several odd-mass iodine isotopes by Banerjee and Gupta (3),by O'Dwyer and Choudhury (“), and by Silverberg (19). 129 Those dealing with I will be discussed in more detail in Chapter IV. 1.3.2. Strong Coupling When large permanent deformations are present, the interaction term can no longer be obtained from a first order expansion of the potential about its equilibrium value in terms of the deformation parameters, as was possible for weak coupling. In this case the deformation parameters are embedded in the expression for the potential well, yielding a set of generalized shell model single particle states. Values for the parameters 23 B and a are obtained by minimizing the total particle energy, giving rise to a self-consistency problem for the potential. If one assumes that the nuclear orientation changes much more rapidly than does the shape, then 8 and.v can be treated as approximately constant in the particle potential, and a rotational term can be separated from the particle Hamiltonian H = T + 2 H rot p p 3 _ -2 Trot i=1 Bk 2 3k The angular momenta to be considered are J, R, and j for the whole nucleus, the core, and the extra-core particle(s), respectively, and are related through J ”.5 +‘j. In general, the treatment for the strong coupling case becomes considerably more complicated than for weak coupling. One simplification is obtained for the case of axial symmetry. The energy levels of the axially symmetric system are characterized by a Single particle energy and a set of rotational levels built upon the single particle state. The expression has been shown to be 2 J+1/2 EJK = eK + (§%)2 [J(J+1) - 2K +5K,1/2 a (—) (J+1/2)] 2“ The quantum numbers J and1< represent the total angular momentum and its projection on the symmetry axis. The parameter "a" is called the decoupling parameter and consists of a combination of admixture coefficients from the wave function.’ The KrOnecker delta arises from expansion of R: = (J - j) ' (i,‘ j) and corresponds to terms which include raising and lowering operators J: j+. The properly symmetrized wave functions include both :K components, hence only K = 1/2 states will yield non-zero expectation values for operators involving J: j;. Physically, this term corresponds to a Coriolis type interaction. Single particle states in distorted nuclei were first studied by Nilsson (20). for the axially symmetric nuclei and later by Newton (21) for the general case. Nilsson's treatment consists of a number of approximations and transformations, leading eventually to a wave equation for an anisotropic oscillator plus correction terms. The oscillator solutions can be obtained in either Cartesian or pseudospherical coordinates. The states are characterized by quantum numbers Inl n2 n > and IN,2,A,£> 3 for theCartesian and pseudospherical case, respectively. The numbers n1, n n correspond to the numbers of 2’ 3 excitations along the three axes, while N = nl + n2 + n3. The number 2 is the eigenvalue of a pseudo angular momentum operator A, defined in terms of the transformed 25 position and gradient operators. The eigenvalue of A3 is A, and Z = : 1/2 is the value of the spin component S 3. The correction terms in the Nilsson Hamiltonian are CA ' g and DA2. The first of these corresponds to the Spin-orbit term of the spherical Shell model potential. The second term was found necessary to lower the energies of oscillator states of high angular momentum. Numerical solutions for this system have been published by Mottelson and Nilsson (20). The parameters C and D were chosen so as to give the shell model results for Spherical nuclei. Then the splitting of the various shell model levels was plotted as a function of the nuclear deformation. A number of calculations have been performed for deformed nuclei and the strong coupling. Among the best known of the more general treatments probably are those of Davydov (22). Pashkevich and Sardaryan (23) have 1198b 3 applied the treatment for non-axial nuclei to among others, which is one of the nuclei studied in this thesis. 1.“. Nucleon Correlations While the Simple shell model provides good qualitative explanations of many pheneomena, quantitative discrepancies generally exist when one considers excited state energies, transition probabilities, moments, etc. 26 This should not be surprising, Since only particles in average potential wells have been considered, with no provision for interactions among particles in unfilled shells. What is, in fact, surprising, is that in spite of a known very strong nucleon—nucleon force, the interaction between these nucleons is no larger than it is. Hence, it is possible to write the Hamiltonian as the sum of two parts--a part containing all of the ingredients contributing to the average (shell model) potential well and a "residual interaction" term. One fairly successful treatment considers the residual interaction as made up of a Short range pairing force and a long range quadrupole interaction (1). That a pairing force of some kind exists is suggested by empirical evidence. The pair is assumed to have identical quantum numbers except for opposite spin projections. Then the pair is assumed to move in a correlated manner, along with other pairs, over several available single particle levels. Hence, the wave function of the pair may contain admixtures of many Single particle states. The excitation of a pair will result in a different admixture of states in the wave function of the pair, and, because of the exclusion principle, will also cause a change in the wave—functions of other pairs. The long range part Of the residual interaction is taken to be dependent upon the quadrupole operator r2 YB. 27 This "quadrupole interaction" is largely reSponSible for collective motions of the whole nucleus. The solution to the system is obtained by first solving for the pairing force and then treating the quadrupole interaction by perturbation methods. The wave function is written as a combination of single particle states ljm>, weighted by the probability amplitudes UJ (VJ) that the state is unoccupied (occupied). One condition on UJ and V3 is that U? + V? - l. The quantities UJ and VJ are also defined in terms of other parameters as e - A U2 = J 1/2 [1 +q7;3 _ 1)2 + A2] 92-). _i==e— 3 1/2 [1 ’JFeJ - A)2 + 22] <1 II where 23 is the single particle energy arising from the shell model well. The other parameters, A and A, can be interpreted as an average Fermi energy and a measure of the thickness of the Fermi energy surface,respectively. These can be obtained from N, the number of particles outside the closed shell, and G, the coupling parameters of the pairing interaction, where 2 J 2 ll 2 (2i + 1) V J and l> ll G3 and a hole in Ij, — m >, with in the wave function. This appropriate weights U and V J J transformation results in a set of quasi—particle wave functions in which the Shell model plus pairing Hamiltonian is diagonal. Then, with this set as a basis, the quadrupole interaction can be treated by perturbation methods. The quasi-particle energy in a state j (neglecting the quadrupole interaction) is given by _ _ 2 1/2 EJ - [(eJ A) + A ] Since the quasi-particles are non-interacting, the energy spectrum of the system is obtained from the sum of the individual quasi-particle energies EJ , EJ + EJ , EJ + l 1 2 l E + E , etc. J J 2 A ialculation based on pairing and quadrupole forces has been performed by Kisslinger and Sorensen (6) for nuclei from nickel to lead. In this work the single particle energies were chosen once for all nuclei in a large region of the isotope table. But allowance had to be made for smooth variations in these levels with A in order to obtain reasonable agreement with experiment. Furthermore, different level spacings had to be used for neutrons and for protons. Since neutrons and protons fill 29 separate shell model levels, only pairing between protons and neutrons separately was considered. However, neutron- proton quadrupole interactions could not be excluded. The coupling parameters G were taken to be equal for protons and for neutrons, i.e. Gp = Gn = G, as were the quadrupole force strength constants X, i.e. Xp = Xn = an = X. Allowances for a mass dependence in both G and X were made. CHAPTER II EXPERIMENTAL APPARATUS AND METHODS AND SOURCE PREPARATION While many standard eXperimental techniques were employed in this investigation, several new methods were developed. The first few of the following sections give brief descriptions of the experimental apparatus. The rth sectionssummarize the data handling techniques which were employed to facilitate a more rapid and accurate analysis than was possible previously without computers and without the high resolution data recording apparatus. Finally, the last section of this chapter deals with the production and chemical separation of the various tellurium isotopes whose decay schemes were studied. 2.1. Ge(Li) Singles Spectrometers The development of lithium drifted germanium, Ge(Li), detectors in the last two to three years has made possible the observation of many new gamma rays in complex spectra. An improvement of a factor of about 10 in the resolution of the Ge(Li) detectors over that of NaI(T1) scintillation counters has resulted in the identification of many low intensity gamma rays which are buried by strong neighboring transitions in 30 31 Spectra recorded with the NaI(Tl) detectors. However, major drawbacks in the Ge(Li) detector are a very low photOpeak efficiency, and a very high ratio of Compton to photo electric events. The latter of these is especially bothersome in spectra containing intense high energy gamma rays whose Compton distributions can easily obscure less intense lower energy transitions. Both of these disadvantages are presently being reduced by large 3 volume detectors (~10 - 30 cm as compared to =lcm3 for the original counters). The larger volumes increases not only the probability of a photoelectric interaction in the detector, but also the probability of secondary events, i.e. interaction of Compton scattered photons before they escape from the crystal, as well. The effect of larger volume on the full energy peak can be seen in Figure 2, which Shows relative efficiency curves obtained for three detectors of different volumes. The manufacture and principles of Operation of Ge(Li) counters have been extensively discussed in the literature, which includes at least two detailed reports (2“, 25). A brief summary of the methods employed in this laboratory is given in Appendix B. In order to derive the maximum benefit from solid state counters, it is necessary for the associated electronics to have very low noise characteristics and high stability. The best resolution obtained so far in RELATIVE EFFICIENCY ICLO 'o (ARBITRARY UNITS) .0 (LOI 32 FULL ENERGY PEAK EFFICIENCY OF GEILI) DETECTORS Active Volumes 8 . 3 A: e: 30 cm 8= 2 7 cm3 3 C 0 2 3 cm Source at z 9 cm 1 1 IO IOO IOOO IOOOO ENERGY (KEV) Fig. 2 Relative photopeak efficiency curves for three Ge(Li) detectors. Data for curves A and B were recorded with sources approximately 9 cm from the nearest face of the detector. Data for curve C were re- corded at a different time, and the reference point for this curve has been adjusted so that the results approximately correspond to the counting conditions for curves A and B. 33 3 detector of this laboratory has been with a 0.8 cm approximately 10 pf capacitance, used with an ORTEC 118 room temperature FET preamplifier, a Tennelec TC—200 amplifier, and a Nuclear Data 102“ channel analyser. The full width at half maximum (FWHM) for the 662 keV line emitted by 137Cs, was approximately 2.8 keV. Typically, resolutions have been approximately “-5 keV FWHM for 13705. Various mounting systems have been employed in the laboratory, the most popular being a "dip-stick" arrange- ment. It can be seen as part of the multiple coincidence spectrometer in Figure 3. 2.2. Ge(Li)--NaI(Tl).Coincidence Spectrometers Lifetimes of nuclear states deexcited by gamma decay are short, typically within a few orders of magnitude of a nano-second. Thus, gamma rays emitted in the deexcitations of successive levels can be effectively considered to be emitted simultaneously. It is therefore possible to use two detectors to record coincident gamma rays, suggesting gamma ray cascades. By considering energy sums, relative intensities, and coincidence relationships among the various gamma rays present in the beta decay of an isotope, it is usually possible to construct a unique scheme of the energy levels populated in that decay. 3“ mil—11m JIIIIIIIIIIIIII xr~6—RCA 8053 PHOTOMULTIPLIERS / /“‘“— ,/ //// A 11 /'/,’ I. //—TEFLON / I " V‘ 1/’ VI A r Mp" ‘- - 8 66m ”4-17 / V 2 AL 20.3 cm 0.0. X A I ' ” 9.2 cm 1.0. x f . 20.3 cm LC. 7" u r_JG€(LI) rfl/ “,4 J / 1 , X . NoIITI) 9/. I L31 J L A V V d r w I” \ \ 1%, f r \ ‘~ A N * 1 / F \HN H MD I. 1 I. /1 [1//’1 \‘\ 'O‘A'AHJA’ \Q‘ $5, TO PREAMP , K \‘ STAINLESS K, .\ /—Cu 6‘ \‘x\ , \. MOLECULAR suave A 1i31\\ . Fig. 3 Cutaway view of the Ge(Li) - NaI(Tl) annulus coinci- dence spectrometer (from ref. 26). Only two of the six photomultiplier tubes are represented. The lead collimator is used primarily in recording anti- compton and double-escape spectra. 35 The advantage of excellent resolution in Ge(Li) counters can be carried over to coincidence experiments, but only at a considerable sacrifice in counting efficiency. However, as is evidenced by some of the complex Spectra discussed in section 3.2, the Ge(Li)-- NaI(Tl) coincidence combination is essential if most of the ambiguities of the proper relationship of the gamma rays in the decay of a nucleus are to be resolved. 2.2.1. Conventional Coincidence Experiments The experimental coincidence counting arrangement is schematically illustrated in Figure “. In general, only a narrow segment of the Spectrum seen by the NaI(Tl) detector was selected by the single channel analyser. Then those events in the Ge(Li) detector, which were in coincidence with this region of the NaI(Tl) spectrum, were recorded in the analyser. To avoid gain drifts during the long counting times involved, it was often found desirable to enclose a large share of the apparatus in a styrofoam box, in which the temperature was controlled to within :0.5 0°. Because of the large amount of Compton scattering out of the Ge(Li) crystal, either shielding and/or careful geometric orientation of the crystals was necessary. 36 Cathode Follower ._.___T__.._J I 1 I l.__ NaI(T1) P m V/ a tea p ’/ Source Linear Amplifier Cosmic 901 _1___, 7% L 1 I Single ’ Analyser Ge(Li) 4§;¢/ Preamp Tennelec 130(FET) - Ortec 118 (PET) or Tennelec 100 C Pulse Shaper Linear Linear Amplifier Amplifier Cosmic 901 TC 200 Single Channel Analyser Channel ‘ COSMIC 801 I Fast — — —> To analyser (display) for setting gates To Analyser (display) ’47 To Analyser (gate) .Fig. “. A schematic illustration of the Ge(Li)—NaI(Tl) coincidence apparatus. 