'. "".‘.UV"“S". '0'n‘V' " “>' “ n o. v d OF -RAY SPECTROSCOPY GAMMA EXCITED STATES EN , . Hf AND ”2w ' m 0 r . r . . .‘ . ~ . . . P w o ,c O .. D .. . . .. . u n O C . O . u . o C o . . , . ‘ . _... m. s... A . M am mWR _. .Qfli...“ - . 95m4 8.5.... .7: wmnuwo... . .1 m. ,0. .. f fND .mm. tang: . a , DR . .fimru 3. WM... .. ... . ”v..p.un..._.‘ “ .. _ V v V .. . 3 .51. “fr...” ‘14 . v‘.a l A ..vp.. 2‘ 3a can LIB RA R Y Michigan State Univcraity ”If. A to nun-Wm“. ( MICHEGAN STATE UNIVERSITY DEPARTMENT OF CHEMISTRY EAST LANSING. MICHIGAN 48823 ABSTRACT GAMMA—RAY SPECTROSCOPY OF EXCITED STATES IN 177Hf AND 182w by Brian Douglas Jeltema The deformed nuclei 17711f and 182W were investigated via y-ray spectroscopic techniques. The EC—B+ decay of 177Ta to 177Hf was investigated in y-ray singles and 7-7 coincidence spectroscopy. Thirteen energy levels in 177Hf were deduced; four levels and fourteen y rays associated with 177Ta decay were unknown from previous NaI(Tl) work. Logft values have been assigned to the decay, and multipolarities of several transitions have been assigned with use of earlier conversion electron data. The 182W level scheme was investigated primarily by in-beam y-ray spectroscopy. A total of 59 excited states were placed by use of three- parameter (y-y—t) coincidence data. Eleven rotational bands were deduced in this investigation and all were given collective or particle assign- ments. The ground state rotational band was seen at least to spin 12, and the rotational band based on a 1.4 us isomer was established to spin 15. Decay patterns of some bands are explained qualitatively in terms of configuration mixing, and 8-, y-, ground-band mixing calculations were carried out in an attempt to explain the apparent perturbations present in those three bands. /,c A L...) /’ ‘57) ‘ The in-beam study of 182W indicated that errors exist in the accepted decay scheme for 64 h lesze. Therefore a brief study of this decay was also carried out. Two-parameter y-y coincidence data were collected, and y-ray intensities in the region from 84 keV to 360 keV were measured. A level scheme consistent with the decay and in-beam y-ray data was established, and logft values were assigned. GAMMA-RAY SPECTROSCOPY OF EXCITED STATES IN 177Hf AND 132w by Brian Douglas Jeltema A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemistry 1974 ACKNOWLEDGEMENTS I wish to thank Dr. H. G. Blosser, Dr. P. Miller, and the staff of the MSU Cyclotron for making the experimental work possible, as well as Mr. R. Au and the computer staff for their aid in data accumulation and evaluation. The assistance and advice of Dr. Wm. C. McHarris and Dr. W. H. Kelly has been very helpful and is greatly appreciated. Dr. R. A. Warner and Dr. T. L. Khoo have provided many helpful discussions during my stay at MSU, and in addition have been invaluable during the experimental portions of this project. The other members of our research group deserve special thanks both for assistance and for warm friendship extended during our acquaintance. I wish to thank Dr. G. Sletten for furnishing some of the targets used in these experiments, and Ms. Lee Creswell for typing much of the manuscript. Finally, I especially wish to thank Dr. F. M. Bernthal for suggesting this field of study, and for his interest, support, and friendship of the last two years. I acknowledge the financial assistance of the National Science Foundation, the Atomic Energy Commission, and Michigan State University. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS .. .. .. .. .. LIST OF TABLES .. .. .. .. .. LIST OF FIGURES .. .. .. .. I. INTRODUCTION .. .. .. .. .. II. THE DECAY OF 177Ta TO 177Hf .. .. A. Introduction .. .. .. .. B. Experimental and Discussion .. III. THE IN BEAM y-RAY STUDY OF 182w.. .. A. Introduction .. .. .. .. B. Experimental .. .. .. .. C. Experimental Results .. .. D. Construction of the Level Scheme 1. Even Parity Bands .. .. 2. Odd Parity Bands .. .. E. Summary and Conclusions .. .. IV. THE DECAY OF 182mRe TO 182w .. .. BIBLIOGRAPHY .. .. .. .. .. iii PAGE 13 13 14 16 24 36 65 72 74 83 TABLE LIST OF TABLES Results of Coriolis-Mixing Energy Fit for Even-Parity States in 177Hf .. .. Characteristics of Detectors Used in Study of 182w y-Rays Observed Following the 180Hf(a,2n)182W Reaction at 26 MeV .. .. .. . Parameters Obtained in Three Band Mixing Calculations .. .. .. .. .. Results of 3—Band-Mixing Fits .. .. .. gK from Branching Ratios for 182W Bands .. Comparison of Experimental B(E2) Rations with Alagas Rules for the y and KTr = 6+ Bands .. y-Rays Associated with the Decay of 182”’Re iv PAGE 15 19 49 50 56 6O 76 FIGURE 10 ll 12 LIST OF FIGURES The y-ray singles spectrum of 177Ta. A Cd—Cu absorber was used to attenuate the intense x—rays and llB—keV transition .. .. .. .. .. The 177Ta decay scheme. All transitions are placed on the basis of coincidence data except those associated With the 873.0-kev level 0 o o o o o I o o o The in-beam E-ray singles spectrum resulting from the 180Hf(a,2n)1 2W reaction .. .. .. .. The high—resolution in-beam y-ray singles spectrum resulting from the 180Hf(a,2n)182W reaction .. .. The integral coincidence spectra obtained for 182W Coincidence gates associated with the K1T = 2_ octupole band I. O. O. O. O. O. O. O. Coincidence gates associated with the KTr = 2_ octupole band (Contd.) .. .. .. .. .. .. .. Coincidence gates associated with the K1T = 6+ band Coincidence gates associated with the KTr = 7- band Coincidence gates associated with the KTr = 8- band A partial level scheme for states ranging from ground to 2230.6 keV in 182W. All known transitions are shown. Dots are below those transitions placed on the basis of coincidence data obtained in this study. Asterisks (*) behind y-ray energies indicates that the transition is known only from decay studies [Ha6l, Sa70, Ga72]. The level at 1137 keV is taken from Kleinheinz et a1. [K173]. .. .. .. .. .. .. . A partial level scheme for states ranging from 1487.5 keV to 3734 keV in 182W. All known transitions are shown. See figure 11 for significance of dots and asterisks .. .. .. .. .. .. .. PAGE l7 18 25 26 27 28 29 32 33 FIGURE l3 14 15 16 17 18 19 20 21 22 23 24 25 The band structure assigned for states deduced in 182W. The symbols n and 0 indicate whether proton or neutron single particle orbitals form the dominant configuration. Dotted levels indicate that the band assignment is tentative, and energies in parentheses indicate that the level is tentative .. .. .. The even—parity bands observed in 182W. Only the two most intense transitions associated with each level are shown. Refer to figure 13 for level energies .. .. Coincidence spectra associated with the ground state band in 182w 0. O. O. O. O. O. O. Coincidence spectra associated with the ground state band in 182 W (Contd ) .. .. .. .. .. .. The excitation function for some y-rays observed in the 180Hf(a, 2n)182W reaction. Normalization of the 14 + 12 points is arbitrary .. .. .. .. .. .. A plot of 21/h2 vs. hzwz for the ground band of 182W .. + A plot of energy vs. I(I+l) for the ground and KTr = 10 bands in 182W . .. .. .. .. .. .. [E(I)—E(I—l)]/21 plotted vs. 2I2 for some rotational bands observed in 182W .. .. .. .. .. .. The diagram of Nilsson states for 182W assuming deformation parameters of 82 = 0.235 and an = 0.04. The Fermi surface is placed arbitrarily just above the orbitals known to form the ground state in neighboring odd-A nuclei. Level energies not corrected for pairing. The prompt and delayed coincidence spectra for the 518.5—keV gated transition .. .. .. .. The prompt coincidence spectra associated with the K1T = 10+ isomeric band .. .. .. .. .. The odd parity band structure observed in 182W. Only the two most intense transitions associated with each level are shown. Refer to figure 13 for level energies [E(I)-E(I—1)]/21 plotted vs. 212 for the K" = 2‘ octupole band in 82W .. .. .. .. .. .. vi PAGE 35 37 38 39 40 41 43 45 53 62 63 66 67 FIGURE 26 27 28 PAGE The high—resolution y-ray singles spectrum associated with the decay of 64 h 18sze .. .. .. .. 75 Levels of 182W populated in the decay of 64 h 182mRe .. 