ENGINEERING RESEARCH INSTITUTE THE UNIVERSITY OF MICHIGAN ANN ARBOR TECHNICAL REPORT TO JANUARY 1, 1957 INVESTIGATION OF NUCLEAR -ENERGY LEVELS., -S J. M. ORKK Professor of'Physics Project 2375 OFFICE OF NAVAL RESEARCH, U. S. NAVY DEPARTMENT CONTRACT NO. Nonr 1224(13) SPONSORING AGENCY PROJECT NO. NR024-015

(*M2I5,-o JAR ""-l kAlR S I

FOREWORD This group of reprints of papers published in The Physical Review and the Bulletin of the American Physical Society during the year is submitted as a technical report for the year 1956. The study of nuclear-energy levels is being continued both in the Physics Department of the University and at the Argonne National Laboratory, under their Participating University Program. J. M. Cork

TABLE OF CONTENITS Paper No. DECAY OF RADIOACTIVE Ce143 (5334 hr). Phys. Rev., 101, 182 (1956). Martin, Brice, Cork, and Burson. I RADIATIONS FROM THE ACTIVE ISOTOPES OF YTTERBIUM. Phys. Rev., 101, 1042 (1956). Cork, Brice, Martin, Schmid, and Helmer. II 49 49 DECAY OF Ca AND Sc. Phys. Rev., 102, 457 (1956). Martin, Cork, and Burson. III RADIOACTIVE DECAY OF TERBIUM-161. Bull. Amer. Phys. Soc., Series II, 1, 297 (1956). Cork, Brice, Schmid, and Helmer. IV DECAY OF Mo101 (14.6 man). Bull. Amer. Phys. Soc., Series II, 1, 329 (1956). Martin, Burson, and Cork. V 161 NUCLEAR LEVELS IN Dy61 Phys. Rev., 104, 481 (1956). Cork, Brice, Schmid, and Helmer. VI DECAY SCHEME OF Pt199. Phys. Rev., 104, 1670 (1956). LeBlanc, Cork, and Burson. VII iii

I DECAY OF RADIOACTIVE Ce143 (33.4 hr)

Reprinted from THE PHYSICAL REVIEW, Vol. 101, No. 1, 182-188, January 1, 1956 Printed in U. S. A. Decay of Radioactive Ce143 (33.4 hr)* D. W. MARTIN, M. K. BRICE,I J. M. CORK,t AND S. B. BURSON Argonne National Laboratory, Lemont, Illinois (Received September 19, 1955) The beta and gamma radiations of Cem4' have been studied with a ten-channel scintillation coincidence spectrometer, with a double-focusing magnetic spectrometer, and with photographic magnetic spectrographs. Five beta-ray components and ten gamma rays are identified with the activity, and the decay scheme is established involving six excited states of the daughter Pr43 nucleus. It is found that no beta rays of measurable intensity proceed directly to the Pr'4m ground state. Spin and parity assignments are made for several of the levels. I. INTRODUCTION geometry. As shown in the insert, a lead collimator 4 HE 33-hr beta emitter in cerium was first observed inches long is used, having a tapered aperture that by Pool and Kurbatov.1 Their assignment of the defines a cone limited to the central part of the crystal. activity to Ce'm has been confirmed.2 Several investiga- A 1-cm thick slab of Lucite in front of the crystal serves tions — of the conversion- and secondary-electron to absorb all beta rays and conversion electrons. The spectra have been in essential agreement on the exist- whole assembly is enclosed in a 2-inch thick lead shield. ence of gamma rays with energies of about 0.057, 0.29, The superimposed Cs'37 spectrum illustrates the spec0.35, 0.66, and 0.72 Mev. Coincident gamma rays of trum of a single gamma ray in this geometry. 