37 2.2.2. Experiments Utilizing a Split-ring NaIITl) Annulus A Ge(Li)--NaI(Tl) coincidence system employing a 20.3 cm x 20.3 cm Split ring NaI(Tl) annulus was used for some experiments. Since this system is discussed in some detail elsewhere (26), only a brief description will be presented here. The detector arrangement is illustrated in Figure 3. If the gamma rays are collimated into the Ge(Li) counter as Shown, the system can be used either as an anti-Compton or as a double escape Spectrometer. In the former case, because of the Shielding from the collimator, the majority of the pulses which arise from the NaI(Tl) crystal are those due to Compton scattering from the Ge(Li) crystal (and its mount) into the NaI(T1). Hence, by closing the analyser gate whenever simultaneous pulses are detected in the solid state counter and in the annulus, most of the Compton events occuring in the Ge(Li) counter are rejected from the Spectrum. One serious drawback to the arrangement, as Shown, is that the Compton crossection favors scattering back toward the source. Hence pulses corresponding to Compton knees are less likely to be rejected. In fact, if the Ge(Li) counter is lowered further, decreasing the solid angle through which scattered photons may escape from the annulus, the Compton knee takes on a peak-like appearance, and can cause some confusion in complex spectra. So far, attempts 38 to insert low Z material above the Ge(Li) counter for the purpose of directing some of the backscattered photons to the annulus through secondary scattering, have not yielded significantly improved.results. ‘An improvement can be obtained if a 7.6 cm x 7.6 cm NaI(Tl) crystal is inserted in the top portion of the hole and is used together with the annulus. However, in this case the source must be placed inside the annulus and a loss of counts due to coincident gamma rays will result. The application of this system as a double escape spectrometer is probably the most impressive. Because of the split crystal, it is possible to require Simultaneous Signals from both halves of the annulus and from the Ge(Li) counter (i.e. triple coincidence experiments). If the window for each half is set to include only signals corresponding to 511 keV, then the only events, in principle, which are counted by the Spectrometer are those in which a gamma ray interacts with the Ge(Li) counter by pair production, with one of the subsequent annihilation quanta being detected by each half of the annulus. If an uncollimated positron emitting source is placed inside the annulus, gamma rays which are in coincidence with annihilation radiation following 8+ decay are also recorded in the Ge(Li) spectrum. That events due to multiple scattering and to chance coincidences are [A practically eliminated can be seen in some of the figures E presented in the next chapters. 39 Other useful applications include triple coincidence, any-coincidence, and anti—coincidence experiments. For all of these, the collimator is removed and the source placed close to the Ge(Li) counter. The usefulness of triple coincidence experiments for identification of cascades should be obvious. The any-coincidence and anti-coincidence are, in a sense, complementary experiments, but represent a tool with a subtle power which is not fully appreciated in general. Since integral gates with low discriminator settings are generally used, the Compton as well as photo events in the gating NaI(Tl) annulus detector can trigger a coincidence signal, increasing the overall coincidence efficiency. Thus, a comparison of relative intensities in these spectra to relative intensities in singles serves to immediately establish any levels which are populated by beta decay only and de-excite directly to ground. In addition, these relative intensity measurements can suggest cascades and can indicate which transitions originate from heavily gamma fed levels. Extra caution must sometimes be exercized when interpreting coincidence spectra recorded with very large detectors such as the annulus. Because of the large solid angle subtended by the NaI(Tl) detector, more than one gamma ray of a given cascade may be detected by this crystal, giving rise to a pulse corresponding to the sum of the energy of the two gamma rays. Because of this “O summing, coincidence events may be lost from the Ge(Li) spectrum Since the NaI(Tl) pulse will no longer fall inside the gate region selected by the coincidence circuitry. A major advantage of this summing is a "clean up" effect on Compton backgrounds. The.Compton scattered gamma ray from the Ge(Li) counter may also be picked up by the annulus detector. Since the resulting pulse from the annulus will no longer satisfy the gate requirements, that Compton event will not be recorded in the Ge(Li) Spectrum. A striking example of this effect can be seen in Figure 5, which shows triple coincidence spectra from the decay of llnge (This activity is discussed in considerable detail in Chapter 3). Because of summing in the gate the Compton distribution of the 912 keV gamma ray in spectrum B of Figure 5 is essentially absent. 2.2.3. Angular Correlation Experiments One can obtain information about energy level spins and transition multipolarities by measuring the relative angular distribution of gamma rays emitted in cascade. The direction of one gamma ray is chosen as the z—axis, and the coincidence counting rate is recorded at various angles with respect to that axis. A more detailed description of angular correlation experiments and their interpretations is given in Appendix C. 10° 107 5 a 5 o COUNTS (ARBITRARY WITS ) o“ 10' .EL “1 NaI(Tl) annulus and a 7 cm3 Ge(Li) detector. The I I I m I- 3' ~ -fl A. SINGLES 119m T, 3 1 It: _ I 5:2 '3: "" ,. S! N a; 0000 . V l- 1- waJ g n ‘3 . A .. E _ ‘*’~.« I I .i , ‘W. . . N N E r “sud-5.4.” [\ I. g 3 3 JV - ' I" » \\,."_~- 3‘1""! t,3:...-,m,-'.-.:q.‘.,-\-,,‘m.¥“,vf¢'”vali‘eh‘rn.‘ g” g P ‘1 FEN‘F’ "'3. t 3' a. come WITH |53-|64 g ’ i 1| g 1 ”A and 1213 Kcv 9 ~‘., ‘ .0 I ‘Zfl; <3 I 23}. uk. 5 1; - . ' r .,n LA.I I ;.hn. _ tn: ‘2... ' N n . . . .. . _‘ . fkR ._ Ala; § 1 I; s u ~.. .1. ’ ', v3.2 A “-3.1": .,-' J Li“... fl ‘ r- a p lf\. -. r ,I m. 3' i I SII ‘ j " I MI c. com mm 270 2 l I .11 o and 950 -1150 Kev , '7' -. ' h . _ . I N g A .4 . . A K . . - . N * wI _ 831- . . 3...... . r, .1 31.1.1121 . .\:o v.0"~“~ 2%“ . ' [_ 553% ‘ " .39 ' . _ :1;I I A , ':‘§i r A: q 1 I l 100 200 7300 400 CHANNEL NUMBER Fig. 5 Results of a triple coincidence experiment with the pertinent part of the decay scheme being investigated is shown in the upper right-hand corner of the figure. ,A singles spectrum is shown for easier identification of coincident phOtopeaks. Note the absence of the Compton distribution of the 912 keV gamma ray in spectrum 8. H2 The angular correlation apparatus can also be schematically illustrated as in Figure u. In this case the NaI(Tl) detector was mounted on a movable arm which enabled the detector to be rotated from 90° to 270° with respect to a line defined by the center of the fixed Ge(Li) crystal and the source. 'The NaI(Tl) crystals employed were of two sizes-—7.6 cm x 7.6 cm and 5.08 x 5.08 cm. During the course of the experiments, two different Ge(Li) detectors were used. Both of these were of the 5 sided wrap-around type and had active volumes of approximately 20 cm3 and 30 cm3. The best resolution obtained for these detectors was 2 4.5 keV FWHM for the 662 keV line in 1370s. However, since a different preamplifier was used for the correlation experiments and pulse shaping requirements for the coincidence circuitry had to be met, typical resolutions were 2 8 to 9 keV FWHM. The larger of these counters was mounted with the p-type core in a vertical position, while the core of the smaller crystal was in a horizontal position with the open face farthest from the source. Both detectors were mounted in elbow-type cryostats with a liquid air reservoir placed above the coldfinger. To minimize gain drifts in the electronics, the temperature surrounding most the apparatus was kept con- stant to within 1 0.5 C°. In order to compensate for any small drifts which might occur, spectra were recorded at “3 each angle for short periods (typically 40 minutes) only. The final spectra for each.angle were summations over a number of such individual spectra, and included spectra recorded at 360° minus that angle. In this manner first order corrections were also made for small misalignments in the source position and for source decay. A multiple coincidence unit with a variable resolving time was employed, and spectra were simultaneously recorded in the two halves of a 102“ channel analyser. Typical resolving times were g 80 nanosec. Source strengths were of the order of a few microcuries. Typically 103 pulses/sec from the NaI(Tl) detector satisfied the gate requirements. Approximately 0.5% of these were in coincidence with pulses from the Ge(Li) detector. 2.3. x—ray Intensities A 2.5 cm x 3.8 cm NaI(Tl) crystal with a 0.013 cm thick Be window was used for x-ray measurements. The relative efficiency of the detector was checked with 137Cs and 113Sn sources, both of which have x-rays of well-known intensity relative to a gamma ray (15). The energies of these x-rays fell on both sides of the region of interest. No significant absorption by the Be window was observed for x-rays in the 25-30 keV range. The intensity of the x-ray in the "unknown" spectrum was AA then determined relative to that of a prominent gamma ray or group of gamma rays. 2.“. Positron Endpoints Positron endpoints of 117Te were measured with a 0.64 cm thick plastic scintillator mounted on a phototube. Aluminized mylar of 0.0013 cm thickness was used as the window. Energy calibrations were made from conversion lines of 113Sn and 207Bi. The centroids and weighted energies of the composite K and L lines were used. The spectra were recorded with a source distance of several millimeters. After a carbon absorber was inserted between the source and the detector, counts were subtracted from the spectrum in the analyser to correct for Compton events of gamma rays. Positron Spectra were recorded in coincidence with annihilation radiation and in coincidence with the strongest gamma rays de-exciting suspected positron fed levels. Because of source thickness, attenuation in the window and in air, and poor resolution of the plastic, no conclusive evidence in regard to spectral shapes could be obtained. 2.5. Data Analysis In order to take full advantage of the high resolution and accuracy afforded by the Ge(Li) spectrometers, and to facilitate handling large amounts of data rapidly, much 45 of the analysis were carried out.on the MSU CDC-3600 and the MSU Cyclotron Labratory's SDS SIGMA-7 computers. Most of the data were plotted with the CDC-3600 system using modifications of the GRAPH program originally written by T. Rice (27). Energy and relative intensity determinations are discussed in more detail below. 2.5.1. Energy Measurements The energies of the prominent lines in "unknown" spectra were determined by counting the unknown source simultaneously with several standard sources which emit gamma rays of well-known energy. To correct for non- linearities in the system, both first and second order least squares calibration equations were constructed. The peak positions were taken to be the centroids, which were determined after an appropriate subtraction of the background under the peaks. All of these computations were performed by the MIKIMAUS program, which is described in more detail in Appendix D. The errors quoted on the gamma ray energies are based on deviations from mean values obtained from several measurements. The individual runs were weighted by the reproducibility of the standard energies from the calibration curves. A set of typical calibration data with both linear and quadratic fits, is shown in Table l . The non-linearity of the system is readily apparent. It can .mm mocmpmmmm Soup msam> mmpmco mooom e0 zmomo ecu CH pummonmo .mm monopomom Scam 03Hm> zmhmco mmo mo mmomo one CH pcommhm U6 wma n .ma mocmpmmom 80pm 05Hm> mwhocm MHHMH mo mmomo on» CH pcomopmm :mo.o1 s:m.mmma wwm.o mmm.amma :m.mnm omw:.NMHH ooa.o oma.mwaa mmm.o1 mwm.mnafi wm.wms ommm.mmaa mmo.o1 :mo.fimm mmo.a1 mam.mm© mm.qu nmmm.fiom mHo.o :m:.:mm asa.o wam.:©m mo.:mm anmz.:om HHo.o mmm.:wm omm.o wmm.mwm mm.oma wwom.:wm one peg soapMH>oQ oHpmpomsa coaumfi>oa smocfiq Hoccmgo mwsocm NAHmCCMQOV x mm 0000.0 + Aaoccmnov x om:.H + :o:.za u zwposm ”cofipmnofiamo ofiumhomsa “Hoccmnov x :Hm.H + mmm.m u zwpmcm ”coapmpofiawo pmmcfiq mama monumeneflmo Hmefiases1.a magma 117' also be seen that the standards typically reproduced to within : 0.1 keV from the accepted value. Errors quoted on standard energies (such as 1173.226 i 0.0A0 and 1332. A83 : 0.0u6 keV' (25) for the gamma rays in 60 Co) were usually ignored since they are approximately only 10% of the other errors. Once the prominent lines were accurately measured (usually to less than i 0.5 keV), they were used.as internal calibration points for measuring the weaker lines in subsequent spectra. In these cases the uncertainties of the calibration points were taken into account when assigning errors to the weaker lines. It should be pointed out that the accuracy in the energy measurements can be significantly increased if one uses larger analysers such as A096 channel system. The uncertainty in the energy of a peak is dependent upon the error in the position of the centroid of the peak. Hence spreading out the same spectrum over four times as many channels reduces this contribution to the energy error by a factor of four. Namely, an uncertainty of 0.1 channels in the position of the centroid corresponds to 0.2 keV if an analyser calibration of 2.0 keV/channel is used as opposed to only 0.05 keV if the calibration can be increased to 0.5 keV/channel. A further advantage of a larger system arises from the fact that at a lower keV/ channel calibration, the peak will be composed of more points, which will result in a better approximation of a A8 smooth curve. It has been pointed out by Heath et al. in a comprehensive study of energy measurement accuracy (28) that a minimum of 5 channels per peak is necessary to make contributions to the error from finite channel widths negligible. With some of the present detectors (FWHM 3.0 keV) and a 102“ channel system this requirement is satisfied only for energies up to approximately 1 MeV. As counting systems with better resolution become available, a larger analyser will become even more necessary in order to obtain a high degree of accuracy without a sacrifice in resolution. 2.5.2. Relative Intensity Measurements Relative photopeak efficiency curves were obtained in two ways. First, a set of standard gamma ray sources whose absolute intensities were measured with NaI(Tl) detectors were used. However, because of uncertainties in geometry and in NaI(Tl) efficiency tables (29), errors of :10% were assigned to the individual intensities. Second, a set of points was obtained from sources emitting several gamma rays whose relative intensities were obtained from existing decay schemes. An example of an especially good source for this is the decay of 5.6 day l2OSb into 120Sn. All of the beta feeding is to an excited state in 120 Sn which de—excites only by a four step cascade, with no crossovers (30). Hence, all of the transitions at 89, 196, 1022, and 1171 keV are of 49 equal intensity. From the known-mu1tipolarities, only the 89 keV transition has a significant correction for internal conversion. In general, efficiency curves.obtained for a detector by each of the above methods were in very good agreement. Relative intensities of at least the prominent lines in "unknown" spectra were determined with calibrated detectors and in geometry closely matching that used in the calibration. These strong lines then served as internal detector efficiency calibration points in later spectra, making relative intensity determinations of other gamma rays in the spectra approximately absorption and geometry independent. 