79 Selected coincidence gates associated with IBZmRe decay 80 vii I. INTRODUCTION The ultimate goal of nuclear science is to determine the exact wavefunction for nuclei. While this is a goal which will almost certainly never be attained, it is possible that the forces acting within a nucleus that determine its properties can be understood. In search of this knowledge, many sophisticated experimental tools are available for the study of nuclear structure and properties, one such tool being y-ray spectroscopy. In the so-called deformed regions of nuclei, nuclear properties are strongly influenced by the existence of a static nuclear deformation. The degeneracy of the magnetic substates in a given "j" shell is split, and nuclear excitations resulting from rotation of the deformed system exist. It is of interest then to characterize the nuclear collective parameters so that intrinsic and coherent excitations can be understood. The use of in—beam y-ray spectroscopy (i.e. the study of y-ray spectra produced in the deexcitation of the compound nucleus produced in a nuclear reaction) is a technique which works very nicely for these studies, as levels associated with high spins not generally populated via B-decay can be investigated. On the other hand, the study of y-ray spectra associated with B—decay can also be very useful, as the B-decay selection rules can provide information about excited nuclear states. This thesis contains the results of a study of the deformed nuclei l77Hf and 182W, an investigation carried out via the techniques of radioactive decay and in—beam y—ray spectroscopy, respectively. Some properties of the intrinsic, vibrational, and rotational states in these nuclei are discussed, and the results of calculations are presented which describe the nuclear excitations in terms of the accepted phenomenological models. Such a study is useful for defining the parameters in the models which describe nuclei, and for allowing systematics of nuclear properties to be investigated. II. THE DECAY OF 177Ta To 177H£ A. INTRODUCTION Recent years have seen intense study of the odd neutron Hf and W isotopes because of the presence near the ground state of the positive parity states associated with the strongly mixed i13/2 family of Nilsson single particle orbitals. Much of this earlier work employed in-beam y-ray spectrosc0py, using primarily (a,xny) reactions on appropriate Yb or Hf targets. The study of the rotational band structure in such nuclei can yield significant information on the wave functions associated with the intrinsic single particle configurations. Such data are of special interest because of their apparent relevance to the phenomenon of "backbending" rotational structure recently observed in several even-even rare earth nuclei. Theoretical analysis of the perturbed rotational band structure in both odd-A and even-even nuclei requires as much information as possible about the higher-lying perturbing Nilsson states and their associated rotational bands that mix into the lower—lying bands observed in the (a,xny) experiments. Such information on higher states can often be obtained from decay scheme studies. The EC—B+ decay of 177Ta to levels in 177Hf offers hope for a better understanding of at least one such case where the {13/2 single particle Nilsson orbits lie low in the quasiparticle spectrum; the high spin behavior of neighboring even—even isotopes should be directly influenced by the intrinsic configuration of these high-j neutrons. The most recent 177Ta decay scheme is that proposed by West, Mann, and Nagle [We6l] from their work using NaI(T1) scintillation detectors. It thus seemed reasonable to expect that Ge(Li) detectors might produce a considerable amount of new data on this decay. As we have recently published this work [Je74], a detailed account will not be given here. Instead, only a summary of the results will be included, and the reader is referred to [Je74] for details. B. EXPERIMENTAL AND DISCUSSION The 175Lu(a,2n)177Ta reaction was carried out on a natural lutetium foil target to produce the 56.6-hr 177Ta activity. A solvent extraction technique was used to separate the Ta activity from the foil material, and y-ray singles and y-y coincidence data were taken with Ge(Li) detectors. A typical singles spectrum is shown in figure 1. The coincidence data were employed to construct the decay scheme shown in figure 2. The measured y-ray intensities were used along with previous conversion electron data [We6l] to determine y-ray multipolarities. Where necessary, theoretical conversion coefficients [H868] were employed to deduce the beta-decay branching, and long values were calculated using the tables of Cove and Martin [G071]. The state at 1002.8 keV was tentatively assigned even parity on the basis of the conversion coefficient of the 256.9-keV y—ray, and therefore would offer some prospect for association with the i13/2 family of Nilsson orbitals. The most likely candidate for this state is the 5/2+[642] Nilsson orbital and the y-ray transitions to lower—lying states in the spectrum are consistent with this interpretation. Better conversion- Ij alsoi ' -11 BWrbS ‘13NN9HD aid SINOOO _ vibe CD ~ CD ]CD '0 6'9»; V921, WW2; 9189~ ‘zsr trees.“ (7) tvbos LIJ 2269’ ._J , C) _. o ssvsx 0 Z l'809\ "939 g 8 (7') 916, usa— CD 219» [— ava». ,,__, f N epzv’ t: ass: 61:92- 9122— 2262- O I Isvz- 599; “E5 v'eoz )lV3d wns— 12m 012%— “Hem ASSI- 62H _ gser’ SAID-5.x “4:3; I l 1: i 4 Lo F~ to u) N) (V o o 0 v0 0 g CHANNEL NUMBER The y-ray singles spectrum of 177Ta. A Cd-Cu absorber Figure 1. was used to attenuate the intense x-rays and llB—keV transition. .Hw>ma >oxuo.mnw mzu nufi3 kuofioommm wmonu unmoxm mumv woawvaoafioo mo mammn mnu so vmomam mum mcoauwmcmuu HH< .mEosom mmuww manna mna .N muawfim .x. .t 3. ”swam >ommzm wI t x h _ NC .2 mm .8 V9 20.0 v% Q0 wok 5m No.0 $88 as 8.0 ‘38 3% . , . 00 S 3.0 1.9: wok Boo ms ~_.o . 99 80.0 .nB Am 80.0 \695 as No.0 .80. us 3.0 .30. o 0. «mm: "DUO OdAco© $00.04.. cwdn OFnh rNE electron data are needed to confirm this assignment, but the log ft value associated with this state is consistent with it being 5/2+[642]; the log ft's for both the 9/2+[624] and 7/2+[633] band heads are very similar to that of the 1002.8—keV state. All three log ft values are quite high for "allowed" B-decay. This is not surprising, in view of the transition over two major oscillator shells required by the 7/2+[404] + 5/2+[642], 7/2+[633], 9/2+[624] B-decay transformations. In an attempt to determine whether the 1002.8-keV level was consis- tent with a 5/2+[642] state assignment, Coriolis calculations for mixing between the known band members from other i13/2 orbitals were carried out. The experimental input spectrum of states used in the calculation includes all members of the 9/2+[624] band known from 177Lu decay [Ha67] and the two members of the 7/2+[633] band confirmed in this study. With an appropriate selection of input parameters (cf. footnote e, Table 1), the complete Coriolis interaction matrix was constructed for each experimentally known spin state, and a best least squares fit to those energies was used as the basis for predicting the location of the 5/2+[642] state. The general method used has been summarized in [Je74]. Results of the calculations are shown in Table 1. It is seen that the energy fits (calculation I) to all known eXperimental data for even-parity states are quite good for reasonable values of hz/ZJ and B, and for the Nilsson single—particle energies defined by deformation parameters E2 = 0.25 and en = 0.05. The predicted location of the 5/2+[642] state is about 1400 keV, however, considerably higher in energy than the 1002.8—keV candidate. Results of Coriolis-Mixing Energy Fit for Even-Parity States in 1771115 Table l Ifl(K) Experimental Fit Ie Fit IIf Energy 5/2 + 5/2 (1002.8) 1401.3 1002.9 7/2 + 7/2 745.9 745.9 746.2 9/2 + 7/2 847.4 847.4 847.6 13/2 + 7/2 11013 1101 1100 9/2 + 9/2 321.3 321.3 323.9 11/2 + 9/2 426.6b 426.6 425.7 13/2 + 9/2 555.1b 555.0 552.9 15/2 + 9/2 708.4b 708.3 706.3 17/2 + 9/2 882.8b 882.7 882.9 19/2 + 9/2 1086.9b 1086.9 1086.7 21/2.+ 9/2 1301.3b 1301.3 1306.9 23/2 + 9/2 1560.9c 1561.3 1558.2 dDeviation £(AE)2=0.20 X(AE)2=58.2 aRi68 bHa67 cHu73 d£(AE2) is the sum of the squared deviations between experimental and calculated energies. eParameters adopted for this fit were: h2/21 - 15.6 keV; B I ~0.005 keV; An = 750 keV; An - 51.883 MeV; ad hoc Coriolis reduction factors N 0.99, 0,n+1 a 0.80, 0.86, 0.66, 0.84, 0.99 for 9 - 1/2 through 11/2. The quasi— particle energy for the 7/2+[633] band head was decreased by 52 keV from theory. fParameters for this fit: h2/2J I 16.0 keV; B = -0.0l keV; Table 1 (Contd.) Nn,fl+l - 0.96, 0.70, 0.58, 0.68, 0.88, 0.96. The 5/2+[642] quasiparticle energy was decreased unrealistically by 510 keV. 10 A second set of calculations (II) is also shown that assumes the 1002.8-keV state is predominantly 5/2+[642]. The fit in this case is considerably worse; it was necessary to decrease unrealistically the 5/2+[642] quasiparticle energy by 500 keV, and the Coriolis matrix elements also required unusually large attenuations in this fit. It was impossible to improve the situation by any reasonable choice of deformation parameters. These calculations do not lend strong support to the 5/2+[642] assignment for the 1002.8-keV level. It is possible to imagine seniority three states which could have the indicated even parity for this state, and one can even postulate states at this energy which could be formed by coupling octupole vibrations with the 7/2-[514] or 5/2—[512] single particle states. The possibility that this state may be odd parity also cannot be dismissed until more detailed conversion electron or trans- fer reaction data are available. The remaining levels in 17711f populated by 177Ta decay are for the most part well-characterized. Members of the rotational band based on the 7/2'[514](gnd.), 9/2+[624](321.3-keV), 5/2‘[512](508.1-keV), and 7/2+[633](745.9-keV) states are known from previous work and are confirmed in this decay investigation. The level at 805.7 keV was found by Rickey and Sheline[Ri68] to be strongly pOpulated in 176Hf(d¥,p), and to have an angular distribution consistent with its assignment as the 3/2-[512] band head. The y-ray deexcitation pattern from this state, and the log fT value from 177Ta decay to this state support the assignment. 