0.126 and -0.16 Mev, for which the 0.29-Mev transi- The decay of the spectrum was observed in this tion was presumed to be the crossover, were suggested5 geometry over a period of 12 days. All of the peaks were from an early scintillation measurement. Beta-ray com- found to decay with the 33-hr period except for the ponents of 1.38, 1.09, and 0.71 Mev, with possible others initially small peak at 0.145 Mev and part of the x-ray of lower energy, have been reported.4'5 Each of these peak. These can be attributed to the well-known6 single investigators has proposed an essentially different level gamma ray of Ce'4' (33.1-day). scheme. In particular, two of them have assumed that Evident in the figure are "photopeaks" for five of the the highest energy beta ray proceeds to the ground previously reported gamma rays, as well as several state of Pr'4. additional peaks. The peak at 0.493 Mev is seen, by The gamma-ray spectrum has been studied with the comparison with the superimposed Cs'37 spectrum, to be ten-channel scintillation coincidence spectrometer at the much too sharp to be due to the Compton distributions Argonne Laboratory, using cubical crystals of NaI(T1) of higher energy gamma rays. This and the peaks about 24 in. on a side and Dumont 6292 photomulti- labeled 0.232 and 0.861 Mev are confirmed to be gamma pliers. The internal-conversion electron spectrum has rays by observation of their conversion lines. The last been observed with photographic magnetic spectro- peak, at 1.10 Mev is not at the right energy for any graphs both at Argonne and at the University of expected "sum peak" (very unlikely in this geometry), Michigan. The beta-ray spectrum has been analyzed and therefore represents another gamma ray. One addiwith the double-focusing magnetic spectrometer at the tional weak gamma ray at 0.565 Mev will be shown to University of Michigan. In addition, the beta-ray exist in the discussion of coincidence spectra. No evispectra in coincidence with various gamma rays have dence is found for gamma rays of 0.126 or 0.16 Mev. been observed with the scintillation spectrometer, using The gamma rays are listed in Table I together with an anthracene crystal and an RCA 5819 photomultiplier. their associated conversion-electron lines where obSources were prepared by neutron irradiation of served. The energy values quoted are based on the cerium oxide enriched in mass 142 in the Argonne conversion data in most cases. In no case is this value in reactor, CP-5. A number of different irradiations conflict with the scintillation data. The scintillation ranging up to 37 hours were performed. spectrometer is calibrated, for the two gamma rays not IL GAMMA-RAY SPECTRUM observed in conversion spectra, with the gamma rays of Cs'37 and Co60. No definite evidence is found in the Figure 1 shows the NaI(T1) pulse-height distribution conversion spectra for any transition not observed by obtained with a freshly irradiated source in "good" scintillation. scintillation. * Portions of this research were aided by the joint support of the A photometric measurement from the spectrograph Office of Naval Research and the U. S. Atomic Energy Commission. plates of the K/L ratio proved to be feasible only for the t University of Michigan, Ann Arbor, Michigan. 0.294-Mev transition, for which the value 6.1-4-0.6 is 1 M. L. Pool and J. D. Kurbatov, Phys. Rev. 63, 463 (1943). 2 M. L. Pool and N. L. Krisberg, Phys. Rev. 73, 1035 (1948). obtained. The lines associated with the 0.0574-Mev 3 H. B. Keller and J. M. Cork, Phys. Rev. 84, 1079 (1951). E. Kondaiah, Phys. Rev. 83, 471 (1951). 8 Hollander, Perlman, and Seaborg, Revs. Modern Phys. 25, 469 6 W. H. Burgus, Phys. Rev. 88, 1129 (1952). (1953). 182