2.5.3. Angular Correlation Measurements A more detailed discussion of the interpretation of angular correlation measurements is given in Appendix C and in section 2.2.D of Chapter III. This section is primarily concerned with difficulties encountered in measuring the angular correlation coefficients accurately. The correlation coefficients obtained were approximately corrected for the diminutive effects of the finite solid angles subtended by the detectors. The correction for the NaI(Tl) detector was obtained from calculated tables (31). Because of the irregular geometry, calculations become 50 very difficult for Ge(Li) detectors. .It was assumed that an approximate correction could be made from tables for NaI(Tl) detectors of comparable size. That this assumption was not grossly in error was demonstrated by performing the angular correlation measurements on well known cascades (15) present in the decays of 60Co and 152 Eu. Results of experiments on the well known correlations in these two isotopes suggest that the finite siZe detector correction is approximately 5% for gamma ray energies in the 1 MeV region, and increases to possibly 10% near 100 keV. All measurements were performed with the same source to detector distance, 5.2 cm. Peak areas were generally determined as discussed in section 2.5.2. First order corrections for coincidences with Compton events in the gate were made from spectra recorded in coincidence with regions adjacent to the peak. Wherever possible, gates were simultaneously set on the photo-peak and on regions on both sides of the peak. The two Compton gates were of approximately equal width, which, in turn, was approximately one-half the width of the photopeak gate. The outputs of the two Compton coincidence circuits were combined and the resulting Compton coincident spectrum was recorded in that half of the analyser memory which was not used to store counts in coincidence with the photopeak region. 51 Corrections for random coincidence events were made in one of two ways. First, a chance coincidence Spectrum was recorded by delaying the signal from either detector by a time greater than twice the resolving time of the coincidence unit. After any counting time and/or decay corrections, the appropriate number of counts could be subtracted from the true plus random coincidence spectra. ‘A second method was sometimes used if a given line in the spectrum was known definitely to be not in true coincidence with any events of any type in the gate. ”Normalization of a singles spectrum to this line then yielded an appr0priate correction. In general, the gate was set on the higher energy member of a given cascace. The advantages in this case are threefold. First, the greater efficiency of NaI(Tl) relative to Ge(Li) for high energy gamma rays increases the coincidence count rate. Second, in the higher energy regions of the spectrum there are fewer gamma rays whose Compton distributions will fall in the gate. Hence Compton corrections will usually be smaller, and in some cases can be eliminated. Third, because of a decrease in the total number of counts (photo plus underlying Compton) in the gate, the chance rate due to the unwanted gating counts will also be reduced. 52 The errors assigned in the correlation measurements are based primarily on the reproducibility of the correlation function over several measurements, and on the uncertainty in the solid angle corrections. It was found that typically the values reproduced to an average value 1 approximately 10 to 20%. The primary difficulty was suggested to be due to poor statistics resulting from the very low count rates. This, combined with an estimated 5 to 10% uncertainity in solid angle corrections, implies the results to be good to approximately 1 20%. 2.6. Source Preparation The 129Te parent was produced by neutron bombardments of tellurium metal, enriched to 99 per cent in 12are. The l29m+gTe activity was obtained by ‘irradiating 20 mg samples in a thermal neutron flux of = 2 x lOlL‘ncm-2sec"1 for periods of seven days in the ORR reactor at the Oak Ridge National Laboratory. 131 Besides l3lTe and its daughter I, other activities were made in minor quantities. The most significant difficulty was caused by 110 Ag which was present in some aged sources. The 70 minute l29gTe activity was produced by repeated short (7 to 60 min) irradiations of 128Te in a flux of A x 1012 10 mg samples of enriched n ' cm-2sec-l in the Ford Nuclear Reactor at the University of Michigan. 53 Proton bombardments of natural antimony metal, or of 80013, were used to obtain the 119Te and 117Te activities from the 121’123Sb (p,Xn) reaction. Various proton energies from 26 to 52 MeV were used. The primary activities 117Te 118 121 120 produced were Te, 119Te, 122 Te, St, and Sb. the optimum proton energy for producing 119Te was 118 found to be approximately 3A MeV. Above 39 MeV, the Te contaminant was also produced in significant quantities, 121Te to 119Te while at lower energies the ratio of increased. While sufficient amounts of 117Te could be produced at 48 MeV, the relative yield of 117Te to ll9Te approximately doubled when the proton energy was raised to 52 MeV. The proton beams were produced with the MSU cyclotron. The tellurium activities were chemically extracted from the target material by precipitation with 802 gas. The metal target was dissolved in aqua regia and converted to the chloride form by boiling the solution to dryness to remove any nitrates. The residue was dissolved in 3N HCl, and hydroxylamine hydrochloride was added. The solution was placed in a warm water bath, and SO2 gas was bubbled through it to precipitate tellurium metal (32). In cases where the target material was Sb 013, the chloride form was obtained directly by dissolving the target in HCl. Because of the more rapid chemical separation, 117 the SbCl3 targets were used to obtain the 1.1 hour Te 5A activity from short (a few minutes) bombardments. For longer bombardments this form of target was unsatisfactory because of its low melting point and deliquescence. The l29m+gTe activity was allowed to stand until traces of the 131 I had disappeared, eliminating the need for confining the iodine vapors. No chemistry was attempted on the 12%Te activity. In the case of 119Te and 117Te, it was necessary to add tellurium carrier in order to remove the microscopic amount of tellurium from the many milligrams of antimony. CHAPTER III EXPERIMENTAL RESULTS 3.1. Summary of Previous Studies on the Activities of 117Te, 119Te and 129Te Prior to the development of high resolution Ge(Li) 117 119 detector systems, the decay schemes of Te and 129 Te, Te had been studied by several investigators (32-A3). During the study performed in this laboratory, results 129Te were of several other investigations of 119Te and published (AA-A9). Although most of these latter studies utilized Ge(Li) detectors, there were many points of disagreement among the individual decay schemes. Hence it was felt that a continuation of the present study was Justified. Brief summaries of the results obtained by various groups are presented in Tables 2, 3, and A. For brevity, while several similar reports are available from different investigators, only one or two of these, representative of a given technique or type of experiment, are listed. Major steps in the evolution of the energy level schemes of 119Sb and 129I are shown in Figures 6 and 7, respectively. 55 56 Table 2._-Past studies of the decay of 129 Te, Levels (keV) or Techniques Quantities other Principal Investigators Used Measured .Results 1. Graves, magnetic lens By, I , 27, 502, 720, 1150 Mitchell (Al) spectrometer, yy-COInC scintillation 8 -coinc detectors 2. Ramayya, scintillation By, I , 27, 280, A92, 570 Yoshizawa, detectors YY-coinc 710, 8A0, 10A5, 1127 Mitchell (A2) BY-coinc 1255, 1A00 3. Devare, scintillation By, Iy, 27, 275, (350 or 755), Devare (A3) detectors, YY-,BY-coinc A82, 550, 695, 810, B-spectrometer B-shapes 830, 1105, 1235, 1385 6T Of Y28kev 1u15 Present Investigations Begin A. Bornemeier, Ge(Li) detector, Hy, 1y, Potnis, scintillation YY-coinca Ellsworth, detectors Mandeville (A6) 5. Gupta, scintillation EY,YY-Coinc Saha (A?) detectors YY (0)a 6. Hurley,- Ge(Li) counter, Ev: 1., Mathiesen (A8) scintillation vv-Coinca counters . 2 7. Bemis, iron core double Ece,xa,6 Fransson (A9) focussing of 28 keV electron transition spectrometer 8. Walters, Ge(Li) detector, Hy, ly, Gordon (50) scintillation _ d,e counter coinc e 9. Eastwood, Ge(Li) detector RY, IY Witzke, ‘ Walker (52) 27, 277, A82, 550, 750, A97, 837, 1065, 1112, 1222, 1385; Identify several new transitions b 27, 278, 3A3, “87, 557. 697, 730, 831, 8A6, 1022, 1077, 1083, 1112, 1262, 1378, 1AOA, 1u27 C 28, 278, A87, 560, 696, 730, 769, 830, 8A5, 1050, 1111, 1260, 1291, 1u02 f aCoincidence counting performed with NaI(Tl) detectors only. b scheme proposed by Devare and Devare, reference A3. cMeasurements confined to properties of d combination. Coincidence counting performed with Ge( Interpretation of angular correlation data based on decay 28 keV state. Li)-NaI(Tl) detector eResults in very good agreement with our investigation. fDid not publish a decay scheme. 5'7 Table 3.-—Studies of the Levels in 1198b. Techniques and Quantities Energy Levels (keV) or Investigators Apparatus Measured Other Principal Results 1. Pink, magnetic a , I , 270, 6A8, 1220, 1370 Andersson, Spectrometers, yi—coinc, 1390, 1760, 2360 Kantele (32) scintillation Tl/3 counters L 2. Gupta, scintillation EY, I 270, 6A5, 1220, 1370 Pramilla, counters yy-coinc 1760, (2150), 2220, Raghavan (36) 2290, 2370 3. Kantele, scintillation E , 271, 6A5, 702, 105A Fink (37) counters Y 1221, 137A, 1755, (2130), 2205, 2291, 2365 A. Svedberg, magnetic , Ece’ a Andersson (38) spectrometer, atotal’ y ' scintillation ‘ counters Present Investigations Begin 5. Ramayya (39) scintillation yy (8) b counters 6. Singru, Ge(Li) and 8,, 1,, E_p, 270, 10A8, 1212, 1365 Devare, scintillation 1“,,yy (a); 2281, 2292, 23u9, 2365 11 — c- Devare (4‘) ,2 double yy-delay focussing spectrometer 0,, oLC 7. Graeffe, Ge(Li), 31(11) 8,, 1,,yy- 270, 6AA, 700, 10u8 Hoffman, and scintillations coinc,yy (8) 1213, 1250, 1338, 1366 Sarantites (A5) counters aw, 61+Md 1A07, 1A13, 1387, 1750 “ ‘ ‘ 1822, 2129, 2226, 2278 228A, 23608 Q 3 r x 8. Bassani llen (JHe,d) reactions Q—values 208, 60A, 608, 1315, et a1. (5A) 1370, 1808, 2118, 226A 23A6, 2702, 2776 1180 3 . s 9. Ishimatsu on ( He,d) reactions Q—values 270, 660, 710, 1370, et a1. (55) 1A90 10 B 118 3 . a . arnes Sn ( He,d) reactions Q-values 201, (385), 635, 695, et al. (56) 1335, 1u60, 16A0, 1830, 1950, 2075, 2215, 2280, 2355, 25A5 aAssign Spins Reference 37. bReport includes study of angular correlations only. to some levels in decay scheme proposed by Kantele and Fink, CCoincidence counting performed with Scintillation detectors only. d Coincidence counting performed with Ge(Li)—NaI(Tl) detector combination. eDecay Scheme in very good agreement with that proposed in our investigation. 58 .ofiomafim>m poc oEocom zmooo MQOHomoHHozo msmcflefiaopmm . a ammmm mmmm momm mesa ommm .oemm .Hmea .osma .mmma Ammo .wm1mm .smma .Hsm .mms .omm nosan>1a ncoaooson Ae.ozmv eweS noccem .e .ommm .owwm .oaem .ommm .oH:m .owmm .oamm .ozam .oama .omsa .osza .omma Ammo .He no .omma .omm .oms .omm nosae>1g ncoanonmc Ac.ommv cmflH snSnEaan .m ssmm .msam .ost .mssa Asmv .Hn mm mmMH .mflm .oom .omm moSHm>IG m91MLummn Anammmv cmoHH Hemmmmm .: \H m msmuCSOO Azmv Eflma cessafl snowman m a .+ m coacsaaaecaon censocsm .m cfiwom mc womauemm>cw ozomopm whopcsoo +mm coacsaaaccflon Ammv manages comm > > .popoEospooom .COmmsooc< .osmm .omsa .ommfl .mas . 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(J "j 73') C‘ F~"fi"-: 2):} F4 Q) IX?) -'—1 3;; H C.) u H a +3 LL. {1 r; H ‘h J I .1} 0,) :- m f L 9‘ r~~~ f‘~ .13 “I“ JW m ~ \5) rv‘ r‘x m1 r—4 “I ‘0 :1 (q r—I r—4 ~.; 5» I'M A r» :7 -3\ «I L n o o o a u o o o n O I n n i ' I a ' I O I o I ‘ (1. 4“ 1?, Q 33 ,a r‘vwx :-~ m D :r «\J 13 (7x r—1 (7\ x: h— 3“: r—I r—< 7x r" {—4 r-4 Cl :3 n; (x; C) ‘- 3W P—Cx) :3 .;‘. r ' I \ "q f~~- :‘N m 1 L; C H "7 if 1? (“J I? I: r-‘ V‘ -3 - I» u! H N m N \I “Y\ r :r n .\ .o \o '0 h t\~ was a: co gp ox —\ :2 H , .' r, m a. H .-—< H r-4 H .——< ,—-4 1.0, ) or the very weak lines. ,1 , except jReference Uh. .1 ( for gamma rays of relative intensity Kev, W c Reference AB. OJ estimated as are 193 o ‘J ensi O in values are p v” c l ’h'. “1"!" . relatr in :ties ncertair < v .I hIouolet. fl and are 67 NaI(Tl) detector. Contributions from II x-rays from conversion of the 150 keV line in 131 I were much reduced by the time lapse of at least two half lives of 1318Te prior to measurements. Calibration points were obtained from x-rays present in the decay of 137Cs, long, and 113Sn.‘ The energy obtained was 27.7 i 0.2 keV, in good agreement with the value 27.78 i 0.05 keV obtained in recent conversion-electron studies (H9). With the intensities of the 662 keV gamma ray and 32- keV x-ray of 137mBa as reference points, and using “K of 0.089 for the 662 keV transition (57), and correcting for fluorescent yield, a y-ray intensity of about 185, relative to 100 for the N60-keV line, was obtained. Using 5.23 for the total conversion coefficient (H9), a value of approximately 1150 was obtained for the total relative transition intensity of the 27.7 keV transition. 3.2.l.B.--Gamma1gamma Coincidence Studies-—Initial coincidence counting was done with a source taped directly to the Ge(Li) detector package which was immersed in liquid nitrogen. A 7.6 cm X 7.6 cm NaI(Tl) crystal was positioned outside the dewar and was used as the gating detector. Because of the small size (=1 cm3) of the Ge(Li) crystal, count rates were very low and experiments often had to be continued for several days. 68 Some results of the coincidence experiments are shown in Figures 9 through 11. A summary of all the coincidence data is given in Table 6. It should be noted that gamma rays of 279 and 393 keV were shown to be doublets by coincidence experiments. Pulses from the Ge(Li) detector that were in coincidence with the desired pulses in the NaI(Tl) detector were stored in the memory of the analyzer. The good resolution of the response of the Ge(Li) detector makes this technique valuable in spite of the low efficiency of the Ge(Li) counter. The utility of such studies is well illustrated in the study of coincidences between gamma rays in the 500- and in the BOO-keV regions. Reference to Figure 8 will show two y rays in the 500-keV region, 532 and 557 keV, and four y rays in the 800—keV region, 802, 817, 833, and 8&5 keV. Earlier studies had indicated coincidences between these two regions (u2—u8) where it was not possible to determine exactly which y rays were in coincidence. In Figure 9, spectrum C where the Ge(Li) spectrum in coincidence with the BOO-keV region is shown, major coincident y rays are clearly seen at 251, 278, and 557 keV. This indicates that the 557- (but not the 532-keV) y ray is in coincidence with one or more y rays in the 800-keV region. In Figure 9, spectrum B where the Ge(Li) spectrum obtained in coincidence with the BOO-keV region is shown, the two peaks at 817 and 895 keV stand out as major coincidences. Thus, the two HF- COUNTS (ARBITRARY UNITS) '0. I 8 I r 4 : _ a : ._,.. 9 " '2°'*'2""To SINGLES . 1 ‘JK o . = ' ,\‘K In 2 " . .1 2 a 1 _ _ M_fi“’!’\, . \ s 5 — '0 r ._ c - ' a - I 1." I [I s : . ‘tfifl‘l -~[ [ : ,. S '_ o -I _ 0 2 . I . '04 a. comoum. 535-600 KEV \, o . _ E . 2 2 at 5 --'..- ' N N v ' ‘ . , r~ 3"." " \- ' \_. d‘ -_ 8 3 ' . p 4 .: .~:~\’[‘s} ' "J - a -< - ’-"'-:' ~'.. 8 .-‘ " '— ‘ . ' - -- -"L‘J'jk ”r" "I J" 4 -- --- . . u.’- n c. comc. with 805-895 KEV 2‘ g 3 O .-_ . IO - n 0 , - : N Z ,. : ' 1": -’| n _- - " . _¢ 1 tn; Ij‘ f .- - ' - - ‘-’ «I _ _ - _ ,- L25. ,1". -' -'_ ,- _ - ~ '. I ‘3- '- I _ r~ < ,_ T _ DO _ -. - 'EAEW- : - 0;: . - . - 2 - '- -- . _ _ - - . -- ~ 1‘ - - = 0 I: o. comc. with sac-Iozs KEV “' I _ ’1' - . :- a", . I'."‘-_‘ - - : ' -’ x s 2 I - r -- . ‘ ' 2.; ~ N - - - i _ .' ' \ [I i ' ' J_- __-. -‘ - - .- ‘4‘! . . .' L i. _ 3. ,n. Io':' ' "Zr-“"3“ ' '. IF '- ' 1 b r. 9 — : .9 _"x‘_: -_ d f '00 l ' '.. 300 ‘600 900 ENERGY. keV Fig. 9 Ge(Li) spectra of 129m+gTe in coincidence with three regions of the spectrum seen by a 7.6 x 7.6 cm NaI(Tl) detector. A 1 cm3 Ge(Li) detector was used. A_singles spectrum is shown for reference. The coincident spectra have been gain shifted by the computer to allow an easier comparison. 7O 00¢ A .houoopmo mzasccm AHBVHmz on» Some >mx Oman 0» unaccoammphoo mmmaso nuH3.mocmoaocaoo :fi mBu+EmmH mo Esauomam “Havoc < OH .mHm mwmzfiz szz3. On. A 4.2240 1 >24 It; .0260 p p P p l SiNnOO COUNTS (ARBITRARY UNITS) 71 r’am m 1 ‘ , 38 § «'3 $11 A SINGLES “29”” To . 