11 The y-ray singles spectrum of 177Ta also contains weak lines which, on the basis of energy sums and differences, indicate a level at 873.0 keV While the existence of this level was not confirmed by coincidence data, a level at 878 keV was seen by Rickey and Sheline and assigned as the 5/2- member of the 3/2_[512] band. Since the log ft value and y—ray deexcitation pattern determined in our decay study are consistent with this interpretation, the 873.0-keV level is believed to be correctly placed, and is presumed to belong to the 3/2-[512] band. It is tempting to assign the state at 948.0 keV to this band as well, but Rickey and Sheline identify a level at 979 keV which they assign instead as IflK = 7/2-3/2[512]. Moreover, the energy spacing between our 948-keV level and the 5/2- band member at 873.0 keV makes it most unlikely that the 948-keV state belongs to the same band, despite the y-ray feeding into the 3/2-[512] band-head at 746 keV. (The expected strong Coriolis coupling between the 3/2-[512] and 1/2-[521] bands argues further against associating the 948-keV state with the 3/2‘[512] band.) Finally, the state at 1057.8 keV is assigned as 7/2—[503], also in agreement with the transfer reaction data. This assignment is consistent with the similar log fT values to the ground and 1057.8-keV states, since the EC—B+ decay transformations 7/2+[404] + 7/2-[514] or 7/2-[503] are both first-forbidden unhindered in the asymptotic selection rules. We conclude that probable Nilsson assignments can be made for most of the states populated in 177Ta decay. Though more precise conversion electron and perhaps transfer reaction data are needed to characterize 12 the states at 948.0 and 1002.8 keV, it is evident that such decay scheme studies provide valuable information on the ordering of the quasiparticle spectrum and thereby provide indirect information on nuclear deformations in this region. 13 111. THE IN BEAM y-RAY STUDY OF 182w A. INTRODUCTION The level structure of 182W has been investigated extensively through B—decay and transfer reaction studies, but has not been studied via in-beam y-ray spectroscopy (except for a half-life measurement of an isomeric state [No7l]). Because the (a,2n) reaction can transfer twelve or more units of angular momentum, it was thought that in-beam y-ray spectroscopy would yield significant new information on the band structure of intrinsic and collective states in 182W. The study of this nucleus is of interest for several reasons. A number of high-Q orbitals are expected to lie near the Fermi surface in 182W. These should give rise to several low-lying high-K two-quasiparticle states, some of which are expected to be isomeric, since decay to the ground state band would be K—forbidden. One such isomer earlier identified was characterized in this work. The study of 182W is also valuable because there is potential for understanding the interactions between the B- and y- vibrational bands. These bands are strongly mixed, but previous empirical band-mixing cal— culations performed by GUnther et al. [0071] suffered from a lack of experimentally known states. It was hoped that this work would establish the vibrational states to higher spins, and allow more definitive calculations to be done. And finally, a study of this sort is valuable in extending the l4 systematics of nuclear properties in this region. To gain an under- standing of recent problems in nuclear physics, such as the backbending recently seen in this region [Wa73], or the anomalous hexadecapole moments measured by Bemis et a1. [Bem73], a detailed knowledge of the systematics of intrinsic and collective nuclear preperties may be very valuable. As a by-product of this project, the analysis of the in-beam data indicated that several errors existed in the accepted decay scheme for 18sze. Therefore a short section on 18sze decay has been included at the end of this thesis. B. EXPERIMENTAL A number of experiments were conducted in the course of this study. These included y-ray singles, y-y coincidence, excitation function, angular distribution, and lifetime measurements. The excitation function and angular distribution measurements, however, were found to yield little new information because of difficulties in accurately resolving weak multiplets and because the multipolarities of many of the more intense y-rays seen in-beam are known from the decay work of Galan et a1. [Ga72] and Sapyta et al. [Sa70]. The y-ray singles data were collected with a large volume Ge(Li) detector over a range of roughly 1800 keV, and with a smaller, high-resolution Ge(Li) detector over a range of a‘600 keV. The y-y coincidence measurements were carried out using two 15 TABLE 2 Characteristics of Detectors Used in Study of 182W Size and Type a) Resolution (FWHM) Experiment (keV) Q) .1 O‘ODI— O O [x O O (I) I '0’, .206 row O‘HG 0'... I19: 1. I‘OOI "I!“ room 0'92” “OI” E 'Zttl 6'SOZI 8‘19 :1 8'0: 21 run 9'00" 1'19” S'CI ll O'OIOI V010! O'IOOI WBNNVHD 83d SlNOOO CHANNEL NUMBER -ray singles spectrum resulting from the W reaction. 32 The in-beam 180Hf(c,2n)1 Figure 3. l8 WBNNVHO 83d SINOOD I I l I r a; :> x 3 O o m o m h I I C) C) f0 f0 C'ZDI 0162 E19! 9192 9199 U) I'OKZ LlJ :32! __J 23:: (l) 02:: Elm Z "I! {73 vwwz” I102 omen. U? h, r1: I I ' . 6'“ J r"; .— 912L_ "9 nu E: run N can ‘2 ”m 4 ram ram 01» VS" “no Its 0999 tom :1" — 21:. wow row 150 rue O'CCC SAN-X l'l.‘ B'Idt M. 029: Test I'ISS 1 “"*_--_ ' I “—‘*——~—~—. I 1 1 D 0 Q . O 9 9 9 ° 9 CHANNEL NUMBER 2n)182W reaction. The high-resolution in-beam y-ray singles spectrum 18°Hf(a resulting from the Figure 4. 19 TABLE 13 y-Rays Observed Following the 180Hf(a,2n)182W Reaction at 26 MeV. EY (keV)a b Assignment Multipolarityc 84.7 38 (3) 1373.8 + 1289.2 M1 + E2 100.1 350 (30) 100.1 + 0 E2 107.0 (2) 11.9 (0. ) 1660.4 + 1553.2 M1 + E2 108.4 (2) 40 (3) 1769.0 + 1660.4 Ml 111.1 (3) 4 (2) 1621.3 + 1510.2 113.5 106 (9) 1487.5‘+ 1373.8 M1 + E2 116.4 (2) 5.4 (0.4) 1373.8 + 1257.4 130.8 31 (3) 1960.3 + 1829.5 M1 + E2 133.8 41 (3) 1621.3 +1487.5 Ml + (E2) 145.4 (2) 23 (5) 1769.0 + 1623.5 E1 147.8 25 (5) 1769.0‘+ 1621.3 148.9 (2) 7 (4) 1978.4 + 1829.5 150.2 11 (2) (1660.4 + 1510.2) 152.4 100 (10) 1373.8 + 1221.4 E1 154.1 11 (2) 2114.4-+ 1960.3 156.4 87 (7) 1487.5 + 1331.1 E1 160.2 12 (1) 2120.5 + 1960.3 169.2 40 (3) 1829.5 + 1660.4 M1 172.9 30 (3) 1660.4 + 1487.5 Ml 178.5 35 (3) 1621.3 + 1442.8 E1 179.4 19.2 (1.5) 1553.2 + 1373.8 M1 + E2 Table 3 (Contd.) 20 186.7 189.6 191.4 198.4 203.6 206.1 207.7 209.9 213.6 214.4 215.4 217.5 221.2 222.0 226.2 229.3 236.1 241.7 247.5 251.3 256.6 260.2 262.3 (2) (2) (2) (2) (2) 5.6 12 29 53 16.2 4.6 13.2 5.0 17.0 54 33 20.3 15.0 64 61 1000 21.2 '25.7 79 58 56 12.0 46 (0.8) (1) (2) (4) (1.3) (0.7) (1.1) (0.5) (3.0) (4) (3) (1.6) (1.5) (6) (6) (2.1) (2.1) (6) (5) (4) (1.0) (4) (1810.9 1810.9 1960.3 1487.5 1960.3 1829.5 2328.0 (1978.4 2328.0 1971.1 1769.0 1660.4 1978.4 1553.2 2204.5 329.4 2564.1 2212.8 1621.3 2455.8 1809.7 2824.3 2492.9 1623.5) 1621.3 1769.0 1289.2 1756.8 1623.5 2120.5 1769.0) 2114.4 1756.8 1553.2 1442.8 1756.8 1331.1 1978.4 100.1 2328.0 1971.1 1373.8 2204.5 1553.2 2564.1 2230.6 Ml E2 E2 (M1) M1 E2 E1 E1 E1 M1 E2 E2 M1 Table 3 (Contd.) 21 264.0 267.4 275.3 276.4 279.8 281.5 283.0 286.6 290.4 295.9 298.8 299.8 302 313.6 318.7 320.2 323.4 339.1 341.6 345.4 351.1 355.9 357.0 (2) (3) (2) (2) (1) (3) (2) (2) (2) 25.6 8.3 13.4 19.0 11.7 51 16.0 22.0 15.0 25.0 12.0 19.0 13 56 11.0 55 27.8 17.2 22.4 800 32 56 (2.0) (0.9) (1.3) (2.0) (2.3) (4) (2.0) (3.0) (3.0) (2.0) (3.0) (2.0) (5) (1) (5) (2.0) (5) (2.2) (1.4) (2.3) (60) (6) (8) 1553.2 2480.2 2731.1 1829.5 3104.1 + + + .). + 1769.0-+ 2775.9-+ 1660.4 + 2770.6-+ 3029.9-+ 1960.3-+ 3077.l-+ 1756.8 2087.7 3397.3 + + + 1810.9-+ l960.3-+ 1829.5 2114.4 680.5 2334.3 2274.0 + + ..). 1289.2 2212.8 2455.8 1553.2 2824.3 1487.5 2492.9 1373.8 2480.2 1621.3 2731.1 1660.4 2775.9 1442.8 1769.0 3077.1 1487.5 1621.3 1487.5 1769.0 329.4 1978.4 1917.0 E2 E2 E2 E2 E2 E2 E2 E2 Table 3 (Contd.) 