183 DECAY OF RADIOACTIVE Ce148 (33.4 hr) X- RAY 143.294 Ce (33-hr).0574 COLLIMATED SINGLES LUIE 20-hr IRRADIATION iNo SOURCE w.145.351 -jr /1.493.6684 T a1031r~~~~ 7"65.861l I,.,)vI 1.10 I 10 I I II.1 I- 2 0.2 0.4 0.6 0.8 1.0 1.2 ENERGY IN MEV FIG. 1. NaI (TI) normal pulse-height distribution of Ce13 (33.4-hr) in "good" geometry. The geometrical arrangement is illustrated in the insert. The dashed curve is a portion of the pulse distribution of the single gamma ray (0.662 Mev) of Csm37 in the same geometry. transition are actually very intense, but the sensitivity other data. Only a single rather well-defined L-line is of the photographic emulsion varies rapidly with energy observed for the 0.0574-Mev transition, even though Mat low energies and causes some uncertainty. Estimates and N-lines are readily seen, and it appears definitely of the K/L ratio led to interpretations in conflict with to be the LI subshell line. The implications of this fact for interpretation of the transition character will be TABLE I. Gamma-ray and conversion-line energies in Mev. shown to be consistent with other data. For the gamma-gamma coincidence experiments, the Gamma e neergy sion-l Interpretation Energy su source was placed between two identical NaI crystals, Gamma energy energy Interpretation Energy sum which were about 2 inch apart. 900 mg/cm2 of Al was 0.0574+0.0002 0.0154 K 0.0574 placed in front of each counter to absorb the beta rays. 0.0505 Li 0.0575 0.0560 M 0.0574 Pulses from one of the counters were selected with a 0.0572 N 0.0576 single-channel differential analyzer and used to gate the 0.1416+L-0.0003 0.1036 K 0.1416 ten-channel analyzer. As no "fast" coincidence channel (Ce141) 0.1391 Li, 0.1415 was employed, the coincidence resolving time was 2X10-6 second. Rather low counting rates were used, 0.22450 K 0.2314 however, so that random coincidences were always negligible. In certain of the experiments, where one 0.294 +0.001 0.2522 K 0.2942 counter was observing low-energy events, and the other 0.287 L 0.294 0.293 M 0.294 high-energy events, 4 g/cm2 of lead was placed in front of the high-energy counter to intercept low-energy 0.351 +zi0.001 0.309 K 0.351 quanta scattering back to the low-energy counter. 0.493 +0.002 0.451 K 0.493 Curve B in Fig. 2 shows the spectrum of coincidence 0.48 L 0.49 pulses observed when the gating channel was set on the 0.565 +0.005 None 0.0574-Mev peak. Curve A is the ungated spectrum for the same geometry, and Curve C is the difference be0.668 +J=0.002 0.626 K 0.668 tween A and B for energies greater than 0.1 Mev. The 0.722 4-0.002 0.682 K 0.722 situation of the 0.0574-Mev peak in the total spectrum (see Curve A) is such that the gating channel is often actuated by pulses from the intense Pr x-ray peak at 1.10 +:0.01 None 0.036 Mev. These x-rays arise from internal conversion of all of the various gamma rays, and could therefore

MARTIN, BRICE, CORK, AND BURSON 184 o06 The spectra of Fig. 2 suggest that there exists a lowCe'43 (33-hr) lying state at 0.0574 Mev in the Pr'43 nucleus, to which AI A~ COINCIDENCE WITH 57.4 KEV all gamma rays in the decay lead except the four of lob XVS'hi | TRANSITION | energies 0.232, 0.351, 0.49351, 0 and 0.722 MIev. Of these, A-NORMAL -- |r.