1m * "\"v‘jij. 1 S ‘D' ' .‘. '3 ' 1' 031: 6 “an ~1fl ”1 104* V\. 1 1 110 m 1. r \ .‘..” 1,31 3.... N z I, :2 0 18“ 11' ‘ 4 “:1. " .‘ ' 0 JR. g 1 1 N g '\w\ 21 _ 8: 9 5 7'1... wnl 'V 'an . 101—"WI.“ I‘m 1.. to" 1 1 o ' \ ,' «o - 100° .'. 7 <7- \,' F .1 .'f’ . ' .— - ”/1 ‘."...'1l"1l1 I 1 : :’ '._ 0 8 as v ' 11‘! T '. :8 ‘1“ E 1 8 come WITH 28 K v N N ° 1' 11 a - - ° ' x 11,111 '- 8 <3 .8 J :1 1 4 J " n 1 '11 1 n 1 ‘ 0— ‘ ‘0 0 .. . '01 1' 8 a "1:1- ,1; . a * \n‘ 1 1 IV . . 1‘. \1 1 ,1 N (3 + \‘._ I 1 . .. .. ' I. '0 . “W" 1 .1- N h . on -I g r wing 10 ' 1a ;1 0 ‘. “3 11 c . '0 N . . .1 I] 31" N 1 ts 8 . ‘ - 1! 11 1-1 to — . .. . .1 I61 “W 113 fig g1um..‘U1. — “ "J , ‘. 1:111} .‘m g ”IRA" .1 1 J1 .11" 1.."-.- 1.... ‘Ksy'vh . . .'.._. ~ 1 , N 1 ". g g -' __ 2 m ' 1 E w a 1 l -. '0 :1 11 ' 1 '1-1! 1' 1 1 _ ' 11' 1'1 N g 113 3 1 p1 - h l 1 :1 I; IO?T ' 1 1:1 it 0 ! 1 {P 1" ‘ 0 1 ‘1 | < 5 5 L 4+ __j ICC 200 300 400 CHANNEL NUMBER +17 - Fig. 11 A spectrum of 129m ”Te in coincidence with the 28 keV gamma ray. Because only about 5% of the counts in the gate (correspondinp to the 28 keV gamma rav and to x-rays) are in coincidence with other tran- sitions, a large contribution to the snectrum arises from chance coincidences. The coincidence oeaks can be identified by comparinr their relative heights in the coincidence and sinnles spectra. A 7 cm3 Ge(Li) detector and a 2.5 x 3.8 cm NaI(Tl) crystal with a thin Be window were used. Table 6.--Summary of Coincidence Results for A. Differential gates l29m+gTe Coincident with Energy In— Photopeaks Coincident Comptons & Con- terval in in gatea with peaks taminants in Gate (keV) (keV) in gate Gate 910-1025 981, 1022 250, 279 657b 805-895 802, 817 250, 279, 557 657b 833, 8H5 650-730c 62M, 672, 696 3M3, M60, 672 250, 279, 557 730, 7M1 729 535-600 532, 557, 62M M60, 817, 8M5 250, 279, 557 M2o-sooc M60, M88 3M3, 62M 557, M60 260-280C 250, 279, 281 135d, 209, 250 557, 62M 279, 281 28e 208, 250, 281 3M3f, M60, 532f, 557f, 7M1, 802, 817, 833%, 982, 1022, 108M, 1232, 1261 B. Integral gates Energy in Gate Coincident Gamma Rays (keV) 150 250, 279, 281, 3M3, M60, 557, 62M, 657b,672, 73o, 7M1, 817, 833, 8M5, 982 300c 208, 250, 279, 3M3, M60, M88, 557, 62M, 657b 672, 730, 7M1, 817, 8M5, 885b, 937b 77oC 250, 279, 657b, 885b, 937b aIncluding photopeaks only bDue to 110m CSpectra not shown. d 8Includes 28 keV gamma ray Ag contaminant. and x-rays. fWeak evidence due to poor statistics. partially inside gate. Presumably backseatter of 279 keV doublet. 73 experiments, taken together, serve to establish the 557- keV y ray as being coincident with the y rays at 817 and 8MB keV. It is possible, therefore, to overcome the inability to resolve closely lying peaks in the gating detector and to determine exactly which peak or peaks are causing coincidences to be observed using the above approach to the analysis of the data. In most of the coincidence spectra shown there are a number of additional peaks resulting from chance coincidences and from real coincidences with Compton background events. The latter can be treated quantitatively by a knowledge of the width and position of the gate and of the y rays coincident with the higher energy y rays whose Compton events fall in the gate. A good example of this is seen in Figure 9, spectrum B, where the 557- keV peak appears in coincident with 535- to 600-keV area. Three explanations of this observation are possible: (a) the 557-keV y ray may be in true coincidence with the 532—keV line; (b) the 557-keV photopeak may arise solely from random coincidences; and (c) it may be in true coincidence with the 817- and 8u5-keV transitions both of which contribute to the Compton events falling in the gate. The first possibility is eliminated as a 532-557 cascade, as it would require that the 532-keV y ray be present with at least as great an intensity as the 557-keV y ray. Case (b) is ruled out 74 as the ratio of peak areas 557/696 would have to be the same as in the singles spectrum; the peak at 696-keV, which is essentially absent in Figure 9, arises entirely from random events as the 696-keV transition has not been observed in any coincidence spectra. Thus, we are left with case (c), that the photopeak at 557-keV arises from true coincidences with Compton events from the 817- and BUS-keV y rays. In Figure 10 is shown the "any-coincidence" Ge(Li) spectrum which is the spectrum that is coincident with any events that deposit more than 150 keV in the NaI(Tl) detector. This spectrum serves two important functions. First, it indicates which y rays are involved in cascades and, thus, must be properly placed in the decay scheme to obtain correct intensity balance. Second, and perhaps more important, it shows which y rays are not involved in cascades. Those y rays whose peaks do not occur here, or in Figure 11 which shows coincidences with the 28—keV ' 7, almost certainly lead to the ground state. Furthermore, those whose peaks appear in Figure 11 but not in the any-coincidence spectrum must terminate at the 28-keV level. Notable absences from the any-coincidence spectrum are y rays of energies 532, 696, 802, 1022, 1050, 108M, 1111, 1232, 1261 and lUO2 keV. 75 3.2.l.C.--The proposed decay schemes--Transitions at 271, 560, and 702 keV were observed at M.I.T. by Walters ££+2£, (50,51),using a higher resolution system. In our spectra, the 702 keV line could not be resolved from the very intense 696 keV gamma ray. The other two lines, if real, are present in the decay of 1298Te, and 129mTe. were masked in our spectra by the presence of The 271, 560, and 702 keV lines are placed in our decay schemes (shown here) as a part of a Joint publication 129Te with the M.I.T. group, (51). on the decay of It should be emphasized that the paper was a Joint report on independent investigations, with collaborations only on the final interpretations of the final results. 129Te isomers The proposed decay schemes of the are shown in Figure 12. It is well known that the ground state of 1291 has a spin and parity 7/2+ and the first excited state, at 28 keV, has Jn = 5/2+ (15). The observation of several pairs of y rays separated in energy by about 28 keV suggests that each pair results from the decay of an excited state to these lowest two levels. For all such pairs, except the 137M- and 1902- keV pair, coincidence data are available (See Figure 11) that confirm the existence of a level at an energy equal to that of the high energy member of the pair. Namely, for levels at 278, 987, 560, 730, 769, 830, 8M5, 1050, 1111, and 1260 keV, y rays of energies 251, M60, 70 min l93. 0.2%. 8.2 76 (00“) ("£2 0\ I98. 0.0I%, 6.7 229. 0.05%.62 377. I 2%. 5 5 659.01%. 7.! 72QS0.04%.28. 929. 0.2%, 7.7 IOOZ, IO%. 6.! IZIO. 0.8%. 7.5 IOGI. 88%. 5.8 (GI) [.12 ' N - o' _' -00 2 :. .2- 3.... - n N Vii : o o 09'? o: ‘5 ‘5. 0°.”. 0‘ o‘ o ’00 v n 800: 3 n r~ coo - Proposed decay schemes of 129mTe and 129gTe. The dashed lines represent transitions which were ob- served at MIT (refs. 50 and 51) but could not be reliably identified in our investigation. They are included because of a joint MSU-MIT publication. 53 77 532, 702, 7M1, 802, 817, 1022, 1084, and 1232 keV, respectively, have been observed in coincidence with the 28-keV y ray. Furthermore, transitions depopulating the levels at 278, M87, 730, 769, and 8&5 keV have been observed to be in coincidence with the 833- and 982-, 343- and 624-, 672—, 343—, and 557-keV transitions, respectively, giving further support for the placement of levels at 830, 1111, 1260, and lu02 keV. The relatively high intensity of the l261-keV doublet in the spectrum in coincidence with the 28-keV transition suggests a level at 1292 keV. The low intensity of the 1374- and 1&02-keV transitions makes coincidence experiments with these transitions impractical at present and so both of these gamma rays are placed as depopulating the 1u02— keV level on the basis of energy sums and the above mentioned cascades that have been observed. The large' intensity of the 696-keV y ray in the 129m+gTe singles spectrum, in conjunction with its absence from all coincidence spectra, indicates the existence of a level at 696 keV. The placement of a level at 769 keV has been made on the basis of intensity data and the presence of a very weak y ray at 769 keV. There is little doubt that the 7&1- and 3U3-keV y rays are in coincidence and represent a cascade from the 1111— keV level to the 78 28-keV level. In the decay of 129m Te, the intensity of the 7Hl—keV line is greater than that of the 3H3— keV y ray by an amount sufficient to indicate independent beta decay to a level at 769 keV. The presence of a weak 769-keV y ray serves to confirm this assignment. In the decay of 129gTe, the intensities of the 7Ul- and 3u3-keV y rays are equal within the limits of the experimental error. If we make the reasonable assumtion that there is only one 7Ul-keV y ray, then there is little doubt about the order of emission of the 3M3- and 7ul—keV y rays in the decay of the llll-keV level. For a level to exist at 371 keV, the existence of two 7ul-keV y rays, whose energy separation is less than 1 keV, must be postulated. No significant shift in the centroid of the 7H1 keV peak was observed in Spectra obtained from 129gTe from those obtained from 129m+gTe. The Q values for the 8 groups shown in Figure 12 were derived from the endpoint energy for the transition from 129mTe to the 1291 ground state, 1595 keV, measured by Devare and Devare (U3) and the y-ray energies of this work. The intensities of the 8 groups and the I.T. 129m (isomerictransition) branching fractions for Te were determined from the net flow of y-ray intensities out of each level and the ratio of intensities of the 1595-keV B group as determined by Devare and Devare (U3). The 129m resulting value for the fraction of Te decay by I.T., 79 72%, is in reasonable agreement with previous values of 64% (H3) and 68% (58). Log ft values were determined from the partial half lives and endpoint energies of the various beta groups by use of Moszkowski's nomogram (59). 3.2.2. Decay Schemes of 119gTe and 1lnge 3.2.2.A.--Gamma Ray Singles Spectra--In order that activities decaying with different half lives could be properly identified, singles spectra were recorded periodically as the sources aged. Gamma rays were assigned to the decay of 119gTe or “.7 day 11nge from measurements of their intensities, relative to the 6ND and 1213 keV lines, in successive singles runs. A total of twelve transitions are tentatively assigned to 119gTe and twenty to llnge. The singles spectrum and expanded segments of singles spectra are shown in Figures 13 and an through er. Lists of the gamma rays and relative intensities measured in this and other investigations are given in Tables 7 and 8. Because of the longer halflives (17 day and 159 day), identification of transitions belonging to the 121Te isomeric impurities presented relatively little difficulty. A spectrum of 121 119m Te, recorded after many halflives of Te, is displayed in Figure 15. The energies and relative intensities of the gamma rays present, including the very weak 910 and 988 keV lines, are in very good agreement with 80 I l I l 8 .5— ._”0 96802 —.———-—=—-'-————":—'3.—___ 92:02 --=——-——_—_ — a..." "I‘;’ it ’2: E .. C) 1p— 3 4r“) 2}- s (69023984191 4% w 15 E 3‘ OIEI '3; SZI ‘81 (318“) SZZI ,gzxL—T; 92:2: 2:?— L‘Sillx. , _.-.--* O 4 "1:20 55ii\ '2'} __.o 8080: ”960M517 ID . revo: ----—';:' B'ZIOI __ -5“ 61.6 .J"”" 91.6 £296 1 tZIG --~’ ”.9 4— (31'2” EL; I‘m—7;:T... ——q»§ n9 _. ____,) (01.30809 ‘ -——) (‘l|z')0997 £012 —u-~-=--——-:jj . m_=:—--—' ( 1 male ._1 ____L’_9L_._..~ 9‘29: '—‘ . : : 1 ‘3 C> o» C) c> o C) C) C) <3 C) '- 0 O o o - O O o _ O o .. 9 — (3.1.an AHVHLIGUV) SlNflOO NUMBER CHANNEL 13 Singles spectrum of llnge recorded with a 3 cm3 Fig. Ge(Li) detector. LOO 0.0 00 COUNTS Fig. :‘ :ooooo-— 7 l” 81 -_-. |52.8 _. -——-.——-. 2.2mifimlfifl- O '0 fifi~ o udooo-— 3%. 7 250 500 CHANNEL NUMBER Segments of the Ge(Li) spectrum of llgm+ETe shown on expanded scales. Transitions belonging to llQ"Te are indicated bv an asterisk (*). a) 120 to 250 keV region, b) 500 to 800 keV region, c) 900 keV region, d) 900 to 1800 keV region, e) high energv region. 82 IOOOOOO IOOOOO"- COUNTS IOOOO"- l2l Te) 699.6 it 0‘. O . ‘=573 ( 5:: ' E: 644.l .. .__>. \ .'.-.‘— § 0" . o . . . 0 o . o . C o . . a \. .———— . O l '2- 727 (D.E.I749) n» :ooo Fig. 14b zoo CHANNEL NUMBER 360' COUNTS 83 40000 9|2.4 36000"— ..b. 942.3 \ azooow— . . *%L£“V ' : \. x L. zsooow— . / 24ooo£mhwymavggmyw 20000 i 800 900 CHANNEL NUMBER. Fig. iuo 814 ' 1 l00 l T * I’GVU =\._. 3.” 2...: .‘. . 8'2Iv: rig. ,_ 9'992: g _fi 3 IL'BEEI <° 2". (91.3”) GZZI 5 92:2: €:_‘ ‘: :8'91H «:3 1:. [92H :71? <- ' ' I <" vsso: s: ' o: 5:? *— (6802'3'0)9'1.so: =7...- _. I'BbOI at?“ 92:0: .5— 2’ 1.1.6 c, 22:76 «'5 9 <5 '¢.'l6g I l 8 8 8 O o o 8 ° - " SanOO Fig. lad .1 600 500 CHANNEL NUMBER 400 85 _ — d amom +0st 88 int”. — 1 d _‘ .0'. O o 09 . I0000 950 750 ‘ CHANNEL NUMBER Fig. er 86 Table 7.-—Energies and Relative Intensities of Gamma Rays Observed in the Decay of ll9mTe. Present Work Kantele and Finkc Graeffe et a1.d Energy Uncertaintya iiizb Energy 7:8: Energy 78%: 117 2.0 <0.5 115.5 0.7 152.8 0.5 100 153.0 9“ 153.0 99 16“.1 1.0 1.7 163.9 6 163.9 1.7 270.3 (3.3 “2 270.6 38 270.6 39 “00 760-780 871 1.0 50.6 800 872.0 0.“ 912.“ 0.6 9.7 917 6 912.“ 10.2 9“2.3 0.6 6.3 9“6 9.5 9“2.1 5.9 976 1.5 “.5 976.“ 3.9 979 1.5 “.5 98“ 12 979.0 “.5 1012.8 1.0 2.7 1012.9 3.9 10“8.1 0.7 “.7 105“ 8 10“8.3 “.7 1080.8 0.9 2.8 1081.0 2.3 1095.“ 0.5 3.0 1099 7 1096.0 3.“ 1136.7 0.9 11.5 11“0 10 1136.0 11.7 1212.6 0.5 100 1221 100 1212.7 100 12“9 2.0 0.3 12“9.6 0.2 1311 2.0 50.3 1311.0 0.2 1365.8 0.7 1.7 137“ 2.2 1365.8 2.0 1500 <0.“ 1760-1780 <0.“ 1900 <0.“ 2012.5 0.7 0.“ 2013.0 0.5 2089.“ 0.7 7.3 209“ 7.3 2089.7 6.2 2350 <0.05 2570 <0.03 mean values obtained from many measurements. bGamma intensities only. The uncertainties are estimated to be 110% for the prominent lines. 0Reference 37. dReference “5. aUncertainties in energies are rms deviations from the 87 Table 8.--Energies and Relative Intensities of Gamma Rays Observed in the Decay of ll9sTe. Present Work Kantele and Finke Graeffe et al.d Energy Uncertaintya Rel. Rel. Energy Rel. (keV) (keV) Int.b Energy Int. (keV) Int. 270.6 0.2 . 373.7 0.2 6““.1 0.3 100 6“5 100 6““.3 100 699.6 0.5 12 702 13 700.0 11.5 68“e 1.5 0.1 7686 1.5 0.1 788e 1.5 0.2 787.3 0.2 8“3e 1.5 0.3 8“3.2 0.3 1105.6 0.7 1.0 1105.5 0.8 1120.0 0.6 0.6 1120.9 0.2 1177.8 1.1 1.0 1177.2 1.0 1338.7 0.7 0.3 1338.5 0.2 l“l2.8 0.“ 1.2 1“l3.2 1.1 l7“9.1 0.5 “.8 1755 “.2 17“9.3 “.“ aUncertainties in energies are based on rms deviations from mean value. bGamma intensities only. Uncertainties in relative intensities are estimated to be :10% for the prominent lines. 0 Reference 37. d Reference “5. eEnergy and relative intensity obtained from coincidence data. 88 Ge(Li) detector after the 119mTe had decayed away. : l .1 “! a: 3 SINGLES 'z'Te 3'- ; IOSRA B I g — ‘ :_- A 1. - “\JLVJ g . 8 $2 :04.- .,_ f _ ‘2 a \2 : - ¢ > ' I n: _ JL: : _ E 1 : *- :o3— V 3 _ E ' 2 . m .— s - . - \ a) - *2 “we“... - D |02_— °’ , _ O _ K g _ O 8 _ _ 'ilfi _ 1 IO :— g‘qf. —_ _ 'a l I l 250 500 750 CHANNEL NUMBER Fig. 15 Singles Spectrum of 121Te, recorded with a 3 cm3 89 results obtained by Auble et al. (9) using only scintillation detectors. In our investigation of the 119 Te spectra, no evidence was fownd for gamma rays in the 1500-1900 keV region that were stronger than 0.3% of the 1213 keV line. Also, upper limits for intensities of the possible 2350 and 2570 keV gammas can be reduced by at least a factor of three from the values which had been reported by other investigations (37). A sum peak of 2360 keV was, however, observed with the 12 cm3 and with the 7 cm3 Ge(Li) detectors and a typical one is shown in Figure l“e. Relative intensities of the 68“, 768, 788 and 8“3 keV gamma rays in 119gTe were obtained from coincidence experiments since these weak transitions are masked by Compton backgrounds in singles spectra. A very weak gamma ray of 1260 keV was present in some of the singles spectra. It did not, however, decay with a half-life 119m that was characteristic of the Te and 119%Te and is therefore attributed to another activity. 