22 362.4 372.5 399.8 406.8 414.6 437.2 452.3 464.0 514.1 518.5 534.5 558.2 567.6 586.2 660.6 740.1 927.6 943.3 1001.8 1076.4 1086.5 1113.5 1121.4 (3) (2) (3) (3) (2) (2) (4) .a- 13.0 27.4 56 13.2 26.6 27.6 21.2 480 12 63 9.7 8.5 222 21.3 49 6.5 17.7 8.9 35 60 73 56 245 (1.5) (2.2) (5) (5.0) (2.1) (2.2) (1.7) (40) (3) (5) (0.9) (1.7) (18) (1.7) (4) (0.7) (1.8) (1.8) (3) (5) (6) (5) (20) 2131.4 1993.8 2487.5 2323.8 2225.5 2711.2 2446.1 1144.5 2739.6 2230.6 2980.6 2770.6 1712.1 3077.1 2372.7 3112.8 1257.4 (1623.5 + + .+ + + ..). 1769.0 1621.3 2087.7 1917.0 1810.9 2274.0 1993.8 680.5 2225.5 1712.1 2446.1 2212.8 1144.5 2492.9 1712.1 2372.7 329.4 680.5) 1331.1 + 329.5 1756.8-+ 680.5 2230.6 + 1144.5 1442.8 + 329.4 1221.4 + 100.1 E2 E2 E2 Table 3 (Contd.) 23 1157.7 1180.5 1189.1 1221.8 1230.9 1257.2 1293.9 1342.3 1410.9 1426.8 1454.3 (2) (2) (2) (2) (2) (5) (5) (3) 23.3 32 103 166 139 34 51 52 51 17.5 (1.9) (3) (8) (13) (ll) (3) (4) (4) (1.6) (5) (1.9) 1257.4 1510.2 1289.2 1221.4 1331.1 1257.4 1623.5 1442.8 1510.2 1756.8 (1553.2 _) + 100.1 329.4 100.1 100.1 329.4 100.1 100.1 329.4 100.1) E0 + (M1) + E2 E1 + M2 + E3 E2 E2 E2 aError is 0.1 keV unless otherwise indicated. bNormalized to the 229.3-keV y-ray. cTaken from Ga72. Errors in parentheses. 24 are shown in figure 5. Weak contaminant y-rays resulting from the tantalumwwire and the 180Hf(04,3n)181Wreactionwere present, but were easily identified from previous studies of these reactions [Li73, H368]. No contaminants from the 180Hf(a,n)183W reaction were identified. Because of the wealth of coincidence spectra generated from this experi- ment, only some of the more important gates are shown here, and these can be found in figures 6 through 10. The lifetime measurements revealed only one isomeric state, located at 2230.6 keV, which decays into the ground band via transitions of 518.5 and 1086.5 keV. This isomer had already been observed by Nordhagen et al. [N071] to have a half-life of 1.4 us, and will be discussed in more detail in the section on positive-parity bands. The timing experi- ments make it possible to place an upper limit of 5 us on the half-life of the other 182W levels populated in-beam. D. CONSTRUCTION OF THE LEVEL SCHEME The level scheme for 182W was deduced primarily from the coincidence data, and is shown in figures 11 and 12. Much of the level structure below 2 MeV was known from decay work [Ga72, 8870], although several errors exist in these decay schemes. A difficulty encountered in the analysis was the existence of several very low energy transitions. The conversion electrons associated with these transitions were measured by Harmatz et al. [Ha61] and Ageev et al. [Ag70], and are placed in the level scheme on the basis of energy sums and differences, although some coincidence gates cannot be explained without them. In addition, some 25 1 r0» nun C"... 9299 522:: I men A H rm rm. . | s g rum E '— O 0'... L) noon F" LU L) p_ UJ UJ F- C3 LU C3 0 .é - x .. ¢-0 [\ not L3 (.3 '37. Z . z B 0 on H 9. n O I U D an _] rue _] tun E Mn) _ é run 01:: (.9 0‘9» (9 r“. UJ L1J LP— 1F}— 3‘“ Z Z H on“ 1“] 92.3.0“). 3 z N N [2 lg ('08: 1'00. WBNNVHD 83d SanOO CHANNEL NUMBER Figure 5. The integral coincidence spectra obtained for 132W. COUNTS PER CHANNEL 26 52.4 2H7.5-KEV GATE 295.8 I89e6 IIZI.4 247.4 372.5-KEV GATE 452.3 372.5 LI52.3-KEV GATE : I It: .[I J: i" I .e’" 1' * I II IIIIIIIIIII" II I ‘II IIIIIIIIIIIIIl III I I II CHANNEL NUMBER Figure 6. Coincidence gates associated with the K1! - 2- octupole band. I IMIIIIIHIIII III I. ., III IIIIIIIIIIIIIIIII II IIII IIIIIIIII IIIII IIIIIINIIIIIIII IIIIIIIIIIIIIIIIIIII II III III IIIIII IIII IIIII I I - II II I IIIIII I IIIII , 27 |56.4 ‘II 3.5 323.2-KEV GATE ISOA 492 IldIIIILIIIIIIIIIII II II III I III COUNTS PER CHANNEL ”3.5 “4.4 |.9.5 Figure 7. I333 INIIIIIII IIIIIIIIIII II II IIIIIIII IIIIIIIII'IIIIIII I II IIII III II IIIIIIII III” IIIIII iIIIIII IIIIIIII III IIIIIIIIIIIII IIIIIII III III II III CHANNEL NUMBER 247.5 189.6-KEV GATE 4+2 6 O p ‘ 0 4l4.6 0: «mum ou >ox n.5mea scum waawouu mouaum you «Boson Ho>oH Hmauuon < .NH ouowum gun. 33 7mm”- ----III-I-I--I--I-II-III--IIII-I-I-II-I---- -IIIIIII: ---IIIIIII:-IIIIIIIIII-----IIIIIIIIIIII-- .----I----III-- -I--.-I--I--w..n_w----8.~.+w: 34 y-rays too weak to be seen in-beam are known to exist from 18sze decay. For completeness, all transitions known to exist from the y-decay of excited states in 182W are shown on the level scheme, but only the y-rays actually seen in-beam are listed in table 3. The y-rays which are placed on the basis of the in—beam y-y coincidence data are indicated by dots underneath the arrows, and levels which were placed on the basis of weak coincidence evidence or energy sums and differences were dotted to indicate that the level assignment is tentative. All levels known from 182”’Re decay are also populated in-beam with the possible exception of the 1960.7-keV state. As will be discussed in the section on 18sze decay, this state is difficult to detect by coincidence techniques because of the intensity of y-rays from the 1960.3—keV state. Experimental conditions in-beam.make this state even more difficult to detect, so that it was impossible to determine through the coincidence measurements whether the state was being populated. Spins and parities assigned in the level scheme are based on the assignments of [Ga72] and [K173]. When band structure could be extended beyond that seen in these references, spins were assigned based purely on the expected regular spin dependence of the band members, and are indicated as tentative on the level scheme. A useful way to decompose the level scheme is to separate the states into rotational bands, and this has been done in figure 13. A large number of bands are populated in—beam, probably due to the large number of low-lying high-K states in the nucleus. The bands are constructed on the basis of y-ray decay patterns, not shown in figure 13 due to the 35 ROTATIONAL BANDS IN 'Bzw flihnfl «mum ELM: «mm: mm on.“ w 0.sz Ill qnxu1 gala“ “2U“! lien: Nil”! mm um mm um 9:12; mm: H m. " “ u “I, um w an" ELI”: w K-IO «as ,l I". H624] £524] {ii-:1: m m M "-1 “I? ”(6'51 ‘ 1’ new . 3593] :5'41 K=6 rim sum m1 2.1m o = , . m 541,2] “624: {[624] £432] 44“ LJm- sum “5'2 itsno] w , m V V {I404} K34 m m 7" “5241 Luna “.1“ use] m I . “4“ 1:42“ m OCTLPOLEn—Jm ' K30 Y-BAM) M 8M0 4.9—!” 3-3m) gun .91....9 K-O GROUND 8AM) Figure 13. The band structure assigned for states deduced in 182W. The symbols w and v indicate whether proton or neutron single particle orbitals form the dominant configuration. Dotted levels indicate that the band assignment is tentative, and energies in parentheses indicate that the level is tentative. 36 complexity of the decay. 1. Even Parity Bands There were five even parity bands observed in this study. From figure 13, these are seen to be the ground, 8, and Y collective bands, a K1r = 6+ two-quasi-proton band, and the K1r = lO+ isomeric two—quasi- neutron band. A partial level scheme of these bands including the prominent y—ray transitions is given in figure 14. The B- and y-band assignments are taken from Kleinheinz et a1. [K173]. Through the y-y coincidence experiment we were able to establish the ground state rotational band definitely up to I = 12, and tentatively up to I - 14. The coincidence gates for this band are shown in figures 15 and 16. The 14 +'12 transition at 740 keV is seen as a very weak line in the 12‘+ 10 gate, and is even less apparent in the other gates. However, a y-ray of this energy is definitely seen in singles, and the excitation function shown in figure 17 is in agreement with the 14 + 12 assignment for this state. At 24 and 26 MeV, the 740-keV y-ray could not be seen, but at the higher beam energies, the line became apparent. Since this y-ray was not seen in 181W’[Li73], the assignment as a transition from a high spin state seems justified. A plot of ZJ/h2 vs. hzwz for the ground band is shown in figure 18. The point associated with the tentative 14+ state deviates slightly from the line defined by the other members of the band. This nucleus presents a particularly interesting case for the study of backbending because of the identification of the K1' = 10+ two—quasi- 37 - w--snn- . Woe-74 w.¢1 flceuzlfilll¢lofiu l! . . . m L I . wen" i l,“ : Noocn n '3 . . v. m "m «.03 weenie—$63 m n u" . . . m .n. v .u u n 1 I. . ".o r; . 'o o .o. - II ‘9 n . _5 2 n a 2 1|I|II_.oI. moon 0...: 0...: +“ + + + M" m m a 6 air.» Otdmun+t ti..th h._¢N K —*-(p—qbo p--- -------—----- r «a «$3. I3 n..u V5.2. i n K 22! i ” ado: . . a v. w n . K=O The even-parity bands observed in 182W. Only the two most intense Figure 14. Refer to figure transitions associated with each level are shown. 13 for level energies. COUNTS PER CHANNEL 38 3 , 2-0 GATE 1 4 | “i 9 In: " 3‘ I. 1‘" § L i L+~2 GATE I. o «'a z 3 B-H GATE J o T +- I‘ a -I .5 I : 3'," ‘3 EE .. I ‘f «E 9.22 3 Figure 15. CHANNEL NUMBER Coincidence spectra associated with the ground state band. COUNTS PER CHANNEL 39 402 6o4 8-6 GATE 2-00 I0 48 '5 i O + z 9 3' 'f 33 § 3? I 3 . ; 12-10 GATE 2 Z :3 l I E g T _ ‘ I I ' _ , ”WWW!