\ B-COINCIDENT the 0.351- and 0.722-Mev gamma rays appear from their \ C - NOT COINCIDENT energies to be crossovers for 0.294-0.0574 and 0.6810 4,I0 A 0.0574 cascades, respectively. These assumptions are _\ i \ consistent with all other data. Fm i) \ \~, \ \ Curve B in Fig. 3 is the spectrum of pulses in coinci<~~ 103lo~~ 1 1 \ At n | dence with the 0.294-Mev peak. To determine whether Z [ Gi \\! / \ the peaks at 0.565 and 0.81 Mev are gamma rays or 2o merely represent Compton scattering of higher energy, o \ de,0p - I gamma rays coincident with backscattered quanta of ~ \.', 0.29 Mev, various thicknesses of Pb were placed in 10" 04 0l g s,-*-front of the counter. The 0.565-Mev coincidence peak 0.2 0.4 0ENEROGY IN MEV 0.8 1.0.2 was attenuated by amounts characteristic of about 0.55 Mev and therefore represents a gamma ray, while the FIG. 2. NaI (TI) pulse-height distributions of Ce143 in coincidence geometry (see text). A. Ungated spectrum. B. Coincidence 0.81-Mev peak showed attenuations appropriate to 0.3 spectrum gated by the 0.0574-Mev peak. C. Difference between Mev and is thus due to backscattering. The upper A and B. portion of the spectrum as it appears through 4.1 g/cm2 of Pb is shown as Curve C in Fig. 3. give rise to peaks in the coincidence spectrum that are not in coincidence with the 0.0574-Mev transition. This TABLE II. Summary of gamma-gamma coincidence data. is undoubtedly the explanation for the x-ray and 0.0574- x: Coincidences observed; 0: coincidences not observed. Mev peaks in the coincidence spectrum. However, it is found in other experiments (see below) that, of all the Gamma-ray energy in Mev appreciably converted strong transitions (other than the 1.10 0.861 0.722 0.668 0.565 0.493 0.351 0.294 0.232 0.0574-Mev transition itself), none is strongly coincident ~ 0.0574 X X 0 X? 0 0 X 0 with anything of energy greater than 0.1 Mev. Thus, 0.232 0 0 0 0...... 0 0.294 0 0 0 0 X 0 0 virtually all coincidence pulses above this energy must t 0.351 0 0 0 0...... really be coincident with either the gamma quantum or E 0.493 0 0 0 0 -. the conversion x-ray of a 0.0574-Mev transition. 0.665 0 0 0 0 y 0.668 0 0 0 To verify these suppositions, the coincidence spec- 0.722 0 0 trum was observed with the gating channel moved from $ 0.861 0 the 0.0574-Mev peak to the x-ray peak. As expected, no changes were apparent in the region above 0.1 Mev. Virtually all x-rays coincident with the 0.294-M2ev peak must arise from internal conversion of the 0.0574t, -i 143o Mev transition. Therefore, comparison of the areas of l Ce (33-hr) the x-ray and 0.0574-Mev peaks in this coincidence COINCIDENCE WITH 0.294MEV 0 A I N TRANSITION spectrum provides a direct measurement of the K-shell A- NOR MA L internal-conversion coefficient of the latter transition. vJ ~\ \ B- COINCIDENT \ C- COINCIDENGE THROUGH The absorption efficiency of the crystal is 100% for both 4 4.1 gm/cm Pb peaks, but corrections must be made for the fluorescent / yield of Pr, the relative fractions of iodine K x-ray'.A' 0565 escapes, and the relative attenuations by beta absorbers Fm 1B3 - and light shields. The value obtained is aK= 5.9, with an,o 0 -._.... -..,:' ~03 —...-,?,/:Q \_,estimated uncertainty of less than ten percent.... \\ a In further experiments, the 0.232- and 0.493-Mev o if \2 peaks are found to be in coincidence. None of the four.o \peaks above 0.6 Mev are observed in a coincidence distribution in which the gating channel is set to accept 10' 0.2 0.4 0.6 0.8 1.0 1.2 all pulses corresponding to energies above 0.1 Mev. ENERGY IN MEV Table II summarizes the gamma-gamma coincidence FIG. 3. NaI(T1) pulse-height distributions of Cem' in coincidence data. An X indicates that coincidences are observed, geometry (see text). A. Ungated spectrum. B. Coincidence while a 0 indicates that coincidences were sought and spectrum gated by the 0.294-Mev peak. C. Same as B, through 4.1 g/cm2 of Pb. definitely not observed. Experiments that were not done