3.2.2.B.—-Gamma-gamma Coincidence StudieS—-Gamma- gamma coincidence experiments were performed using a 7.6 X 7.6 cm NaI(Tl) detector as the gating crystal, while spectra taken with one of the Ge(Li) counters were displayed on the 102“ channel analyser. The 1 MeV 119m region of the gamma ray Spectrum of Te was scanned with the NaI(Tl) Spectrometer in a series of 100-200 keV "a 90 steps, starting at 1370 and ending at 900 keV. In other coincidence experiments, the gates were set on the 153- 16“ and 270 keV photopeaks. The results are displayed in Figures 16 and 17, and are summarized in Table 9. Two types of coincidence experiments were performed with the 16 hour 119gTe activity. First, a spectrum was taken in coincidence with an integral gate set above “50 keV. This discriminator setting was chosen to minimize effects of scattering between detectors, which were oriented at 180 degrees in this case. The absence of the 1338, 1“l3, and 17“9 keV gammas from this Spectrum indicates that these are ground state transitions that are directly fed by electron capture. The relative intensities of any possible gamma rays feeding these levels must be assigned to be leSS than 0.1. Second, a Spectrum was taken in coincidence with a region including the 6““ and 700 keV photopeaks. A coincidence between this region and 1100 keV has been previously detected by Sorokin g£_al. (“0) using scintillation counters. Our experiment resolved the 1100 keV region into lines of 1105, 1120 and 1177 keV. Furthermore, weak peaks at 68“, 768, 788 and 8“3 are also present. All of the above gamma rays retained their relative intensities, to within statistical error, in a second Spectrum that was recorded seven hours later. Subsequent experiments, gating on either Side of the 91 7,-— - f 7 17 i '2. '; A SINGLES “9T. ' :- 10 __ l‘ N‘E‘ ; db '0 1 (a a v 0 ar- w-‘1 . {Q A 1, :7 :7 I: g; a \J , l A '2, . ar: e 8~i n -"\~~. {x} '0 3 - A n O m. v ‘ l 8 — r~ . I09...- [I J ‘ g n: i1 8 «r I" ‘1 - \ N r~ - n J 0 "v". '. U ‘ ' ‘ ‘ \r'I \ ‘9 1‘ gt a S g g '.‘.'.‘.\‘»'\-“‘.”'"""“A-,4 '. v .r .\ \." "'6' I") h 1 I '[ .....-..~q'.\. .5 8 H i :' (1 7"" - " -' . I ‘1 9 ' 3 r. I 8 ' a mum I365 - (8:. '2 .‘ J 10 ‘ ‘ ' .-"-"." 1 3’ ””5“” .— ' > 1- : . M. : ~ i r g "\ I I} ‘ .._ 31.. ~ -.I- : ..v '. a \ {\ ‘: I. ‘. ' ._-..' ‘ / ~' ‘ 1: i- \ ‘ .1 a ”A! 1 t .3 k; 11 ':~ 92 5 -. IOL771 Ali " i . ‘ . :- m I ‘ .' l . a ‘ , 7' . o . .. _. I F ‘ . :_ N - I A ' 0",,1 A L, ,.:N: :;:‘.3 .. u) '2 \ 1 F- 6 -— ‘ 2J1 .11 - -:r 2 IO 0 I \AJ :- IO 1 D 1 \ 3i Lax s; 1 L "*- . > : : a - av : 3‘ 1 ' V1“. ~\ ‘ m g 1) .- “ I‘ ~. AM ’ ’1‘ h ’12 . , - - - " o a lo 5 " ' 11]". [l | “V'- f.‘ j 1. :1 .‘- q» '01 1 ' 7 4 an E E 9! ' o.co:~c :o4e-:2:3 - 3 a: 7. a, . ‘ ‘ O .‘.» , ~._ PU: » ‘1 z “ /"~ .1.“ :3 1 Z 7, I . , in“, .,, v. F . .._. r m' . Z 4 8 . ..\ H F e -. : : o :o :3. , :- 7 a .. s. ~> .r- .‘1 ‘1‘.“ ’1 . > ' k . ' ..I ‘ l: . 3. I 'v \ 1 1:1 1‘ ii ‘-. E (.OINC 9424048 ' ‘ 56 -’. ..V r—. ' :- : - o \'-‘4‘-.‘-.‘. :~ - 1. .' ‘ .. - , 7 3 . é - F \- “.'..n '31-. ' '-._ . .‘ .1' . l- 1- . N m ’3’. X ‘ . . 'O l N" - r. ‘-..-~ - w‘w‘.‘ ~ ‘ “wax a 1 - 1 '“' . ‘ A. ' rm 1' 1 ll. 7' ! 15. --.'J 1 a L 1‘ ' u: m .' I. F (gomc 9:2- 942 .92 :I fly! | lash. 'l' I 2 3 “7" IO " ‘ '~. 7..., -_ 2 . .\ A -'" E if 1 r) V 1 §j g 4 1‘ 71‘ I ,7 I? , 1 I.» ‘ .‘ :o ‘ : _ __ 1: :1 ‘ x 1 1 t . 0 .. . :o —- . ~ — . :uu‘ (UL) .500 400 C i I ANNE L Nl LUBE. R Gamma ray Spectra of linge in coincidence with various segments of the 900-l“00 keV region. These spectra were taken with a 3 cm3 Ge(Li) detector and a 7.6 cm x 7.6 cm NaI(Tl) c tal. A singles spectrum is given for reference. The spectra have been ar- bitrarily displaced vertically for ease of presenta- tion. The energy scales have been adjusted to be equal with the MSU CDC3600 computer. VH7“ LJQ COUNTS1ARBHRARY1HMTS) IO 92 . f 1 1 I .5 m_f% 2 g i Q- N m “LNH' 1' ”9 1 1 11 _ p A SINGLE 5 Te '1 11 I; F) In “5.1.1 1 . a M‘. :l ' Q ‘- " O 9.- " ‘ 0g 3 _, 1 11‘-\ 1 ' N N” g I: 1 Wk,“ [1 6'5 33:00" 3 '1 9 ‘11 1 9 41 A ,1 ' :16 ! I \19 r 1 &* 'W'1 J 8 1 .1 1' a) . 1 o '1 1' 1 to o a ‘ 1 a 8. come WITH 1 . m N 0 <1 7 N -._ I Q U o 0 1 | . 153, 164 ' 1.. . Ui N 1 1 1 ' V 1» 1' '2 In 11 -’ :11 ‘3 1: N1 1 2.11.” ,2,“ _. r" 1 _J_ '+ae: s “9’ ‘1 we . ”deuz‘ax ‘ 1-. .'l‘iafis .- 11: 111 11:43." ‘1 n : 1 0 ' N‘ _ '1 1. '\_ Wfi‘rzn _ _ a1 "I ' Q 1, _ 1L "—.’.-rv"“ :,‘-.-.~1 ‘."A‘~.‘.-- ' Amt-.‘d/I-Nh "‘ g ‘ I 8 . I I‘ 0 ., a: 11 .3 :1 1 1 .. 1.: ' 1.13I1 I. 1 i 9 214 a. 0 1: .'. .11 .1" 4} <1 1.. ~61 1 41 ‘ I o. ’ O n 1 1: 9 5 1 1 i p ' 1. 1 C. COINC WITH 270 m. ..-1 2 A ’ «>1 #1 . N g :. . 8; o , = o 4 41— 1' 111-1‘: N N .-. ‘11: 1, “AV :1 g V I» w h . V 0‘ 1" d m was 11 N . 0') vi!) -— 1 . ‘ 11 . .. a :1 ,~. :3 8 .- g v.~\.‘,\ .‘..‘J L f. 4"” 23‘. ' ,‘ _ 1 — ' __ . . 11- °" ‘1”‘\.‘1 ~11 1 9 1 O 1 ~11 :1 1 n N 1 1‘ 1 111 e 3 1 4:— 1». '11 ! 11 ‘ v 1 1 1111': 1 2 ’ 1“ 1 9 E: 3 1 1" . ‘. ’ \' 'nu' ',' 1 1 2 111 '.~ 0 1 v, N 2 ‘ _ .1 —-4\- 1_ . _ fl. _1 h 4» ‘111 1 0 “I 1_ :11 l o 1’ 1 1» I 1»— 1,—4» 4» ‘1 e 1 1 Fig. l7 Gamma ray spectra l ICC 200 CHANNEL NUMBER Te in coincidence with the of 153 and 270 keV regions. this case had a 7 cm3 119m 300 400 crystal was,the same as‘for fig. 16. The Ge(Li) counter used in active volume, while the NaI(Tl) 93 Table 9.—-119mTe Gamma-Gamma Coincidence Relationships. Ge(Li) Spectra Gammas in Coincident Figure Gatea Gammas Coincidence with (keV) (keV) (keV) l6B 1366,.12U9 153, 1013 1213 1213 270 2089 Compton 912 1366, 1213 976 12u9 121 160 1213, 1137 212, 508, 573 chance ( Te) 12u9 153, 912, 1013 1213 270 1137, 2089 Compton 976 12u9 1213 chance 16D 10u8, 1067b 153, 912 1213 1081, 1095 270 1095, 1067 (D.E. 2089) 1137, 1213 2089, 1137 Compton 1098 1081 1081 10MB 16E 912, 942, 976, 979, 153 912, 1213 Compton 1013, 1048 270 976, 2089 Compton 912 1213 Compton 10MB 1081 1213 chance (12u9)c 976 173 270 153, 992, 977 1067, 1095 270 1137, 2013, 2089 270 underlying Comptons 1213 chance 17C 153, 16” 912 153, 16M 9M2, 1213 153 10MB 16“ aIncludes photo peaks only partly within gate. b Double escape peak of 2089 keV gamma. CA later experiment, gating on the 977 keV region, definitely established the 977-1299 and 977-117 keV cascades. The later was confirmed in a triple coincidence experiment. 94 sun—700 keV doublet, revealed the 68k, 768, 843, 1105 and 1177 keV lines to be in coincidence with the sun keV transition, and the 788 and 1120 in coincidence with the 700 keV gamma. These results are shown in Figure 18. Results of triple coincidence experiments with the split NaI(Tl) annulus (26) and a 7 cm3 Ge(Li) detector are shown in Figure 5 and are consistent with other coincidence data and the proposed decay scheme. Spectrum B of Figure 5 shows gamma rays in triple coincidence with simultaneous pulses in the 153 and 1212 keV regions. As can be seen below, the 912 keV gamma ray is the only one in true triple coincidence with both photopeaks. The presence of the other gamma rays can be accounted for by a true coincidence with either gate, plus a chance coincidence, due to the use of a strong source, with the second gate. Similarly, in spectrum C of Figure 5, for which the two gates were set at 270 and 9u0-1150 keV, the 977 keV doublet and the 871 and 117 keV lines are the only true coincidences among the photopeaks. 3.2.2.C.--The Proposed Decay Schemes of 1198Te ll9mTe—-Based on evidences from coincidence data, fiv— and energy sums and relative intensities, consistent decay llnge. schemes can be constructed for both 119gTe and While the placement of the strongest transitions remains, in general, unchanged from previous work (37,38), 95 (ARBITRARY LNTS) COLNTS I Si N V I o A. SINGLES "9M! To , . I I a 0 I. 1 . - I06 -~._,-’ 1 " 7 >.. "‘ ‘ _l : .1 I. '. ~ 'I. I ‘4 '- l“ 4 V "w" .. 9 ‘-1 I ‘ n- "WWMMW’ '. I‘ n 8 n n! H B . .— '.; I. "a : : I) l I F 8 d p '0 *JL I l: W 7 ' F . i' ‘- N F ' _ ' N 1., T . J I 3 g V b ‘ _., 5_. I . «m- .I 0 0 0 I '0 h ‘ ‘ i x”.‘/.'-"'" ‘ IL ‘\ f . . + h .'.: ‘ I‘ ‘l a . cso‘N4C7 OMOT H .‘W‘u‘ :3 ‘.”"\"'\‘_:"'::‘I:".““’VV:..—\Ka‘ \['\./‘\.:_’.g..’.‘ z I! 4 I’ - : . . : i ff '.I } l ' o ' .-\ . I .1 .0 ‘fi-x" ) 1 ’JK. [7‘ ' . .‘. IF? [\ in ‘ ‘ w a.» .. .1 : -~ «I. I; .. ‘ . .~'w.’- u/"Id'lo " i l O . \_. ..L {f 4 .- - . . o . I. - J. — D __ Y. \.’.‘. ‘ If . N . ,-... -.:. 1 fl ‘ ’ n ‘5 ‘-. f ‘ fl 5 ‘3 F . I 9 «,1,. 3| .W. fl ° * aim «IM‘ 1 3"? \1-.- e‘ ‘ - .g \‘- 0’ \- .- ‘, . i I .._ x - a '. _ ”.._"- - v. . . . In A 8 g. . -"'\\ a" . a“ I O ’ ‘ v ‘ '_. ~l- .. .._ . Y - . - 1‘; g; c. come WITH 2 r- ~' “w p.17 =.o g: I I ' x N — ‘ 1 5 6 4 4 n : T I: II I" '18 . ! "I I I 1 I I ' k“, r" ,1 I I ‘fm. r I I. I .\ ' L ‘ I —4 o '4‘ . ' ‘- u .. ‘ .' ”.‘.-1..) 1‘- ._.-.,.'4-‘.. ' .. .i .. . , ‘ . «- v . . 7 so 1 .0 - I “finyvflv I 1 0 -~ . 4 T ' - 1 I v 2 2 In ‘. ' u “i... l a Q o . ‘ . I- u g '2’ , ; a .4 * I g - 0. comc WITH , fl 5,,“- _ . a I :- ,.,. '- .- |O P No " "~-."'I-.4 - 'I .’ . - Pm I~ n ' ' L .l -| w "1 3 g ' . n. 4 ,../ ‘_ w, ‘-_ h p. Q N 7‘ -‘. .. «.'..1‘ ' «A f" 5 a n . 4 h" '~A..,J '. . " o F '2 .f «5” t'.,'.".".f’g : t 9.. »— .. g, f . P 1. ‘ 'o h, [1 > .’y "a: ' ‘1 I I ’— ‘yfl ' . ‘ ' ——< '0 I. ' U\’ 1; ii. ‘ I ‘ _ 'M_‘! ’ I”; " ._ .. - d t . . .. .- J L l Fig. 18 ICC 200 300 400 CHANI‘EL NlMBER Gamma ray spectra in coinciden e with the emu-700 keV region in The 7cm Ge(Li) detector and one half of a 20.3 cm x 20.3 cm NaI(Tl) split annulus crystal were used to record these spectra. Spectra B and C were recorded with the NaI(Tl) detector gated on the high and low sides of the suu-700 keV doublet, respectively. Spectrum D was obtained from an earlier source and shows a segment of the Spectrum in coinci- dence with the 600-750 keV region. i‘f‘r / UTQ . the accommodation of the new gamma rays requires additional levels. The proposed level schemes are shown in Figures 19 and 20, and are in good agreement with results recently obtained by Graeffe et al. (U5). 3.2.2.C.l.--Levels populated in decay of ll9gTe.-- Levels at ouu.1 and 699.6 keV have been proposed previously (37), and are confirmed in our investigations by the high intensities of the ouu.1 and 699.6 keV transitions and the absence of a 6MU—700 keV cascade. Gamma rays of 1105.6, 1120.0, 1176.8, 1338.7, 1&12.8, and 17H9.l keV were found to decay, within experimental error, with the same halflife as the 6AM keV transition. The last three were absent from the "any—coincidence" spectrum, implying levels at 1338.7, and 1Ul2.8 and 17u9.1 keV. As confirmed by coincidence data, the 1&13 and 17u9 keV levels also depopulate to the 6AM keV state via the 768 and 1105 keV transitions, respectively. Additional levels, based on the 6u4-843, 700-788, 6AM- 1177, and 700-1120 keV cascades, are placed at 1987 and 1820 keV. Another level is suggested at 1328 keV by the ouu—68u keV cascade. Positron feeding to the 66M and 700 keV levels was measured to occur in approximately 1% and 0.1% of the decays of 119gTe, reSpectively. No evidence was found for significant beta decay to the ground state of 1198b. 97 I/2+ 0 mm (LO) (0.6) (4.8) (I O) “/2 L3/2) 4310/ 470 0.9% 6.4 ”494/ 540 4.9% 6.! ‘ 'In‘ to NJ“. '1 "'- E §§ 5} 9,219 3 8 / I/Z 312) I48 / BIO 0.6% 7.2 Hz 312) Emil/9 990 m. 7.0 "12,312, I338. 950 0.3% 7.7 l (I/m/ r . ’ :T \nszs) 960 0.I°/. 7.9 0 h- : 'cIm-‘°Io a: «Ihwc'h-Fifiq 1 l I I : A {23 8 I: I: , (I/2.3/z) 1 699.6 / |590 (9.2% e,O.I°/.B+) 6.6 012.3/2 I 644. I650 (93% e, I°/. 8+) 5.5 ‘9 .- g; ox mmoa ocem .0000 moomommo oz» omocu CH mEEmw >ox mam on» go conmHEo no Loouo CH omCMno on» no omsmoop omcmno :me,H .mpmo pcomona map CH Hcomopa uoc mm: pcmCHEmpcoo wchpHEm COLuHmoa m0£0 .0cmcHEmucoo m CH mCOL00moq mo mocmmmga on» go omsmomn oHucm oomfi Lmoc mchoa mpmo wC0LocuH .0: oocohmumm CH oocHELouoo opoz m0C000000000 :oHpmHoLLOo ommheo .m: monopomoms .3: mocmpouoxo .mm mocoaouomo .mpmuofimhma monHE ocm moocmzoom £000 on» go mmofioco 0:0 000me00 on own: some 00; .:0000mcmpu >ox 000 on» go .02000000000 COHmpo>c00 Hmcuoch on» 00:0 .0000 co0pm0ospoo powwoso 0:0 8000 pmc0egopoc moocosoom cHom ocm woflpmg mcHxHEm e 0.0 H 00.01 . 0.0 H 00.0 00010.0 0 0.0 H 00.01 00.0 H 00.0 0001000 0 0.0 H 00.01 0.0 H 00.01 000010000 0 0.0 H 00.0 00.0 H 00.01 00001000 0 0.0 H 00.0 00.0 H 00.0 0001000 0000. H 000.0 0000.0 H 000.0 . o0.00.0 H 000.0 0000.0 H 000.0 0.000.000xa0m.00- . 0.0 H 00.01 00.0 H 000.0 00010000 1 0.0 H 00.0 00.0 H 00.01 00010000 m.HIHmOQH0Hm.mI _ to u00_0.0 H 00.0 0000.0 H 000.01 0.0w0000w0.01 0.0w00000w0.01 0\000.000\001.000\00 0.0 H 00.0 000.0 H 00.01 00010000 00.0 w0m0sw00.0 00.01w0000n0.01 m\000.0001000.000000 0.0 H 00.0 00.0 H 00.0 0001000 .0000.0 H 000.0 0000.0 H 000.0 00.00000000.0 0.010000000.01 a\010.000\000.0 0x0 0.0 H 00.0- 0.0 H 00.0 000-000 0000.0 H 0000.0 0000.0 H 000.01 00 0.0 + 000.01 0000.0 + 000.01 . - 0000.0 H 000.0 0000.0 H 000.01 00.0-w00000w00.01 00.0w0000we0.01 0\00000\000.000.00 00.0 H 000.0 000.0 H 000.01 00001000 No 00 c0mmoMWMMWMW¢ z< m< mmmwwwwm mucoHonuooo COHpmHophoo cowommo. amOHummIdetz moan coHuaHoLLoo LmHJHC< mEEmGImEEmc we. no anCE3mII.ofl oflome 0H 105 summary of the multipolarities and mixing ratios which are suggested by these results is given in Table 11. Also listed in the same table are multipolarities assigned in previous investigations. Because of the large uncertainties in the Au values, all of the interpretations of the decay scheme were based on the A2 values only. In all cases the experimental and theoretical Au coefficients agreed to within the experimental uncertainties. Although, in general, any one experimental correlation function is consistent with more than one set of spin assignments, combining the results for several cascades involving common levels has strongly suggested unique values for some of the states. The spin values assigned from this study are those in the decay scheme shown in Figure 20. A summary of the interpretation is given below. 3.2.2.D.1.-—The 1366,1213, 270 and 0 keV States.--The only two Spin sequences for the 1366, 1213, 270 and 0 keV levels which are consistent with log ft values, multipolarity assignments from conversion electron studies (38, 39, “5) and previous angular correlation measurements (39, AU, MS) are ll/2‘, 9/2+, 7/2+, 5/2+, or 9/2‘, 7/2+, 7/2+, 5/2+, respectively. 0f the cascades studied in this investigation only that involving the 153 and 9A2 keV transitions which depopulate 106 .m>Hm:HocoocH mpHSmom o .2: oocohomomo .m: monopomomn .mm oocopomomm 00.02 Lo 00 0000 0m 0m 00 0000 00200.000.0m 00.02 00.02 00 0000 00 .02 00 02 0000 02 02 02 0000 00 0000 00.02 02 0000 o 0m.02 0000 o . 000 o 02 msm 00m 000 o0 000.02 00.02 02 000 A00 000 op 000.02 00.02 00.02 000 000 000 o0100 so 00000.02 000000.02 00.02 02 000 I 0m.02 02 000 00200.000.0m 0m 0m 00 000 . . . 0>000 pcomopm o 00 pm opwsHm o 00 pm ommomnw m 00 no wuoooo>m coHpHmcmpe mpHpmaomesz oomoadgm .mLOpmepmo>cH mSOHpm> mp UocmHmm< moHuHhoHoaHasz mo COmHHmQEooII.HH manna 107 the 1366 and 1213 keV levels, respectively, yields a correlation function which is consistent with only the former spin sequence. However, the 9u2-27O keV cascade produced an experimental A2 value which required a most liberal allowance for experimental error in order to be consistent with the latter sequence, whereas this A2 value is in agreement with theoretical values obtained from the first Spin sequence. Although the results of these angular correlation measurements strongly suggest the spin sequence of 11/2‘, 9/2+, 7/2+, and 5/2+, for the 1366, 1213, 270 and 0 keV levels, reSpectively, a number of additional remarks should be made. In order to produce an A2 value which is as large as the measured value, even with a liberal error, the El 153 keV transition must have approximately a 0.1% M2 admixture. Because of this M2 admixture in the 153 keV transition, there must also be an M3 admixture of comparable magnitude in the predominately E2 1213 keV transition. While the El + M2 admixture is not too surprising, to the best of our knowledge, an E2 + M3 combination has never been observed. As can be seen in Table 10, the mixing parameter for the 9U2 keV transition changes sign in the 9H2- 270 keV as opposed to the 153-9M2 keV correlation. This is consistent with a well known triple cascade theorem (61). 