“iIllIIJIIIIMlIIIII.Ii.III.I.I.II HIIH IIIIIWI. ”I :I. CHANNEL NUMBER ‘ Figure 16. Coincidence spectra associated with the ground state band. 40 .%Hmuuanum ma mucHon NH + «a map mo cowumufiamauoz .COMuommu 3NmHA2N.svmmomH wSu cw wo>pwmno mmmuIr meow How cowuucsm cowumuwoxw one .NH muswwm fi w\\\\\\\\m|A: \\\\\\\\\\\ >9. 0.0.0 \ \o \ Tim. NeII¢_ i\ $2): >0mm2m 24mm on oi mm WW I «N .llllumov « l. .III\II¢IoII\II\I\..I1 . 3:. toe :2 Scan. cozozoxm EAIlV'lHH AllSNElNI 41 (.-AaINI .BNmH mo pawn wasouw mzu now mama .m> Nc\HN mo uoaa < .wH musmfim 1%.; N35 m_. S. N_. 0._. m0. mo. 60. N.O. 00m U¢Z 0m 3? 42 particle band. As will be discussed later, the intrinsic structure of this band is based on a triplet coupling of the Q = 9/2 and Q = 11/2 ilg/z neutrons, and in the Stephens and Simon model, it is the i13/2 neutrons nearest the Fermi surface which would be involved in backbending in 182W [St72]. Figure 19 shows a plot of E vs. I(I+l) for the ground and K = 10 bands, and it is apparent that the two bands should cross at about spin 16. At this point one might expect the two bands to become sufficiently mixed for prominent interband transitions to occur. In addition, backbending could occur in the ground band if the particles forming the K = 10 band were to become sufficiently decoupled from the nuclear core. However, if the Stephens and Simon model holds, it is possible to predict that backbending should in fact not occur in 182W. This prediction rests on calculations of Bernthal [Be74a] in which the degree of decoupling is determined for the adjacent nucleus 181W. The calculations show that in 181W the i13/2 neutrons that could produce backbending behavior remain strongly coupled to the deformed nuclear core, even at relatively high spins. By implication, backbending should not occur in 182W. The fact that the K = 10 state in 182W is a 1.4 usec isomer, and the band structure associated with the isomer remains relatively unperturbed to spin 15 at least, indicates this expectation is borne out. It would be most interesting to examine the behavior at the spin-l6 band-crossing point, for one could then hope to extract matrix elements for mixing of the g.r.b. and the K = 10 band if inter- band y-ray transitions were indeed observed. However this possibility 43 ' I v I r Energy vs I(I+l) for the lsomeric 4000’ and Ground Bonds of '“W . P 'I ISOMERIC BAND . C 3000’ .. ENERGYP # (keV) ./ ZOOOr GROUND BAND I000 \ o l J— 0 50 I00 I50 200 250 I(I+') 1". 30 .--p------------------------------------------- ------------- I Figure 19. A plot of energy vs. I(I+l) for the ground and KTr - 10+ bands in 182w. 44 cannot be explored until a reaction can be done which transfers more angular momentum into the product nucleus. Such a reaction would be the 182Hf(a,4n)182W reaction, which would populate higher spin states in 182W because of the higher incident beam energy. This reaction requires a target of 18211f, which is unstable with a half—life of 9 X 106 y, and which can only be produced in quantity by double neutron capture on 18on. An alternative method of populating high-spin states in 132W is by the 176Yb(9Be,3n)182W reaction. However, the difficulties inherent in working with beryllium make such beams rare, so that this experiment was not feasible at this time. The ITr = 0+ member of the 8 band was not seen in this work, and is taken from Kleinheinz [K173]. The vibrational states decay via E2 transitions directly to the ground band [Sa70, Ga72]. These strong interband transitions are primarily a result of the energy dependence of E2 transition probabilities, rather than mixing with the ground band. This conclusion is based on the fact that the IN = 3+ and 5+ members of the y-band cannot be mixed with the ground band, but display decay properties similar to those of the y-band states of even spin. A plot of [E(I)-E(I-l)]/21 vs. 212 (i.e. a "trumpet" plot) for the y-band is shown in figure 20, and it is clear that the band is highly perturbed. In an attempt to account for the observed branching ratios and energy spacings, three-band-mixing calculations have been done by GUnther et a1. [GU72] using unperturbed ground—, B~, and y—band states as a basis set. However, these calculations did not include the 4+ member of the 8 band or the 5+ member of the 7 band. Therefore, we 45 .SNmH Ga co>ummno momma Hmcowumuou maom HOW NHN .m> vmuuoam HN\HAHIvaIAHVmH .om ounwfim b P .8 Com CON On. 00. On 4 _ . . _ .omv own cm» 0%». : Imuhx o\\. / I 1 o/e/ . +O_uh.Y_ 0’0 N; 0 IV nerv— o T0 I O \O O/ 1 Imuhx Imuhv. o/. I INuLMx/J/o/ o I 1.0/0 +mlh¥ /0/ 1 1 >3.. 5 CO rmvccm 6:02.33”. .2 LN m.) :ICMHWSVM amen»A I + Ih o o p — p O. N. v. w. m. IZ (I'IIEI- (DB 46 have also done similar band mixing calculations in hopes of reproducing the energies of these states. The diagonal matrix elements are given by [GU72] EKG) = EK + A.K[I(I+1) - K(K+l)] + 131([12(I+1)2 — K2 (K+1)2] (1) while the off-diagonal elements are given by _ AK=2 (I,yIHcoupII,GSB> — /2(I-l)I(I+l) (1+2) (ylh |GSB> ( = AK=0 I.GSBchouplI,B> I(I+1) I -—- 1.75 i- 0.06 keV (4) as well as the unperturbed energies of the B and y ITr = 2+ states, i.e. ES. = 1252.7 keV (5) EX. - 1226.1 keV As a check on these calculations, note that the 3+ and 5+ members of the 7 band remain unmixed within the framework of this calculation, so that the energies of these states may be used to determine the y-band 48 rotational parameter and the y-bandhead energy. For BY = 0, one obtains BE. = 1233.6 keV (6) and inclusion of any reasonable B term does not significantly affect this value because of the small value of I. It is clear that these two methods of determining the unperturbed y-bandhead energy yield signi- AK=2ly>| obtained ficantly different results, so that the value of I<8|h by Gflnther et a1. may be incorrect. As a result, we have treated this quantity as an adjustable parameter in our calculations. A list of all the parameters used in the calculations is given in Table 4, and the corresponding fits obtained using these parameters is given in Table 5. Fit I was obtained using the parameters given by Gfinther, and it is clear that the calculation fails to account for the energies of the highest experimentally observed 8 and y states. In Fit II, the moment of inertia parameters of all three bands were constrained to have the same value, while in Fit III this parameter was forced to be identical only for the ground and y bands. The fits were obtained using the computer code BETABLE [St68], which adjusts the input parameters such that the best least squares fit to the experimental energy spectrum is obtained. Accordingly, it is doubtful that a better fit to the data could be obtained without including additional adjustable parameters. Fit IV was obtained by matrix diagonalization using a rather arbitrary choice of input parameters, including a "B" term of 5 eV, and is included 49 .>Hm> ou vosoaam ones mumumamumm 02 Av .%Mm> ou vasoHHm uoa +Mm use mme .m .osam> mama msu o>mn ou voawmnumaoo muouuamumn Hmaowumuou r and mmu hano Au + .hum> ou vmsoaam uoa one: +Mm one mwwm .m mam mfinu GH .onaa> mama msu m>mn ou vocawuumaoo muoumamuma Hmaoauouom An .qa moamummou aoum aoxmu ufiw mfinu pom muouoamumm Am m~.H oo.H oo.m o.m-H meH o.o mI.mI.mI w.oH w.oH w.oH u>H NH.H oo.H om.HI N.oNNH mmaa o.o 0.9.0 m¢.oa 55.5H m¢.oH HHH mm.H mm.H MN.MI o.o-H NMHH o.o o.o.o mn.oa mm.oa mm.oH nHH mn.H No.0I mm.MI H.oNNH meH 9.0 o.o.mI om.na oa.aH w~.oa mH A: «.02: _ av a $32.19 ouuaiov +mm +mm mmwu 93m X f. 33 3m e mqm ou uosoaam was 0 < swoonu cm>m vamp m onu How confimuno on no: fiasco uwm voow m HHH may :a modem .vouommxm on vanoa mane .uam onu o>oumfia hauamoamaswfim no: 0wv hnm> ou muoumamumm Hm:0fiumuou mounu «Hm waH3OHH< Au .maOHumH>ov mam mo monam> ousaomnm emu mo Sam I _m<_w An .unxmm I admom u mafiuma>m0 Am «.am coma 0.m «.0 m.HI m.« «.ml «.MHI 0.H m.0 0.0 «.0 0.0 >H 0.Hm mwma «.mI H.MI «.0I m.« «.0 0.0HI 0.0 «.«I ¢.MI «.HI 0.0 fioHHH n.«q omna H.m H.m 0.0I H.«I «.0I «.QHI 0.0 0.mI «.0I 0.0 0.0 HH «.«0 omna 0.