185 DECAY OF RADIOACTIVE Cel 4 (33.4 hr) are shown as... in the table. The 0.565-Mev peak was too weak to be seen in either the normal or 0.0574-Mev A-FERMI PLOT OF Ce'43 B-AFTER SUBTRACTION OF 1405 coincidence spectra, so a question mark is shown. C-AFTER SUBTRACTION OF 1125 C-AFTER SUBTRACTION OF 1125 III. BETA-RAY SPECTRUM, -ENLARGEMENT OF ENDPOINT Previous reports4,5 on the beta spectrum listed only 30 three resolved components, but suggested the probable N 3 existence of other lower-energy branches. The newly W discovered gamma rays, together with facts about the 2 level scheme deduced from the coincidence measurements, indicated that there must be two more com- 20 I ponents. A successful attempt to resolve them was made with the magnetic double-focusing spectrometer at the A University of Michigan. 1100 o100 1300 1400 Analysis of the spectrum is complicated by the \ presence of longer lived low-energy components due to xc 10 C m %0'"x,,_. XX 143 141 A Pr + Ce B C e4 xx 0 200 600 1000 1400 f \ E (kev). FIG. 5. Kurie plots of Ce's4 beta spectrum. A. Total composite lo-10~ \spectrum. B. Remainder after subtraction of 1.40-Mev component. C. Remainder after further subtraction of 1.125-Mev component. D. Enlargement of end-point region of A. three days. The second run was begun seventeen days I6 \: \later, and required thirteen days to complete because of the very low counting rates. 84 -B In order to make proper corrections for the long-lived components, the residual composite spectrum of the 2 ah >second run was resolved into its Pr'43 and Ce'4' com-.~ \ ~<~ponents. A Kurie plot using the Fermi functions and half-life characteristic of the Pr'43 decay yields a straight 0 200 400 600 800 1000 line with an end point of 0.934~0.01 Mev for the highestE (kev) energy component (see Fig. 4). The Kurie plot for the FIG. 4. Kurie plots of residual beta spectrum of Pr'43 and Ce'4' remainder, using the Fermi functions and half-life for components after decay of Ce'43. A. Composite spectrum. B. Remainder after subtraction of Pr'43. Ce'4', is also shown in Fig. 4. Although the plot suggests only a single component (except for considerable upward the daughter product Pr'43 and also Ce'41, the latter deviation below 150 kev), the data are not inconsistent representing initially about 2% of the activity. The with the reported6 two components of Ce'41. They are spectrum had to be remeasured after the Ce'43 had died not resolved here because of the very low counting rates out, to determine the contributions of these activities to associated with this activity in the source. the counting rates in the initial study. Total activity of The Pr'43 and Ce141 spectra were corrected for decay the sources was followed with an ionization chamber, and subtracted from the original data of the first run, and the results obtained over a 32-day period indicate after which the remainder was corrected for the 33.4-hr half-lives of 33.4 hours and 13.95 days for Ce'43 and decay of Ce'43. The Kurie plot is shown in Fig. 5 with the Pr'43 respectively. The half-life of Ce'4' was taken to be numerous internal-conversion lines at low energies the previously reported6 33.1 days, which was not omitted. verified here. In analysis of this complex Kurie plot, an allowed The source, which had been irradiated for 37 hours, shape is assumed for all components. This is consistent was mounted on a narrow strip of cellulose tape. The with the log ft values eventually determined, and with G-M counter was equipped with a Zapon window about the appearance of each component in the plot. However, 15 micrograms per square centimeter in thickness. The only the high-energy end of each one is seen because of initial run of the spectrum was begun about 24 hours the complexity of the spectrum. All straight-line fits are after the end of the irradiation, and covered a period of made by the method of least squares. The plot is re