108 3.2.2.D.2.--Other Levels.—-Except for the case of the four levels discussed above, at least two possibilities still remain in the spin assignments to the other states. It should be noted that,with possibly one exception, the correlation measurements are consistent with the most recent conversion electron study assignments (M5). The possible discrepancy exists for the case of the 1&0? keV state, where a 9/2' spin assignment has been made previously (U5). The negative 6270, which has already been established, does not permit the observed A2 value for the 1137-270 keV cascade unless the proposed El transition is appreciably (a few per cent) M2 admixed. Either a 7/2+, 9/2+, or 11/2+ assignment would be consistent with the correlation results. The 1013—1213 correlation leaves 9/2, 11/2, 13/2 as the possible Spin assignments for the 2226 keV level. From correlation measurements on the 912-153 and 912-(153)- 1213 keV cascades, the spin of the 2278 keV level must be 9/2‘ or 13/2‘. The 912 keV transition is from 20 to 70% E2. From the 2089-270 keV correlation, an ll/2+ assignment can be ruled out for the 2360 keV state, and ll/2- is unlikely since then the 2089 keV gamma would have to be M2 with about a 20% E3 admixture. 109 A Spin of 9/2 is the most probable value, making the 2089 keV transition almost pure El or Mlu+ E2. No reliable evidence was obtained for making spin assignments to the 10U8, 1250, 2129, and 228“ keV states. 3.2.3. Decay Scheme of 1178Te 3.2.3.A.--The Gamma Ray Singles Spectrum --Gamma ray singles spectra were recorded with several Ge(Li) detectors. Below 1800 keV, a 0.8 cm3 counter with 6 3.0 keV FWHM resolution for the 662 keV gamma of 137Cs was used. The efficiency for detection of weak high energy transitions was increased with a 7 cm3 counter whose resolution was 2 “.5 keV FWHM. Portions of typical singles spectra are shown in Figures 23 and 2D. A list of transitions and their relative intensities is given in Table 12. Halflife measurements were performed on the 720, 1091, 1278 (D.E. of 2300), 1717, and 2300 keV lines. Two series of 8 min runs were taken--the first set spanning about 80% of a halflife, the second about 1.5 halflives. Corrections were made for dead time and source decay. The mean value obtained was 1.1“ hours, with an average deviation of 0.08 hrs from the mean. The value of 1.1Mh is in agreement with values of 61:2 min,l.li0.lh, 1.1:0.1h and 65:5 min reported by reference 32,33, 34, and 35 reSpectively. 110 .quompmc A0qvmu mac 0 m 2903 vmopoomu .>mx coma zaomeonaaam 3000p 09000 mo 53000000 mm0mC0m mm .000 «00.232 .62qu0 09%. om» com 0mm 1.6.9.1....03. .....xxatr . . i3? . 00 2 0...... - , m .. I\ D 2 . é, : .. - . l j... . m m. .0... . < 73......5. rcoco. m w M m m m m mm m ..xJ. s m « - m W0 0.0/... m .00 _ m . ..w _. KJ/< . .08 oo. 0 .- .W W m/h.).r\...... .n. u w i ( m u obs: mwdwzfi m 000000. 111 IOOOO , I '0 E :3: g o N 0 = m .— 0’” I EE . IOOOd: 11 - ; A . D ‘33:;AJ . 1.11%“? {2‘2“} ....“ :1 évgfiv‘i. 8 0 I... .. .0" a D ... N O .'. . N U) 0 N E '00‘” 1:". r; a :3 “2" n o O 3;: N 3 t C) . ., a; a ”L.“ 3 o O 1 A g - J'.'°-..1l . - "' .ff , - .- IO-u. . .-.. . . n a C I i 500 750 IOOO CHANNEL NUMBER Fig. 2“ High energy portion of a singles spectrum of 117Te, recorded with a 7 cm3 Ge(Li) detector. This spectrum was recorded after approximgfiely one halflife of 117Te to allow traces of a Cl contaminant to decay out. Several spectra were recorded from sources of comparable age, and were summed to give the above spectrum. Lines at 2323, 2521 and 2617 keV are of unknown origin but decay with a halflife longer than that of 117Te. 112 Table l2.--Energies and Relative Intensities of Gamma Rays Observed in the Decay of 117gTe. Energy Uncertainty b 8'3 (keV) (keV) Relative Intensity 568.8 63u.6 719.8 830.8 886.8 923-9 930 996.7 1090.8 135u.6 1361.0 1HSN.8 1565.2 1579.9 1716.5 2213 2285 2300.0 23800 28850 |+ Nt—IOt—JI—JOr—Ioooooor—IOOOOOO H O OOOOOWOHHOOOQOKONOOOH H l\) OU'IU'IOO-EU'I our-0100142420 .IT-‘UWU'I JrU'IU'l l—' Hm 01m oommoxoxun—Imxriz-xo cow aUncertainties in relative intensity are estimated as 110% for the strong transitions. bGamma intensity only. CAssignment to 119gTe tentative. 113 3.2.3.B.--Gamma-Gamma Coincidence Results.--Coincidence experiments were limited by the l.lh halflife. Besides conventional Ge(Li)-NaI(Tl) coincidence experiments, three other types of coincidence counting were performed with the 20.3 cm x 20.3 cm NaI(Tl) split annulus. First an "any-coincidence" spectrum, employing an integral NaI(Tl) gate above the 511 keV photopeak, was recorded. A second type of experiment, complementary to the "any— coincidence," was to count only those pulses from the Ge(Li) counter which were not incoincidence with a signal from the NaI(Tl) crystal. A third type of coincidence experiment performed with the split annulus was to simultaneously gate on 511 keV photons in each half, and count the resulting coincident Ge(Li) spectrum. This established any positron fed levels and indicated double escape peaks of high energy gamma rays. This spectrum is shown in Figure 25. Other coincidence spectra were recorded with the NaI(Tl) detector scanning essentially all of the spectrum above 600 keV. To compensate for the short halflife, strong sources were used at the start of all coincidence counting, leading to an appreciable number of chance events. Hence, interpretations of the coincidence spectra must be based not necessarily on the presence of'a given line but by its relative enhancement from singles relative to other lines. 11H _ .00000mcd 0n» :0 00000000 003 83000000 000000 pc0o0oc0oo wc0 Ip0zm0p 0:» 00003 .2mmnouonc >00 00m 0:» so @0000 003 0:05:20 0:» 00,0003 5000 .00000000 000000 50 0 0 0:0 0303::0 00000 0090002 50 0.00 x 50 0.00 a a» 3 00000000 09000.co 0:05000020 00200002000 000000 0 no 0005000 mm .000 m28£5_033210 8.2 e... .0. 00.. e x 0 i m. . «w a C ” «.’....» m . . 200w /.... 0.. .50 . ...... M . ”ml ...? 0 a. yr . : .m.\wm «2:40-313 .... ». ... 02.8 00.25 . ....m of... m ... o 0000. 115 Because counting could be done for only relatively short periods at a time, most coincidence spectra exhibit regions with large statistical fluctuations. In order to ascertain whether a number of possible peaks were more than background fluctuations, most of the coincidence runs were repeated with different sources. Coincidence evidences were obtained for all lines of less than 1800 keV energy which could be observed in singles spectra. In addition, several other possible gamma rays were suggested by some coincidence experiments, but these did not reproduce well enough to warrant their - placement in the decay scheme. The results of the coincidence studies are summarized in Table 13. Several typical spectra are shown in Figure 26. 3.2.3.C.—-PositronaGamma Coincidence Results.-- Positron—gamma coincidence spectra were recorded with a 3.80m X 0.5cm plastic scintillator Tijtfi;B) and a 7.6cm X 7.6cm NaI(Tl) detector. Gating regions in the NaI(Tl) spectrum were selected at 511, 720, 92M, and 1717 keV. The resulting coincident positron spectra confirmed that there is no significant positron decay to the ground state of 1178b. Because of source thickness, window thickness, and the inherently poor resolution of plastic scintillators, reliable spectral shapes of the Fermi ll6 Table l3.--ll7Te Gamma-Gamma Coincidence Relationships. Gamma in Coincident gammas Figure NaI(Tl) gate in Ge(Li) spectrum (keV) (keV) 25 511-511a 72o, 92h, 997, 1091, 1717 26B 720 635, 997, 1091, 1565, 1580 26C 887 92“ 260 92m 887, 1361 26C 930 1355 26D 1355 930 26D 1361 92D 26D 1455 831 26E 1717 568 b >1850 none observed aTriple coincident experiment. bSpectrum not shown. COUNTS (ARBITRARY UNITS) 117 10' ~- Io' «- Io’» Io'+- |ool.O) to be placed unambiguously. The proposed decay scheme, shown in Figure 27, accommodates all of the gamma rays observed in this investigation. It should be stressed, however, that because of the short halflife, a number of the very weak high energy transitions that were obServed could not be conclusively assigned to the decay’of 117gTe. Because of the very low count rates, only upper and lower limits of about 2h and 30 min, respectively, can be placed on the halflives of these gamma rays. Of these, the 2380 and 2885 keV lines are the most likely candidates for positions in the 119%Te decay scheme- probably as ground state transitions. The other lines, in spite of the poor statistics, appeared to decay with halflives different from 1.1 hours. One contaminant which could definitely be identified was 119 1/2"' INT. g I/Z 5/2)’ 2500.0 \Jmm/ IZOO. |.5% . 5.2 |200.' 5.5% . 5.5 . 4% . 5.5 _____,-_ _____zzn 1500.0. Q¢t~QQQQd 0 fi V n -' a 2'0 :0 o b o o o a " 013: . I 9 a; N w / (1/2.5/21 * 1 '"" 1610.6 1706,1675; 6. I / o.151.3"1.5.o wag/2r 1 17125 1600. 117.5% 6. ' 0.6%3’). 5.6 I“. 0. ‘2 F. I3 6 g a at a. / 9 ° " °’ :1 2 2 1 1456.6 / 2050. 0.2% . 7.2 1 1554.6 2150 . 0.8% . 6.6 I O 0 CD I «t' v' v I) I) n | ’- " "’ l ‘1? 2 1112,5/2) 1 925.9 2600. 13.25“. I O.8%B’).6.6 I 8 9 1112.5121' 1 " 719.6 2600. (40966. i 14%8’) . 5.6 l , . 1 g b 2/2’1 } o llTSb Fig. 27 The proposed decay scheme of 117Te. Weak transitions of 2380 and 2885 keV, which could not be definitely assigned to the decay of 117Te, have been omitted. 120 3801’ small traces of which were always present after rapid chemical separations of the tellurium parents from the SbCl3 targets. Comparison with the 3401 spectrum (62) allowed several of these high energy lines to be discarded. Three levels that are heavily fed by positrons are indicated at 720, 929, and 1717 keV by the 511-511- gamma coincidence spectrum, Figure 25. The lines at 695 and 1278 keV are assigned as double escape peaks of the 1717 and 2300 keV gamma rays, respectively. That no cascades exist among the 720, 924, and 1717 keV transitions can be seen from Spectra taken in coincidence with these regions. In each case, the presence of the other two lines can be accounted for by chance coincidences and underlying Comptons in the gate. Strong coincidences between the 720 keV region and the 997, 1091, and 1565 keV gamma rays, and between the 928 keV region and the 887, 1355, and 1361 keV lines confirm the 1717 keV level and suggest additional levels at 1811 and 2285 keV. Further evidence for the level at 2285 keV is provided by a 2285 keV transition, by the suggested presence of 928-1361 and 930-1355 keV cascades and by the presenée of the 831 keV line in coincidence with the 1855 keV region. The intermediate levels of the above two cascades are placed at 1355 and 1&55 keV from relative intensity considerations. 121 The 1355 keV levels may also depopulate to the 720 keV state as is suggested by the trace of the 635 keV line in coincidence with the 720 keV region. The 1M55 keV level has not been found to involve any transitions other than‘the 831-1&55 keV cascade. Some fragmentary evidence has suggested the 1u55 keV transition to have a half life that is slightly longer than l.lhours. However, most of the discrepancy can be accounted for by poor statistics. Additional coincidence data show the 569 keV transition takes place from the 2285 keV state to the 1717 keV level. The absence of the strong 2300 keV line from the "any-coincidence" spectrum indicates a state at 2300 keV. The 2300 keV state also depopulates to the 720 keV state, as is evidenced by the trace of the weak 1580 keV line in coincidence with the 720 keV region. No coincidence experiments involving the high energy transitions are feasible at this time. Estimates from singles and coincidence counting rates indicate that at least a 24 hour counting time would be necessary with fresh sources produced at frequent intervals, to obtain conclusive coincidence data for any of the lines above 2300 keV. A very striking similarity” exists between the decay scheme of 117Te, Figure 27, and that of 1198;Te, Figure 19. A comparison of the two figures shows the 122 two schemes to be alike in energy level structure and in beta decay branching ratios. This suggests the decay of 117 Te to be that of a low Spin parent. The ground state spin of 117Te is known to be 1/2+ from atomic beam measurements (63). If this is indeed the decay of the ground state, then tentative spin and parity assignments can be made for some of the levels on the basis of log ft“ values. States at 720, 1717, 1811 and 2300 all have -u.0: log ft 55.8, indicating allowed beta decay (6H). Hence, these states should all have positive parity and J = 1/2 or 3/2. Slightly higher log ft values for the remainder of the levels indicate allowed or first forbidden beta transitions, implying J = 1/2, 3/2 for these. That these assignments for the 720 and 92“ keV states are consistent with other data and systematics in this region will be discussed in the following sections. 117m 3.2.3.B.--The Search for Te.--3.2.3.E.l.-— Systematics of Odd A Tellurium and Antimony States.-- As shown in Figure 28, excited states of J = 3/2+ and 11/2- can be seen to migrate upward in energy with r decreasing neutron number, in l2)Te, 123Te and 121Te Isomeric transitions, originating at the 11/2‘ states, are known to occur in all three isotopes (15). However, 119m while Te is known to exist, no isomeric transition l23 .meOpOmH we“ uponnwfimc on» Ca mcofipamoo pawn» Song mcoapmaoomppxm an ompmoofl mgm memfifl new mmaaa soc mamsma_um\aa . cam +m\m one .meOuOmH :mem CH mHm>mH ucfisa 204 mm .wam mmmzsz 205.an _m as Nb m» m» .5 mm hm mm LR IIIRB ..IILE uuu+~\mx/ K: II: ..N: I....+~\_ link: ulltq.) I / III I III\\\-~\__ // / \\-~\: // / \ III/ I \ -N\: / / lllx / RE xx \-~\._ / x \ / xlllll / «\m/ \ / ... // \ IN\__// / x / /.l|llu 1 x , +N\m// \ -~\: / / IL // // -3: ..III qum. IN\:// + ./ . /|I.I.I. -N\__ owhdJomdmhxw Ill 4Im CH om>pmmno mm monouOmfi 72m m CH mam>ma mcfixa 20a mm .m«& mmmzzz zomeamz V b N h Oh mm m m ..le. ...... fi/lw n ”as ...... fl ...... .3 \ +~\~// \ \ / x982 , \ / \ / \ I \\ Kt. / mefl / I / / lllll / QB aux: \\\l..~\n / / 'Iu\‘ .7 \ \fixm #va \lll/ 1+8 t \\ \ +N2 [kl lll.\ \\ ///.III I FN\mv \\\ //A+N\: III] II ./ I' \erE 5.5 / r3: \\ // \ I \ / \ / Il\ 1' r~\_v A+~\mv 3.682 23; z. mama... 30.. CON Doe 000 com 000.. (ABM) ASHBNB 126 An alternative explanation for the absence of an identifiable 117m Te activity can be sought from the case of 115Te. A 275 keV M3 transition in 115Te‘has been reported to have a halflife of approximately 0.1 sec., suggesting a 7/2.'. excited state (65,66). Hence it is possible that a 7/2+ level may exist below the ll/2- state in 117Te, making deexcitation of the ll/2- state comparatively rapid. 3.2.3.E.2.--Experimental Results.--Attempts to identify an isomeric activity 117m Te were primarily based on a search for a 530 keV gamma ray depopulating a Spin 7/2+ state of this energy as predicted from systematicS'and observed via (3He,d)reactions(5um56). First, no evidence was observed for any gamma ray activity having a halflife longer than about 2 minutes but shorter than 1 hour. Second, a thin target of antimony metal was bombarded to produce the highest available ratio of 117Te to 119Te. The chemically extracted activities were followed for several days. A very weak, but unquestionable, peak at 530 keV became evident as the 16h, 1198Te activity decayed away. Since this line was present in a spectrum recorded immediately after subsequent specific tellurium chemistry, it must be associated with the decay of some tellurium parent. 