«« «.0 0.0 0.0 m.a¢ «.0 0.H 0.0I «.0 0.0 0.0 H A>oxv wouoavoum +n +0 +m +« +0 +« +0 +0 +v +« +0 or 930 653 990 6:3 990 E 3_m<_w +0 > you Amaowuww>on u now Amaofiumw>mn mmo How Amaowuma>mn 3E waafiauuammum mo 9:33 m m4m<fi 51 to show that a definitive set of parameters cannot be determined on the basis of these calculations. In fact, it is clear from table 5 that, while a wide range of parameters give comparable fits to the data, no set of parameters gives a good fit. Specifically, the 2+ member of the 8 band is much too low (or the 4+ too high) in all of the calculations. Thus it would seem that the positive parity collec- tive bands are not properly described by this model. There are a number of reasons why this might be the case. For instance, it may be that interactions other than those given by equations 2 exist between these states. In fact, it is well known that low-lying 0+ states in this region tend not to be good vibrators, with ground and excited 0+ states often strongly mixed [Be7l]. Thus a thorough calculation would probably require more complex interactions. It is also possible that the failure of three-band-mixing to describe the collective states is due to an additional band, perhaps K = 1 in character, mixing with these states. This possibility is strengthened by the failure of the octupole band branching ratios to determine correctly the K - 2 amplitudes in the B and y bands. As an example of how such mixing could occur, RPA calculations done by Hamamoto (quoted in IKl73]) indicate that roughly 25% of the y band is made up of the IK = 2, 3/2-[512]+, 1/2—[510]+> state. This component can be Coriolis coupled directly with the [K = 1, 3/2‘[512]I, 1/2’[510]+> and [K = 1, 1/2‘[521]+, 1/2'[5101+> state, both of which have been tentatively assigned by Kleinheinz at approxi- mately 2 MeV of excitation in 182W [K173]. In order to discuss the two-quasiparticle states in terms of the 52 Nilsson model, it is necessary to know in some detail the nuclear shape. It is especially important to know the value of the hexadecapole deformation 6n [N155], since this parameter has a strong influence on the level ordering [Be74b]. There has recently been some dispute con— cerning the value of this parameter in 182W. The hexadecapole transi- tion moment for 182W has been deduced by Bemis et al. from a Coulomb excitation measurement with alpha particles [Bem73], and their results indicate a value for an of 0.18 i 0.06, a factor of three greater than the value predicted by Nilsson et a1. [N169]. This value is also sub- stantially larger than that obtained by Hendrie (£4 as0.08) from nuclear inelastic scattering on 182W [He73]. In an attempt to determine which value of an is most consistent with nuclear spectroscopic data, Coriolis band fitting calculations similar to those done for 177Hf were carried out for 181W [Be74b]. The results indicate that the best fit is obtained for values of an consistent with the predictions of Nilsson et al. [N169]. Therefore, the interpretation of the 182W level structure relies upon the Nilsson states corresponding to deformations of 82 = 0.24 and as = 0.04 (see figure 21). This value of e” is slightly below Nilsson's prediction of £4 = 0.065, but the difference is not enough to affect the qualitative arguments to be presented in the discussion of the two-quasiparticle states . The K1T = 6+ two-quasi-protOn band is rather unusual. The 6+ assign- ment for the bandhead is taken from Galan et a1. [Ga72], and the 214— keV transition from the l971-keV state was found by Galan to be M1, in agreement with the assigned band structure. The intrinsic structure 35L 2- II- 3 O 3 35 0'- a: uJ 2! u: II— 2.— 3F- Figure 21. 53 62:.235 I/fleeo] 312*[esIJ\-——— 3/2:E402g——¥—-— II: 400 .0 II/z‘Laos]/_—,———— 3121831] I/z‘LaoI] 5/2*[402] x _________ 9121qu 7/2‘1404] I/2*[4II] 7/2‘[5233 312*[4IIJ\ BIZ-[532.] 5/2’I4l33 PRO T ON 8 3’ 2’I6 42] -— I/Z‘IBBI] ‘~ 9121505] II/ZTIe I5] , “Hz-[503] \ 3/2‘Isl 2] ‘ I/2'[5 Io] 912*[32 4] 71216 I 4] 5/2‘16 I2] _____/ / ”2'16le \ 7121033] 5121642] 1..— 5/216 2 3] 3121080 ____\ ‘ '12 [coo] NEUTRONS The diagram of Nilsson states for 182W assuming deformation parameters of £2 = 0.235 and as = 0.04. The Fermi surface is placed arbitrarily just above the orbitals known to form the ground state in neighboring odd-A nuclei. Level energies not corrected for pairing. 54 of the band is believed to be based on the singlet coupling of the 5/2+[402] and 7/2+[404] protons. The structure assignment is based on the observation that this band is seen in other even-even nuclei in this region [Kh73], and from the diagram of Nilsson states shown in figure 21, it can be seen that there is no other easy way to form a low-lying KTI = 6+ state. In addition, knowledge of the cascade-to— crossover ratios for y-ray transitions within the band makes it possible to calculate, within the framework of the Nilsson model, the amplitudes of two-quasi-proton and two—quasi-neutron character present in the intrinsic particle structure of the band. EXplicitly, the following equations may be developed [A164]: 1 + 1/52 = [(I+l)(I-1+K)(I-l-K)/21K2(ZI-l)] - {E(I + I-2)/E(I + 1-1)}5 (7) where A = Iy(I + I-2)/Iy(I + I-l) (8) and [ng - 8RI/QoI = [0.2mm ~> I-1>}2/(12-1)I - (1/62) (9) where 6 is the EZ/Ml multipole mixing ratio for cascade transitions within the band, Q0 is the nuclear quadrupole moment, and gR and gK are respectively the rotational and intrinsic gyromagnetic ratios. 55 If one assumes that gR for all rotational bands in 182W is the same, then a value for gR can be taken from measurements of the g factor associated with the ground state rotational band [G167]. The quantity Q0 can be calculated from the B(E2) values obtained from Coulomb excitation studies through the relation [SG65] Qo = [léB(EZ)/5]1/2 (10) which holds explicitly only for the ground band, but which should apply reasonably well for the other rotational bands as well. Thus gK can be deduced experimentally from the observed branching ratios. This value can then be compared with the theoretical value of gK obtained from the Nilsson model. Specifically, in the asymptotic limit [Kh73], gK -- (1/K)[gs + aim—1)] (11) gx‘gz where g8 and gz are the intrinsic and orbital g factors of the particle. Thus by comparison of the deduced and theoretical gK values, it is often possible to make a statement about the neutron or proton char- acter of the state. In the case of the K1r = 6+ band, the branching ratio for the spin 10 state at 2770.6 keV was determined and the results are given in table 6. The theoretical value of gK for a singlet two—quasi-proton state is l, which agrees with the average experimental 56 .mmqu> omoSu wdHuooumv How hocmHonwm m>HumHou mam :H huonuumoca 0cm muoommo :OHumHouuoo AMHnwsam Eoum muHomou zuchuuooan meMH some on“ wnH>Homou oH suchuuouco aoum manmou uouuo omumH .mumw moaovHoaHoo >oxI0.H¢« ecu Scum :mxmu mon> mth Au .>ox awn um amassoe .mmeaHm Eoum comma OHUmH waHsoamun mHna An .«0H0_aoum doxmu mH mm Mom mon> any .moUm scum :mHMu mH oo you oon> osH Am maouusoz m«.0I 0 mH.0Hm«.0I 0.«0m HH+MH . . I . 0«0 0+H00 0 AvH 0+ « 0 . 0H+MH mGOuoum m« H H AoMH 0+nm 0 0 00m «H+MH maouunmz «n.0I 0 0«.0Hmm.0I q.0m« 0+0H I «0.0H«H.0 Aom.0wwq.0 . 0+0H maououm 0m.H H 0«.0+«0.H « 0mm 0+0H maouusmz 0m.0I 0 mH.0H0¢.0I 0.00N 0+0H . . I, . m0 0+HH 0 Ann 0+«m 0 . 0+0H maououm mm H H 0H 0+0m 0 « wnn 0+0H umHeHue uonaHm Mm Mm AMOE—mwlmw— AszH\A«mvH hwumam aoHuHmomHH MeH AHHmoHuouomna madam ZNmH How moHumm maHsoamum Eoum M0 0 Hindu. 57 .oomom menu aH cOMHoo: w you umnu N00 mH noan mnHm> m waHm: hp hHHHmuanum umnemaom woaHmuno .oon> wonoaonu voHHmo om mnu wH GOHuMHaono mHnu QH 00m: mm mo mnHm> onH .HH maoHumsvm .00 Am .6~.on n aw 6% nouns .AszH\A~m0H 6H gonna NOOH you A6 .umHnnov 00>Homouan no mo uaoaomaoo uoHHmam onu on ou 0m>oHHon mH mmuI> >oxI0.mm ago no Aoumw >mx m.«0«v Mumv moamvHucHoo Scum vmaHmuno on hHao 0Haoo msHm> mHnH AU A.6uaoov mmeozaoom I 6 mom| (12) where the 'are the appropriate Clebsch-Gordan coefficients. It is seen that the y-band transitions systematically populate the higher-spin member of the ground band more strongly than predicted by theory. The theoretical value quoted for the K = 6 band is calculated assuming that the entire transition strength is a result of K = 2 admixture, and again the theoretical value is less than the exper- imental value, as is the case for decays from the 7 band. Therefore the assignment of the 1756.8—keV band as being predominantly K" = 6+ is believed to be correct, and the short half-life of the K1r = 6+ state is due to mixing with the 6+ member of the 7 band. The remaining positive parity band seen in this study is that 60 TABLE 7 Comparison of Experimental B(E2) Ratios with Alaga Rules for the y and KTr = 6+ Bands Transitions Experimentala) Alaga b) (IK+I'K') B(E2) Ratio Rules 7.; Deflatim‘ (22+20)/(22+00) 2.0 20.2 1.43 +40% (32+40)/ (32+20) 0.55:0. 6 0.400 +402 (42+40)/(42+20) 4.6 10.5 2.95 +60% (52+60)/(52+40) 0.62:0.3 0.571 + 9% (66+60)/(66+40) 4.8 i-O.5 3.71“) +297. a) Note that the ratio is such that the B(E2) value correspond- ing to decay to the higher spin member is the numerator. b) Deviation is defined here as (experimental-Alaga rules)/(Alaga rules). c) The theoretical value was obtained by assuming that all the transition strength is due to K = 2 admixture in the K = 6 band. For K = l, Alaga rules predict the ratio to be 0.037. 61 based on the isomeric state at 2230 keV. Nordhagen et a1. [N071] found this state to have a half-life of 1.4 us and assigned that state + + or 10 . From the diagram of Nilsson states a spin and parity of IN = 9 (figure 21), it can be seen that a low-lying KTr = lO+ state could be formed by a triplet coupling of the 9/2-[514] and 11/2-[505] protons or the 9/2+[624] and ll/2+[615] neutrons. 