MARTIN, BRICE, CORK, AND BURSON 186 points below 0.1 Mev still lie somewhat above the last A AFTER SUBTRACTION OF 740 straight line can probably be attributed to backscat8 AFTER SUBTRACTION OF 495 tering in the source. The errors quoted in Table III represent the statistical uncertainties in the leastt25 -squares fit. In the case of the lowest-energy component, N 25~~o the calculated statistical error was very small and was not believed to be significant after so many subtractions. 20 - \ ~xh A semiquantitative measurement of the beta rays in A coincidence with various gamma rays was made with the scintillation spectrometer. The beta rays were detected 5 Bi with an anthracene crystal 36 inch thick and 11 inches in diameter, coupled to an RCA 5819 photomultiplier. The pulse spectrum was examined with the ten-channel l0o ~ x \analyzer, gated by a NaI(TI) gamma-ray counter and \ 0o single-channel analyzer. The source, on a cellulose tape 5 x 00 backing, was placed between the two closely spaced counters and 900 mg/cm2 of Al covered the gamma counter as a beta shield. An Al foil of about 5 mg/cm2 thickness covered the beta counter as a light shield. 0 00 200 300 400kev An energy calibration and an indication of the performance of the spectrometer were obtained by exFIG. 6. Kurie plots of the two lowest energy beta components of amining the spectrum and the conversion line of Ce'43. A. Remainder after subtraction of 1.40-, 1.125-, and 0.74Mev components. B. Remainder after further subtraction of 0.50- Csl37, shown in the insert on Fig. 7. The beta spectrum Mev component. is seen to display a rather long straight section that extrapolates to zero at approximately the expected end solved into five components, as shown in Figs. 5 and 6 point, despite the fact that the curve trails off far beyond and listed in Table III. After subtraction of the rst two this end point. It appears from this, and is consistent components, the plot was a little ambiguous, and further with other experience, that spectra from this counter can analysis is based in part on independent information give rough estimates of end-point energies without that there is a component of around 0.7 Mev in coinci- correction for resolution, scattering, etc. No attempt is dence with gamma radiation (see below). The fact that made to deduce Kurie plots from these data. 181 16 C-17s CALIBRATION 143 14t \ { i\ (ABSCISSA Xj) Ce (33-hr) on \ ANTHRACENE PULSE DISTRIBUTIONS z 12 1 OF BETA RAYS o _ \ \ A-NORMAL,|, 10 _ \\ t 5625 kev IN COINCIDENCE WITH GAMMA RAYS o: \ \524 B- 0.0574 MEV e: C- 0.294 MEV 8 D- 0.668 MEV e~o6 \\~~~ 8.~ ~E- 0.861 MEV z F \ S;. F- I I0 MEV o 6w A A's (1 10: \F \ \K 0.30 0.54 0.73 MEV 1.11 1.40 FIG. 7. Anthracene pulse-height distributions of the beta rays of Ce'43. A. Normal or ungated spectrum. B-F. Coincidence spectra gated by gamma-ray pulses of energies: B. 0.0574 Mev; C. 0.294 Mev; D. 0.668 Mev; E. 0.861 Mev; F. 1.10 Mev. Insert shows the spectrum of Cs137 in the same geometry (abscissaXa). All curves normalized as coincidence counts per gamma count.