127 Third, a search was made for the 2.5h daughter of 118 119 117Te. The antimony daughters of Te and‘ Te were periodically extracted from the source, but the prominent 160 keV transition in the decay of 1173b could not be identified in the samples.” However, the amount of activity expected was extremely‘small, and could have been masked by the presence of small amounts of 119Te impurity. Fourth, assuming that any 117mTe would be produced in approximately the same ratio to 117gTeas llnge is 1198Te, a far greater amount of the 530 keV produced to gamma activity Should have been present if this transition does indeed originate from 117mTe. Also, because of the large beta disintegration energy, a far richer gamma ray spectrum can be anticipated. That most of the beta decay of 117mTe would go directly to the ground state of 117Sb (third order forbidden transtion) is very unlikely on the basis of systematics in this region. Hence, while the existence of an isomeric state 117mTe, with an appreciable halflife, cannot be definitely excluded, it is suggested to be very unlikely.“The fact that the 530 keV gamma ray is associated with a tellurium parent, or with an aetivity which survives specific tellurium chemistry, remains at present, a mystery. The ‘resolution of this problem is complicated by the very low intensity of this gamma ray relative to the gamma rays of 1lnge, which are always present as contaminant. CHAPTER IV DISCUSSION OF RESULTS Because beta and subsequent gamma decay populate only a limited set of energy levels, only a limited amount of information can be obtained from beta and gamma spectroscopy experiments. Hence it is very difficult to present a complete and fair test for nuclear models from these experiments alone. In the case of the antimony isotopes, additional information has been obtained from (3He,d) experiments. Wherever possible, these results are compared to those of our investigation. Then the two sets are combined in order to make some qualitative comparisons with theoretical calculations. “.1. Comparisons with Reaction Studies and IdentifiéatidnS”of”SomevCdrreSponding'States= AS of this writing, at least three independent sets of different eXperiments have been performed to investigate the levels of odd mass antimony isotopes via the (3He,d) reaction (SM—56). Because of a larger experimental uncertainty in the reaction energy measurements, some quantitative discrepancies with respect to results of the gamma decay data exist in the level energies. However, several states can be identified as being common to the (3He,d) results and 128 129 to the gamma ray studies. Also a number of levels exist which were populated in only one of the two types of experiments. In some cases this uniqueness can suggest possible Spin values for the level. A comparison of the various states observed in our investigation with those populated in (3He,d) experiments is Shown in Tables 1“ and 15 and Figures 30 and 31 for 1198b and 117 Sb. Table 1A and Figure 30, also include states observed by Graefee g§_al. (A5) in a recent high resolution gamma ray investigation of 1198b. It can be seen that the results of the two independent gamma ray studies are in excellent agreement. No published reaction data exist for the case of 1291. Hence, any discussion of this isotope must be confined to levels populated by beta decay. From existing data, some corresponding levels can 117Sb, 119Sb and 121Sb. These states be identified in and some of their properties are listed in Table 16. The lowest of those states which have been tentatively assigned as having Spin 1/2 and 3/2 have also been observed in the previously mentioned (3He,d) reactionr experiments. The 7/2+ and 5/2+ states have also been identified in the (3He,d) reactions and in the beta decay ll9mTe and 121mTe. However, as already discussed in of Section 2.3.E of Chapter III, the 7/2+ state could not be established conclusively as being present in the decay 130 Table l4.--Experimentally observed energy states in 119Sb. Present Graeffe Barnes Ishimatsu Bassani Investigation et al.a et a1.b et al.C et al.d (s-y decay) (s-v.d) <3He,d> <3He, d) <3He, a) 0.2703 0.2706 0.261 0.27 0.268 0.385 0.6441 0.6443 0.635 0.66 0.604 0.6996 0.7000 0.695 0.71 0.668 1.0481 1.0483 1.2126 1.2127 1.249 1.2496 1.328 1.315 1.338 1.3385 1.335 1.3658 1.3658 1.37 1.370 1.407 1.4066 1.460 1.487 1.4874 1.49 1.640 1.7491 1.7495 1.820 1.8222 1.830 1.808 1.950 2.075 2.129 2.1293 2.118 2.225 2.2260 2.215 2.278 2.2778 2.280 2.264 2.283 2.2836 2.360 2.3603 2.355 2.346 2.545 2.702 2.776 8Reference 45. bReference 56. CReference 55. dReference 54. 131 Table 15.-—Experimentally observed states in 117Sb. Present Barnesa Ishimatgu Bassani Investigation et al. et al. et a1.C (B-v decay) 1(3He,d) (3He, d) (3He, d) 0.530 0.52 0.530 0.7198 0.725 0.72 0.700 0.9239 0.941 0.92 0.915 1.337 1.32 1.328 1.355 1.389 1.38 1.455 1.47 1.570 1.681 1.7165 1.8106 1.79 1.778 1.99 1.840 2.14 2.172 (2.213 2.24 2.21 2.244 2.285 2.28 2.300 2.320 (2.380) ' 2.443 2.41 2.502 2.52 2.562 2.629 2.61 (2.885) 2.88 2.98 aReference 56. b Reference 55 . CReference 54. (KEV) ENERGY 2800 2400 2000 l600 l200 800 400 Fig. 132 - EXPERIMENTALLY OBSERVED STATES IN "'Sb I ll llllll — fl — d =-_---— ———————————————— _— — ———————————————————————— _ . ——-——_—_- ------------ _ - -———-—--——_ ___——_——————————— I! - _————————————-—_~~-§. —————————————— ~~“~ . d — — —— — ‘ PRESENT GRAEFFE BARNES ISHIMATSU BASSANI INVEST. et al. et al. et al. et al. (ayoecm (Ayoecm (3He,d) (3He,d) (3He,d) 3) Comnarison of love a in 119”. . 1 ~ is populated 67 Jean oecav to those observed in (3He,d) reactions (54-56). ”he :40 sets of 3-y levels were established independentlv and at about the saue time. Rota sets are shown for confirmation. Klara possible, corresponding levels have been suggested. (KEV) ENERGY 2800 2400 2000 IBOO I200 800 400 F1”. 133 EXPERIMENTALLY OBSERVED STATES IN "’Sb ——————_—-—_———____ - - PRESENT BARNES ISHIMATSU BASSANI INVESTIGATION etal. etal. etal. Comparison of 1178b levels ponulated by beta decay to those observed in (3He,d) reactions ( 4-56). The B-y set is less complete than that for 1 98b beca 17m of the absence of an identifiable isomeric decay Te. 134 Table 16.-- Properties of Similar states in odd mass antimony isotopes. b Tentative Energy Fractional decay to Isotopea Spin (keV) log ft 1/2+ 3/2+ 5/2+ 117 1/2+ 720 5.6 — — 119 1/2+ 644 5.5 - - 121 1/2+ 573 6.3 - 0 117 3/2+ 924 .6 — . 119 3/2+ 700 6.6 0 - 1.0 121 3/2+ 508 7.0 - - 1.0 117 l/2+.3/2+ 1717 5.6 0.21 0 0.79 119 l/2+,3/2+ 1749 6.1 0.17 0 0.83 117 l/2+.3/2+ 1811 5.8 0.70 0.30 119 1/2+.3/2+ 1820 6.4 0.63 0.37 0 121 aValues for Sb taken from Reference 9. bNormalized to 1.0 for total gamma decay of level. CDash (—) indicates decay energetically not possible. 135 117m 125Sb of a possible Sb to , as can be seen in Figure 29. In fact, if a least squares parabola is fitted to the energies of these states, relative to a state with a given Spin, as for example the 5/2+, the points typically deviate by less than 1% from the curve. A similar situation holds in the case of the odd mass iodine isotOpeS. No theoretical explanation of this phenomenon is available at present. Attempts to correlate it with the parabolic dependence of semi- empirical mass formulas have not proven very satisfactory. The two levels in the 1700 and 1800 keV region 119 117Sb and Sb. From the Similar can be compared for energies, log ft values, and decay branches to other levels it appears very likely that the 1717, 1811 and the 1749, 1820 keV pairs represent analagous states in 117Sb and 119Sb, respectively. It appears that an 1800 keV state may also have been excited in some of the (3He,d) experiments. Similar considerations can be applied to properties of several states in the odd mass iodine isotopes. These states are listed in Table 17. In this case, however, the decay properties do not allow as sharp a correspondence to be made as was possible for the antimony isotopes. It Should be noted that some of the differences in the decay branches may be attributable to differences in energetics. ”136 Table 17.--Properties of similar states in odd mass iodine isotOpes. bc a Tentative , Fractional decay to Isotope Spin Eniggy log ft 7/2+ 5/2+ 3/2+ 125 3/2+ 188 6.3d 0.02 0.98 - 127 3/2: 203 10.2 0.09 0.91 - 129 3/2+ 278 7.5 0.61 0.39 - 131 3/2 493 _7.5 0.87 0.13 - 125 5/2+ 372 . 0 1.0 0 127 5/2+ 417 7.0 0.12 0.85 0.03 129 5/2+ 488 6.1 0.15 0.82 0 025 131 5/2+ 603 6.2 0.20 0.80 0 127 11/2+9/2+7/2+ 715 8.9 1.0 0 0 129 11/2+9/2+ ' 696 9.3 1.0 0 0 131 11/2+9/2+ 774 9.0 1.0 0 0 127 9/2+7/2+ 649 10.7 1.0 0 0 129 9/2i7/2+ 730 9.8 1.0 0 0 131 ll/2+9/2+ 852 9.5 1.0 0 0 aValues for 1251, 1271 and 131 67, 10, and 11, respectively. b I taken from References 'Normalized to 1.0 for total decay from level. C-Dash (-) indicates decay energetically not possible. ~8Estimated from data given in References 15 and 67. 137 4.2 Comparison with the Core—coupling Model Some qualitative agreement with the core-coupling model can be found for the case of 1198b and 1291. Detailed comparisons with existing calculations, however, indicate large quantitative discrepancies. The comparison has not been extended to117 Sb primarily for two reasons. First, only low Spin states have been experimentally observed in beta and gamma decay studies. Second, although a few other states have been populated via (3He,d) reactions, (54-56) the ranges of Spins of these are still unknown. 4.2.1. Levels in 1198b AS Shown in Figures 19 and 20, the excited states of 1198b, or at least those populated in beta decay, occur in two reasonably well-defined bands. The band in the region of = 1.2 MeV could conveniently be interpreted as being due to a coupling between one phonon and the 5/2+ and 7/2+ single particle states.‘ The first excited 2+ state which is pictured as being due to a one phonon vibration in 118Sn, which could be considered as the even-even core for 1198b, occurs at 1230 keV. It should be noted that the 1366 keV state in 1193b has been Shown to have J1T 11/2‘, and, because of the negative parity, may arise from mechanisms other than the quadrupole phonon and the d5/2 or g7/2 single particle state coupling considered here. From its 138 presence in (3He,d) spectra, and from the absence of other known negative parity states in this region, it is tempting to consider this level to be an h11/2 single particle state. Additional support for this interpretation is provided by the strong beta decay branch to this level, which is not inconsistent with an hll/2 neutron changing to an hll/2 proton. The remainder of the states in the 1000—1500- keV region could then be interpreted as due to the 5/2+ and 7/2+ ground and lst excited states coupling with a 2+ phonon. Because the 1213 and the 1048 keV states depopulate primarily to the ground 5/2+ while the 1407 and 1249 decay to the 270 keV 7/2+ state, it is tempting to assign these pairs as the 9/2+ and 7/2+ members of the respective coupling multiplets. Four states, each of Spin 1/2 or 3/2, exist in the 1328-1487 keV range. These could conveniently supply the remaining low Spin members of these multiplets. However, the level order would be different from that calculated by Choudhury (62) for the 5/2+ Single particle case. The missing 5/2+ states are not eXpected to be populated significantly by direct beta decay, since these would require second and third order forbidden transitions from 119%Te and llnge, respectively. Assuming that the 5/2+ states, if they exist, would occur in this approximate energy range, one can 139 easily construct two multiplets whose centers of gravity come about 1100-1200 keV above the 270 keV and ground states, respectively. Comparison with the 1230 keV energy of the first 2+ state in 118Sn shows this to be in agreement with the Lawson and Uretsky center of gravity theorem (18) as interpreted by deShalit (2). Construction of tentative partial multiplets in the 2100—2400 keV region, which is approximately at twice the energy of the one phonon bands, gives further support for a phonon-particle interpretation. A particle-phonon coupling interpretation of this nature is also supported by the reaction data (54-56). Very weak excitation of states in the 1 MeV region was observed by all investigators, suggesting little Single particle character for most of these levels. Inelastic scattering experiments (56) with heavy ions have suggested a collective nature for states in this energy range in neighboring 121Sb and 123Sb. Results of DWBA calculations (54) are in agreement with observed cross sections for the 5/2+ and 7/2+ states, but are progressively too large (with increasing mass number) for the 1/2+ and 3/2+ levels. This suggests that while all four of these states may be primarily of Single particle character, the Single particle component in the wave functions for the 1/2.'. and 3/2+ levels decreases as more neutrons are added. It has 140 been pointed out (56) that the wave functions for the 5/2+ and 7/2+ levels probably contain large d5/2 and g7/2 components. The other states in the 1.5-2.5 MeV range and the low lying 1/2+ and 3/2+ levels, which have been strongly excited in (3He,d) reactions, then would have appreciable 51/2 and d3/2 components in their wave functions. Despite the good qualitative agreement which can be forced between experimental results and the core- particle coupling theory, incompleteness and inadequacies in the naive formulation of the theory are readily apparent. First, because of rapid phonon de- excitations, there Should exist very little cross-talk between multiplets built on the 5/2+ and those built on the 7/2+ states. Experimental evidence contradicts this. Not only do several states in the first band decay to both the 7/2+ and the 5/2+ levels, but also several states in the second band each de-excite to both sets of one phonon multiplets with comparable intensity. Next, the transitions of 2013 and 2089 keV bypass the one phonon multiplet. Crossover transitions of this nature are forbidden, as they would correspond to a simultaneous two phonon de-excitation. However, crossover transitions of this type have been observed in nearby even-even nuclei (15), such as 116Sn(3l), placing additional limitations on the surface vibration description of even-even nuclei. 141 Furthermore, states of spin 5/2+ in the one phonon multiplets should be populated, if not by direct beta decay, then at least by E2 transitions from 7/2+ and 9/2+ states in the second band. The levels at 644, 700, 1749, and 1810 keV were excluded from the above beta-gamma decay considerations in order to construct, in the absence of any specific calculations, the simplest sets of multiplets giving the best qualitative agreement with the core-coupling theory. It is quite possible that these four states may also be levels belonging to the coupling multiplets, in which case there would be appreciable splitting of the coupled levels. Similarly, it is also possible that several of the low spin states in the 1400 keV range arise from particle-two phonon couplings. Even if this is the case, the preceeding qualitative arguments for (and against) the core-coupling model are only Slightly affected. As already mentioned, the calculation by Choudhury (5) for a 5/2+ particle—one phonon coupling gives an energy level order which is very unlikely on the basis of known levels. A second calculation, performed by Pashkevich and Sardaryan (23), applies the strong coupling treatment to 1198b. Reasonably good agreement exists for the energies of the 270, 644, 700, and possibly the 1487 keV states. However, very large quantitative discrepancies in energy prevent any 142 one to one correspondences to be drawn between calculation and eXperiment for any of the other states. 