0n the other hand, low- + 1, + lying 9 states are difficult to construct, so that the K = 10 assignment is preferred. Since either protons or neutrons may couple to form this state, it was desirable to identify the band members based on the two-quasiparticle state so that the branching ratios could be used to determine the intrinsic character of the state by evaluation of gK. Because this state is isomeric, the Y rays associated with the intraband transitions could not be seen in prompt coincidence with the isomeric or ground band transitions. However, by setting a gate off the prompt TAC peak, delayed coincidences could be seen. The prompt and delayed coincidence spectra for the 518.5-keV gate are shown in figure 22. The 262- and 283-keV y rays are present in the delayed spectrum, and prompt coincidence gates set on these y rays (figure 23) allow the K1' = lO+ band members to be identified with reasonable confidence up to I = 14, and tentatively up to I = 15. From the 262-keV coincidence gate, the branching ratio from the 3077.1- keV state was determined for the band. The theoretical value of gK for triplet protons is 1.25, and for triplet neutrons is -0.23 (cf. equations 11), and from table 6 (cf. footnote e) it is seen that, even if the intensity of the 586-keV transition were in error by 100%, the COUNTS PER CHANNEL 62 518.5-KEV PROMPT GATE I 0' «+4 G—DG IO". L - 3 N 518.5-KEV DELAVED “GATE +- 262.3 4+2 2 03.0 II 0 ‘ II. InI‘JALI ‘IlIIl III i|lbIlikl II‘ III‘I J! ‘ 0 I000 2000 CHANNEL NUMBER Figure 22. The prompt and delayed coincidence spectra for the 518.5-keV gated transition. COUNTS PER CHANNEL 63 262.3-KEV GATE # IIHNIIIIIIIIIIIIIIIIIIIIIIIIIIfl-IIIIHIIIIIIII 283.0-KEV GATE N O n L u": .- .mm“ “I‘| I III III I II" I‘IHIIII I III III H IIIII IIIII II Ii; I IIIII IIIIhIIIII I In.“ IIII 302-KEV GATE L 3 320.2-KEV GATE "onu- "530 CHANNEL NUMBER Figure 23. The prompt coincidence spectra associated with the K1' = 10 isomeric band. I 5“; “MI ”II“! III. I? I II I :I III *. IIIIII II I I. I I IIIII IIII II l:l I II I” I . “I“ I IIII'IIIIIIIIIIII I III: IIIIII I IIIIIIIII III IIIIIIIIIIII IIIIIII Ii’IIIlII iIIII J 64 branching ratio would still indicate that this high—K band was a two- quasi-neutron band. Thus we assign this band as based on the I9/2+[624+],11/2+[615+]> state. The measured half—life of 1.4 us for the K = 10 isomer is actually much less than one might have expected. To see this, we calculate the retardation factor FW’ defined by Fw = T%(expt)/T%(SP) (13) where T%(SP) is the half-life calculated from the Moszkowski single particle estimate, given for E2 transitions by [M055] 1%(59) = £n2/[1.6 x 108A”/3E$] (14) In the case of the 1.4 us isomer, one obtains Fw = 5.2 x 105 (15) and since the transitions are eight orders K—forbidden it follows that the decays are hindered by a factor of 5.2 per degree of K-forbiddenness. However, it is generally found experimentally that decays are hindered by a factor of 10 to 100 per degree of K—forbiddenness in deformed nuclei. Thus, if the K = 10 state had been hindered by 108, its half-life would have been *‘300 us. The relatively small retardation 65 factor for the K.= 10 bandhead implies that K is a poor quantum number for the band. This would be expected from the plot of [E(I)-E(I-l)]/2I vs. 2I2 for the band (figure 20), where it is seen that the band- member spacings are somewhat compressed relative to the nearly pure proton bands. 2. Odd Parity Bands The K1r = 2- band was seen up to spin 4 in the transfer reaction work of Kleinheinz et al. [K173], and much evidence has accumulated indicating that the band is based on an octupole vibration [0072, K173, He72]. In B-decay studies, the band was established to I = 6 [Sa70], and in-beam it is excited to I = 11 (see figure 24). The higher band assignments are based on the energy spacings of the levels and the observed increase of cascade-to-crossover y-ray intensity as angular momentum increases, a result of the E5 dependence of the E2 tran- sition probability. As indicated by the trumpet plot of figure 25, the octupole band is strongly perturbed; the points form two branches with the odd spin members depressed. These odd-even shifts arise from second order Coriolis mixing with the K = 0 octupole band through the K = l octu— pole band [Kh73b]. Only odd—spin members of the K = 0 band are expected to lie at low energy, so that only the odd—spin members of the K = 2 band are expected to be significantly mixed. As the locations of the K = 0 and K = l octupole bands are not known, an experimental estimate of the interaction matrix elements cannot be made, although 66 4... 411—4 L323o4+4l 4.6+5 I 4.l 688 Figure 24. The odd parity band structure observed in 182W. Only the two most intense transitions associated with each level are shown. Refer to figure 13 for level energies. 67 .3NmH Ca mpcmn wHonduoo IN H ex mnu How NHN .m> wouuoaa HN\HAHIHVMIAHVMH .mN wusmwm «E On. 00_ Om O I I d 1 d q .2 .N. .m. .S .m. p n p b P b p IZ (I‘I)3‘(I)3 .Illl, ‘7! 68 theoretical matrix elements and bandhead energies have been calculated by Neergfird and Vogel [Ne70]. Several papers exist in the literature dealing with the properties of the octupole band [He72, Gu72], and the calculations done in these works were carried out under the assump— tion that no K - O or K = l admixture is present in the K = 2 band. The large perturbations shown by the [E(I)—E(I-l)]/ZI vs. 212 plot place this assumption in question for the high-spin members of the hand. For the low spin states, however, the assumption is probably reasonable. Note that the upper branch of the octupole band trumpet plot shows a marked deviation from smooth behavior for the point representing the energy difference between the I = 6 and I = 5 states. This anomalous ll U! point is the result of mixing with the KTr = 4- band. Because the I ll 0‘ and I = 6 states of the K = 4 band both lie between the I - 5 and I states of the octupole band, the octupole states tend to be pushed apart. In contrast, the two K = 4 states tend to be pushed together, as can be seen on the trumpet plot for this band (figure 20). The strong mixing of the K 8 4 band with the octupole band is also implied by the fact that the K = 4 states decay primarily to the octupole states rather than via intraband cascades. The K1T = 4-, 5-, and 6_ bands were all seen in the (d,t) and (T,a) reaction work of Kleinheinz et a1. [K173], and the Nilsson assignments shown in figure 13 are taken from that work. The highest state in the K a 5 band and the highest two states in the K = 6 band were seen only in this work and are assigned to these bands solely on the basis of 1" III I IliI'IlIxIlu ' I *l i’ 69 energy spacings and decay patterns. The transfer reaction studies indicated that these three bands were strongly mixed, and the inter- band transition strength seen here supports this. The remaining two negative parity bands are given tentative Nilsson and spin assignments on the basis of somewhat meager evi- dence. The bandhead at 1978 keV (figure 13) is known to be ITr = 6— or 7- from the decay studies [Sa70, Ga72], but the intense 18-keV decay to the 7- state at 1960 keV (figure 24) implies that these two states may be highly mixed, lending support to the KTr = 7- assign- ment. As the l9/2-[514+], 5/2+[402+]> two—quasi-proton state is expected to lie quite low in the spectrum, this assignment is preferred, although other reasonably low-lying neutron and proton IN = 7- two- quasiparticle states can be formed. It seems probable, however, that the band is based on a two-quasi-proton state, since the 1978-keV state decays via a strong 221-keV y ray to the K1r - 6+ two-quasi-proton bandhead. Since these bands are of different parity, no mixing can occur between them. As a result, if the K1' = 7- band were a two- quasi—neutron band, decay to the K“ = 6+ bandhead should be quite hindered compared to decays to the two-quasi-neutron states. Thus, the presence of the relatively strong 221-keV transition implies that the K11 = 7- band is a proton band. If the conclusions of the preceeding discussion are correct, then the mixing between the 1978- and 1960-keV states is an example of neutron-proton mixing. It should be noted that if this is true, the 7O mixing results from the near degeneracy of the two states. This is an important point to keep in mind, as the two states do not satisfy the conditions usually required for significant configuration mixing [Ma74]. It has generally been observed experimentally that AK = 0 for two bands which are mixed through the neutron-proton residual interaction. Of course K is not strictly a good quantum number, so that the configuration mixing might be taking place through states which are Coriolis mixed with the K = 6 or 7 bands. However, these neutron-proton mixings would violate the experimentally observed tendency of significant configuration mixing occuring only when the unpaired particles occupy orbitals on both sides of the Fermi sur- face. That this should be necessary can be seen by looking at the form of the off diagonal matrix element m for the interaction [Ma74], i.e. 