4.2.2. Levels in 1291 129I In the case of , calculations of the energies of the status have been performed by Banerjee and Gupta (3) and more recently by O'Dwyer and Choudhury (4). The results of the latter of these and of the Kisslinger— Sorensen calculations (6) are compared with experimental results in Figure 32. Neither type of calculation yields energy levels which are in particularly good quantitative agreement with the experimental values. However, when trends of levels are considered across 2 l 71, 1291, and 1311 , the calculations leave a much more favorable impression. The results of O'Dwyer et_al. instead of Banerjee §t_al. were used because of better agreement with eXperiment. Comparisons in regard to transition rates could be made with the work of O'Dwyer g§_§l. (4) only Since numerical results from the other calculations were not available. In the few cases where correspondences between levels could be made, and relative partial halflives compared, there was notably poor agreement. Discrepancies were as large as a few orders of magnitude. 143 73:0 mmpmum 30H on» now 38:98 who; Hmma no.“ mmzam> mix awofipoeszv .magma 35.830 3.2..» IcmEHpmaxo o» cmLMQEoo can sz manhvsoco ocm nm>2Q.o 13 woumgoamo 30:» new 3V cmmcmhom ohm pmmcflmmflx an nonnasoawo mmpmpm one .mmcouOmH 6:33 mums Boo :H >0: H 20.32 magma mmpocm no comapmasoo < mm .mE zwmzwmomlmeZSmmi 4KDIODOIOIKU>BPO .2 mm. 5N. _m_ MN. NN_ mm. _M_ mN_ NN. nN_ n< IIIIIIJ \\I \ II \IIIIIIII \ \ x . / ON 0 I‘VA/I/ \ om“m \ \/// 0N n \ / ¢N\h // \ o \\ I/ \ /Il\\ \ // \\ \\ 1/ \ ¢N\h I / I 1.... .|\ ,- ..mm .IIIS \\ O \ x x \I\\ \ \ +N\_ \ \ \ I\ \ \ \ \\ 1 \ xx \\ \ c \\ x N: \\ .. l.\\|. .NB \ \ \ o x \\ \\\ I \ \ I \ xx \ I \\ xx \ I \ I \ I \ I I \ I I I ”x I I I \ I I I II I I I H I I \I I x I I \ I I I \ cm: I \ I I l\ I _ oz< ._ ._ ._ .n. ON. LN. on. 2. m4m>m.. >ommzm.oz_>4-»>on_ cm._.<.501_mmwmo 1 COM I 000. (A3)” ASBBNB 144 It should be noted that since the iodine nucleus ’consists of'Z = 50 + 3 protons, compared to Z = 50 + 1 for the case of antimony, greater difficulty can be anticipated in treating iodine in the weak coupling scheme. Furthermore, if the adjacent even-even tellurium nucleus is considered to be the core, then the much lower phonon energies (15) can be eXpected to add to the complexity in interpreting the level structure. Additional complications may be expected if one assumes that the three protons may couple according to Schemes different from a zero-spin pair plus an odd proton. 4.3. Comparison with Pairing and Quadrupole Interaction Calculations The Kisslinger—Sorensen calculation (6) for the odd mass antimony and iodine isotOpes shows some good agreement with experimental measurements with respect to relative motion of some low lying energy levels. In this calculation, the single particle energies for the g7/2, d5/2, hll/2’ d3/2, and Sl/2 states were chosen as existing at 0.26, 0.78, 2.29, 3.45, and 3.59 MeV, respectively, for mass number 115. A smooth A dependence, with two correction terms, was assigned to each of these values. The first of these correction terms is dependent upon the n-value of the Shell model state as well as upon the mass number of the 145 nucleus. ‘A second correction term is introduced as "a Special N or Z dependent shift." 5Values of the other parameters such as A,A and the quadrupole coupling constants are tabulated in Reference 6. The set of low energy levels obtained in this calculation is shown in Figures 32 and 33 for the odd mass iodine and antimony isotopes, respectively. Both sets of calculated levels Show impressive agreement with experimental data, Shown in the same figures, when one compares the motion of the states with mass number. However, numerical' discrepancies are evident. Also, the crossing of pairs of levels, such as the 7/2+ and the 5/2+ in both the antimonies and the iodines, is Slightly in error. The spin values of most of the higher excited states are not known well enough to allow similar comparisons to be drawn among these levels over several isotopes. Hence, the comparisons are limited to the low energy states only. Electromagnetic transition probabilities can be calculated as in Section 1.5.2, with the matrix elements taken between the appropriate states. Because of phonon admixtures in many of the wave functions, the E2 transition rates are expected to be enhanced. A striking example of this is the 942 keV M1 + E2 transition between the 1213 and 270 keV states in 119Sb. ENERGY (KEV) ENERGY (KEV) 146 I I r I ' A. EXPERIMENTAL A Sb 5| N . 8004- O\: . ::::~‘§:::_________.______.—’. l/Z‘ 40 --' \- O \. \' we+ OI- . 0 3:0“. 5/2" -400- \0 7/2‘ 8. KISSLINGER AND SORENSEN 800- .' \. . .-._——T:::::=-——=::-———-——" l/ZT 400- I \' 3/2“ 0- '¥:\‘ ' 0 5/2+ .\. ‘\\““o 7/2+ -4004 l l 1 I A - ”7' us l2l I23 I25 N . 66 68 70 72 74 Fig. 33 A comparison of the observed low lying energy levels in the odd mass antimony isotopes with the values calculated by Kisslinger and Sorensen (6). 147 The angular correlation studies indicate a very large E2 component, suggesting a considerable one phonon component in both of the states involved. This is not uneXpected for the 1213 keV level, but iS somewhat surprising for the 270 keV state. ‘However, the calculation does Show the 270 keV state to have an appreciable one—phonon admixture. The large phonon admixture can also be used to explain a hindrance in beta decay to certain states. This was first noted by Walters gt_§l. (68) for the l3lgTéfle>l3lI and later for other iodine case of isotopes (10, 49). The hindrance can be explained by the presence of a large phonon component in the wave functions for the daughter nuclei. In particular, the 3/2+ state in iodine isotOpeS is populated by the beta decay of a 3/2+ tellurium parent. The experimental log ft values are 10.2, 7.5, and 1 7.5 for 127 1291 d 131 I. an 1, respectively. These values are much higher than would be expected for an allowed beta transition between two single particle states. A large phonon component has been predicted for these states by the Kisslinger-Sorenson calculation. However, the same approach encounters difficulty when the second 5/2+ state is considered. CHAPTER V CONCLUSIONS Appreciable progress has been made in the effort to obtain information about systematic behavior of nuclei in the tin region. The new and powerful techniques of high resolution gamma ray Spectroscopy, including accurate energy measurements, high resolution coincidence studies, and to some extent high resolution angular correlation measurements, have made possible the construction of more complete and less ambiguous decay schemes than was possible previously with scintillation counters alone. One measure of the success of this investigation, and investigations in other laboratories, has been the identification of systematic motion in energy of several low lying states in both the odd mass antimony and the odd mass iodine isotopes. From the comparison of relative positions in the decay scheme and from comparisons of other prOperties such as log (ft) values and relative transition probabilities to other levels, it has also been possible to identify a few corresponding higher energy states in neighboring isotopes. However, in general, these correspondences are not as clearly defined because of the absence of 148 149 definite Spin assignments and because of the greater density of states at higher energies.‘ Information about Spins and mixing ratios Should become more readily available as more angular correlation studies are performed with large volume Ge(Li) detectors. It is readily apparent that, despite the wealth of accurate information which can be obtained, studies of gamma rays emitted following beta disintegration must be complemented by other types of experiments. As a Specific example, comparisons of levels above 1200 121 keV can not be extended to Sb because of the low beta decay energy. AS a second example, high Spin states 11 in 7Sb could not be observed because of the apparent absence of a high spin isomer 117mTe. Although recent (3He,d) experiments have provided some additional information in this region, more experiments such as other types of pickup or stripping, reaction- gamma, and Coulomb excitation are needed to complement beta-gamma studies. Unfortunately not all of these experiments are feasible for each nucleus. Based on gamma ray and (3He,d) studies alone, limited comparisons with the current nuclear models can be made. The agreement appears to be somewhat better with the pairing plus quadrupole interaction calculations than with the core-coupling model. This should not be unexpected. Since more empirical parameters are used 150 in the pairing plus quadrupole approach, better fits to data can be anticipated. However, the large region over which this model qualitatively fits the experimental results lends strong support for this type of inter- action to have some validity. On the other hand, the core-coupling model can not be rejected completely. 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Amsterdam: North- Holland Publishing Co., 1959. Fraunfelder, H., and Steffen, R. M. In Alpha-Beta-, and Gamma-Ray Sepctoscopy, loc. cit., Ch. XIX. Fagg, L. W.,and Hanna, S. S. Rev. Mod. Phys. 32_ APPENDICES 157 APPEN DI X A 158 APPENDIX A Beta and Gamma Decay Selection Rules Only a limited number of possible energy levels are expected to be populated in beta and subsequent gamma decay. It is the purpose of this section to give a brief summary of the selection rules that are most commonly used in studies involving the beta and gamma decay processes. I.5.l. Beta Decay The general expression for the transition probability in the beta decay process can be written as (69): 2 A - l“ = 217 |M|2 SEOfF (E) F (:z E0) dE t ave 1/2 0 Egdfle ESde where |M|ave is the matrix element between initial and final states, 0F(E) is the statistical factor describing the energy Spectrum of the electrons, F(:Z,E) is a correction factor arising from the fact that the created electron or positron must be described by a Coulomb wave function rather than a plane wave, tl/2 is the halflife, and the subscripts u and e refer to the neutrino and electron, reSpectively. 159 160 The correction factors F(:Z,E) and F(K) for 81 emission and K capture, respectively, can be numerically evaluated (69, 70). The matrix element |M|ave is dependent upon both the leptonic and nuclear wavefunctions and reflects the ease with which a beta transition may take place between the given states. It is useful to define a quantity f for 8+ emission and K capture as _ l po 2 2 f: - 711—5- 8 F(«I_-z,E) p (EC-E) dp O _ 4" 2 3 3 fk - m5 (z e m) EO Then the product of f and the halflife tl/2 can be written as A ave where A consists of various constants from statistical and Coulomb corrections. It has been found empirically that the order of forbiddenness of a transition can be characterized by the ft., or more conveniently, the log ft value. A set of rules can be summarized as follows (64): 1. For odd A, if log ft 1 4.0, then A J = 0, An = no and the transition is called super-allowed. 2. For Z < 80 if log ft i 5.8, the transition is allowed with A J = 0,1 and An = no. 161 3. If 5.8 i log ft i 10.6, the transition is allowed, or first forbidden withA J 0,1 and An = yes. 4. If 10.6 i log ft 1 15, the transition may be allowed, first-forbidden, or second-forbidden. 5. A beta transition is first forbidden unique (A J = 2, An = yes) if log f t i 7.6 and if the Fermi 1 plot has appreciable curvature corresponding to a shape factor (p2 + q2), where p and q are the electron and neutrino momenta, respectively. The function f has been defined 19 as (71): fl = [a (Bi —1) — b (EC-1)] r where a and b are (tabulated) constants, E0 is the maximum electron energy in mass units, and f has been defined above. 1.5.2., Gamma Decay When a nucleus in a state liJin1> with angular momentum J1 and parity n1 makes a transition via the electromagnetic interaction to a state lfJ conservation fflf>’ of angular momentum requires that the resulting gamma ray carry off angular momentum J such that J = IJf—Jil, lJf-JI+1|..... Jf+Ji, butJ'#'0 Hence, for a given type of transition, photons with several different J values may be permissible. However, as is shown later, only one or two of these values are observed in transitions in practice. Moreover, parity conservation 162 requires that n = winf be the parity of the radia- tion. According to the superposition principle, an arbitrary function may be expanded in terms of other functions which form a complete orthogonal set. Since nuclear states are eigenstates of J and n, it is useful to describe the electromagnetic field in terms of angular momentum eigenfunctions. The well-known solutions to the scalar wave equation (69) 2 (v + k2) U = 0 are m _ m U, (kr) - J (kr) Y, (0.¢) 2. where Jz and Y? are the spherical Bessel functions and the spherical harmonics, respectively, the latter being eigenfunctions of angular momentum. The corresponding vector wave equation for the spatial component A of the electromagnetic potential UL (where Q= 5(3) T(t)) , 2 (v +k2)_A_=O has considerably more complicated solutions. Two solutions Au’ which satisfy this equation, can be expressed in terms of the angular momentum operator £.= -i'h £_ 2 and of the A solutions to the scalar equation as 163 1181:: 2 LgAgugq (kr) J(J+1) n J(J+1) 11 These are referred to as the electric (e) and magnetic OW) modes of the vector potential. One important conclusion can be reached by inspecting the expressions for Au?. Because of the extra vector operator in the first of these, the two expressions are of opposite parity. Hence, for a given value of J, any J can be expected to have non— zero matrix elements in only one of these two modes. The orbital parity arising from the Spherical harmonies, Y? , operator which involves A“M is (-1)J. Hence, the vector potential has parity (-1)J for the magnetic mode and -(-1)J for the electric mode. The electric and magnetic fields in either mode can be obtained by ‘EIJJ = ' c at 5“,] = ilk 5“,] and M _ M IiuJ - EA AuJ The interactions between the electromagnetic field and N particles can be expressed as e i Hint -i=1 [ mic 91 ' A (71) + “i E1.E (P£)] 164 where e1, mi, pi, Di, and Si, refer to the charge, mass, momentum, magnetic moment, and Spin, respectively, of the 1th particle. In the Special case of kr< to state |f> via an electromagnetic transition can be expressed as _ 2" 2 Tif ' T 6913 l| wherejfE = 7%?- is the density of states available to the multipole waves. This leads to the expression already given in I.2, 817(J+1) k2J+l [J(2J+l)'.! 2 'n 2 |l Crude estimates of the transition probabilities, involving several approximations (4), Show that the ratio of the matrix element for magnetic to that for electric transitions ranges between 0.2 and 0.03. Hence, the ratio of the corresponding 165 transition probabilities is between 0.04 and 0.001. This means that for a given J, an electric transition would be expected to be about two orders of magnitude faster than a magnetic transition between analagous states with the proper parities. Furthermore, using the same approximation to the matrix element, the ratio of the transition probability of a given multipole of order J +1 to that of order J is approximately (kR)2 /(2J+3)2. More accurate expressions, known as the Weisskopf estimates, have been derived for single particle transitions. These, and the numerical values are presented in many texts, such as Reference 1, 69, and 71. AS previously mentioned, kR< < Read "unknown" I 3 Spectrum I U Q) a .. . I ”3 Read Identificatlon ) :3: m Channels of Peak j ) Obtains background, «:3 1-1 .14 I, ---*— ) centroid, area, and h g '3 g ) linear and quadratic '37-: H a. Call Background and ) energy for each "un- 3 o ; Centroid Subroutines ) known" peak. +4: 4.4 c: ) m 3 J] o u o ) 8‘ g 5 Apply Calibration ) ‘1‘ 3* 5 Equations ) a: : END Fig. 35 A schematic flow chart of the MIKIMAUS program. 'um1WWWu '