'le ) (l6) m=(1p pxpz nlnzl N—P where Iwnlnz) is the two-quasi-neutron excited state, and V is the residual interaction. In the second quantization formalism, VN-P can be written as N-P : o - ‘1' '1' V = Z (uplvnphl p ) anapan' 3p, (17) npnp" where a and a+ are the nucleon annihilation and creation operators. For the case of parallel couplings of the proton and neutron angular 71 momentum, the off diagonal matrix element becomes [Ma74] IMI = |(u v u v + v v < —' " > n1 n: P1 P2 mun: Plum) n1 PZIVnplnzpl (18) - u v v u + v u u v < .— ' ._ > (n1 n2 Pl P2 n1 n2 P1 p2)n1p1IVnpln2p2 I where u and v are the usual occupation numbers defined in the BCS treatment of the pairing interaction [Be159]. The important point to notice is that in the pairing factors of equation 18, only the combination uv occurs. Because u is large for orbitals above and v for orbitals below the Fermi surface, the product, and thus the off-diagonal matrix element, is largest when the orbitals of interest straddle the Fermi surface. In the case of the 1978- and 1960-keV states, it can be seen from the Nilsson diagram of figure 21 that neutron-proton mixing between low-lying components of the same K would violate this condition. However, the nearly degenerate energies of these two states could cause appreciable mixing even for a small interaction, so that this interpretation is still reasonable. The remaining band seen in this work is the very tentative KTr = 8 band. An interesting characteristic of this band is the sudden appear- ance of a strong interband transition out of the 2328-keV state. This branching can be understood if the 2120.2-keV state were I1‘ = 8- and it were mixed with the ITT = 8- state of the K1' = 6— band at 2114.1 keV. Since the perturbed energies are only 6 keV apart, an interaction matrix element of only 3 keV (in the approximation of two—band mixing) 72 would account for the splitting if the states were initially degen- erate, and Coriolis interactions could easily account for a matrix element of this magnitude. The perturbations implied by the trumpet plots for these bands are also consistent with mixing between these states. And finally, from the Nilsson states shown in figure 21, one would expect the K1r = 8- band to lie slightly below the KTr = 10+ iso- meric band, as this band does. On the basis of these arguments, the band is tentatively assigned to be a two-quasi-neutron band formed by the triplet coupling of the 9/2+[624] and 7/2-[503] neutrons. E. SUMMARY AND CONCLUSIONS As a result of the presence of a large number of low-lying high- K bands in 182W, the in-beam investigation produced considerable new information for high-lying members of an unusually large number of rotational bands. The apparent success of the Nilsson model in pre- dicting the observed two-quasiparticle states for the deformation para- meters 62 = 0.24 and s4 = 0.04-0.06 indicates that the spectroscopic information supports the nuclear deformation predicted by Nilsson, and argues strongly that the deformed shell model gives at least qualita- tively an accurate description of nuclear structure in this region of the periodic table. Because of the current interest in backbending and the exPer- imental identification of the K = 10 two-quasi-neutron band, it would be of interest to examine higher spin states in 182W. If the K = 10 band were to become sufficiently decoupled at higher spins, backbending 73 behavior could appear in the yrast band and would be proof that the i13/2 neutron band crossing model of Stephens and Simon is qualita- tively correct, at least in some cases. Thus the 176Yb(9Be,3n)182W reaction would be a very interesting reaction to study. It would also be of interest to determine whether the K = 10 isomer occurs in 181‘03, an isotone of 182W. This nucleus apparently does display backbending +1 in the ground band [Wa73], and it is conceivable that the "KTr = 10 I band is responsible for the behavior, though a band structured from a more conventional Stephens-Simon type recoupling of the two i13/2 neutrons nearest the Fermi surface may also be present near the "K = 10" band in 18“Os. In conclusion, it is clear that many more data for high spin states will be needed before the collective and intrinsic structure of such states can be completely understood. The relatively large number of collective and high-K two-quasiparticle bands observed for 182W should be a valuable aid in achieving this understanding. 74 IV. THE DECAY OF 132mRe TO 182w The decay of lasze was investigated principally because the in- beam y-ray spectroscopy study indicated that errors existed in the current decay sCheme [Sa70, Ga72]. The principal tool used in this study was the two-parameter y-Y coincidence technique. In addition, the high-resolution singles spectrum shown in figure 26 was collected so that y-ray energies and intensities in the complex low-energy region of the spectrum could be measured accurately. The 18sze activity was produced by bombarding a 1 -mil natural tantalum foil with a 4l-MeV beam of alpha particles produced by the MSU cyclotron. The source was allowed to cool for four days to elimr inate 13 h 1828Re. Coincidence data were taken at 90° geometry with detectors of 18% and 10% efficiency. Table 8 lists the y-rays placed in the 182mRe decay scheme, which is shown in figure 27. Some coincidence gates associated with this decay are shown in figure 28. Figure 28a shows the 226.2-keV gate, and it is seen that the 221.6-keV y-ray is the most prominent line in the spectrum, indicating that the 226.2-keV y-ray is a transition to the 1978.4-keV level. The presence in this spectrum of y-rays associated with the 1960.3-keV level requires the existence of the intense l8-keV transition seen by [Ha61] from the 1978.4-keV level. Figures 28b and 28c show the spectra associated with gates set on the high- and low-energy portions of the BOO-keV doublet. It is apparent that the gates are very similar, and 'w I I T T j C C) O 3" 10'!!! 001‘! or": u'ooc ‘orou on 'u a 3 o In” fl "‘ 8 ll '0" ! m “'9" IV": 3 m 3* 55’ 2 Iron 0 - % Z ‘0'!" 'n‘iu " .'. _ ”'40! m U) m t 2 OI'OOI < arm 3 D 2 U _ o «J LIJ onu\ o L” Q in“ N % ATOM 2 < was I .. 2 .. gr "3:." 3 won or“: : 00"" % 0mm 1 48 or» 9. SAVU-X { g _ .-l_ L l 1 (0 n :r m N G: O 0 e s wafihvsa 83d Sifihoa y-ray singles spectrum associated with the decay of h-resolution sze. 5 The hi Figure 26. 64h1 y-Rays Associated with the Decay of 18sze 76 TABLE 8 Energya) y-ray b) Energya) Y-ray b) Intensity Intensity 18.05 - 160.1 9.3 (0.6) 19.85 — 169.15 440 (30) 31.7 34 (16) 172.87 139 (9) 39.1 12 (3) 178.47 88 (5) 42.7 11 (1) 179.40 117 (7) 60.65 4 (2) 187.34 12.5 (1.2) 65.8 106 (10) 188.54 5.1 (0.5) 67.85 880 (60) 189.65 15 (7) 84.68 107 (7) 191.39 260 (20) 100.11 580 (40) 198.34 157 (13) 107.13 55 (4) 203.55 19 (2) 108.58 31 (2) 206.00 20 (2) 110.38 4 (4) 208.26 24 (2) 111.07 8.1 (0.6) 209.40 19 (2) 113.68 189 (12) 214.32 43 (3) 116.23 20 (2) 215.73 30 (2) 130.81 290 (20) 217.55 127 (8) 133.80 93 (6) 221.61 250 (20) 145.43 26 (2) 222.07 330 (30) Table 8 (Contd.) 77 147.69 148.86 149.45 150.25 151.15 152.43 156.39 286.56 295.9 299.90 300.36 313.98 323.40 339.06 342.03 345.46 351.07 357.0 891.92 927.95 943.2 959.74 1001.68 (0.2) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.1) (0.3) 35 68 35 20 17 330 280 274 49 66 31 68 216 41 19 400 21 1.3 14.4 8.8 7.8 95.7 (3) (5) (3) (2) (2) (20) (20) (18) (3) (10) (15) (2) (5) (l4) (3) (2) (30) (2) (0.2) (1.5) (1.4) (1.5) (3.4) 226.19 229.3 247.46 256.45 264.07 276.31 281.45 1257.47 1273.75 1279.8 1289.16 1291.8 1294.0 1330.9 1342.72 1373.80 1387.40 1410.10 1427.29 1439.3 1453.05 1521.3 1560.4 (0.3) (0.4) (0.3) (0.2) (0.15) (0.3) (0.4) (0.4) 119 10003) 196 370 139 340 221 41.4 36.7 29.4 62.7 14.6 100 11.5 10.3 10.8 381 (8) (13) (30) (9) (20) (15) (1.2) (1.7) (0.3) (0.6) (0.9) (1.2) (1.3) (25) (0.4) (1.0) (0.7) (7) (0.4) (0.3) (0.4) (0.3) 78 Table 8 (Contd.) 1044.43 11.1 (0.4) 1631.4 (0.5) 0.49 (0.09) 1076.21 (0.15) 410 (12) 1088.5 (0.3) 7.7 (0.8) 1113.29 183 (4) 1121.28 855 (25) 1157.31 ) 48.7 (1.2) 1158.08 J 1180.8 (0.3) 21.5 (1.0) 1189.04 351 (10) 1221.42 677 (14) 1230.97 579 (11) a) b) Unless otherwise indicated, error may be taken as £0.05 keV. Normalized to the 229.3-keV y-ray. Only y-ray energies and intensities in the region from 84 keV to 360 keV were measured in this study. Energies and intensities below 84 keV are taken from Ha61, and those above 360 keV are taken from Ga72. 79 >0mw2w .0352 s so no hmoov 2.3 6H commasmon 3N3 mo 3254 KN ounwam 3... L :8. a“. Gd. .8 n4. 0.: ‘2 55 33533: 35392 333 3533 3 80 CHANNEL NUMBER “I ’1 *7 0) 226.2-KEV GATE COUNTS PER CHANNEL um o-og N8 0 me 2 3 “—— 80.0 w .m.‘ 3 II 11'! Figure 28. 1 Mill 0" "w 3' “Ilwhhb htluHHuHIIMHHIII ; b) 300.'-H