187 DECAY OF RADIOACTIVE Ce'43 (33.4 hr) Curve A of Fig. 7 is the ungated scintillation beta % -,,Ge 4333.4 hr) 1.46 spectrum of Ce'43, while curves B, C, D, E, and F are the 0.30 spectra in coincidence with the gamma-ray peaks of 6% 0.0574, 0.294, 0.668, 0.861, and 1.10 Mev, respectively. 1.16 The arrows indicating end points are placed in accord- 0.54 ance with the Cs"37 calibration. For the first three 1.10 components, the indicated end point is at the energy 0.918 determined by the magnetic spectrometer measure- 5% 0.861 ments, while for the last two they are placed at some- 0.565, 0.724 what higher energies as expected from the gamma-ray \.93 energies. 40% 0.668 It is evident that there really are five distinct com- \ \ 0.724 ponents, and that each is consistent (within the very 0.35 considerable uncertainties) with one of the expected 0.351 end points and the above extrapolation criterion. The I60 E2 (+MI?) 0.232 disagreement in the energies of the two lowest-energy 0.232 components between the magnetic spectrometer meas- 9, 0.0574 urements and the gamma-ray measurements cannot be * 3.95 doy)d 0.054 resolved from the scintillation spectra. Counting sta- Ml tistics are indicated for a few representative points in Fig. 7, and are seen to be very poor for the low-energy components despite counting times of several hours. Each component is seen without the presence of any 0.930 higher energy components so that no subtractions were 100% TABLE III. Summary of the magnetic spectrometer measurements of the beta rays. Beta-energy Intensity Spin Parity 60Nd's f t Isotope (Mev) (%) Logft change change (STABLE) Ce'4' 1.40 -0.02 37 7.75 0,1 yes FIG. 8. The decay scheme of Ce'43 (33.4-hr). Ce14a 1.125~-0.015 40 7.30 0,1 yes Ce'4' 0.74 +0.15 5 7.7 0,1 yes particular interest were the not-fully-resolved gammaCe'4' 0.50 ~-0.03 12 6.6 0,1 yes Ce'43 -0. 03 12 65.8 0,1 yes orno ray pairs 0.294-0.351 and 0.668-0.722 Mev. In each Pr'43 0.93 +0.01 100 7.60 0,1 yes case the compound peak was observed to absorb out without change of shape, indicating that its two component gamma rays originate from the same level. required. This is due to the very fortunate circumstance that if a given beta ray and gamma ray are in coinci- IV. CONCLUSION dence, all higher-energy beta rays are coincident only The given data all support the decay scheme shown in with lower energy gamma rays. Some slight gamma- Fig. 8. There is some inconsistency concerning the gamma background is indicated in the last two curves, energy of the lowest energy beta-ray component, in that E and F, but is entirely negligible in all the others. the gamma-ray energies require that the beta ray have The normal and 0.0574-Mev coincidence distributions an energy of 0.30 Mev, while the magnetic spectrometer (Curves A and B) merge together above the end of the analysis indicated a value of 0.22 Mev. The discrepancy next lower component (Curve C). Careful examination is not regarded as serious since the accumulated errors of of this region of the spectrum with good statistics shows the many subtractions in the latter analysis must be no detectable differences. The 1.40-Mev component very considerable. The energy of the 1.10-Mev gamma evidently proceeds to the 0.0574-Mev level, and it can ray, on the other hand, was measured with reference to be asserted that there is no slightly higher energy the 1.17-Mev line of Co60, and is believed to lie within branching to the ground state of intensity more than a the quoted uncertainty. few percent of the 1.40-Mev branch. The relative order of the 0.493-0.232 Mev cascade In one further coincidence experiment, the gamma- was not determined in this study. The excellent agreeray spectrometer was gated by the beta counter. The ment of this energy sum with the 0.722-Mev gamma ray behavior of various gamma-ray peaks was observed as leaves little doubt that the cascade does come from this the coincident beta rays were attenuated with aluminum level, however. No other position would be consistent absorbers. In every case the coincidence rates were with the gamma-gamma coincidence data. observed to fall off with half-thicknesses of Al consistent The value of the K-conversion coefficient (5.9), the with other measurements of the beta-ray energies. Of predominance of the LI subshell line in the L-conversion,

MARTIN, BRICE, CORK, AND BURSON 188 and the lifetime (less than the resolving time of the undergo a first-forbidden beta transition equally well to coincidence circuit, 2X10-6 second) of the 0.0574-Mev either of the possible choices for the ground state of transition are all consistent with an M1 interpretation. Pr143, whereas the ground-state transition is not obLack of exact theoretical values for aK does not permit served. If it were h9/2, however, decay to a g7/2 state in exclusion of some E2 admixture, but the lack of an Pr is only first forbidden, but decay to a d5/2 state is observable LII conversion line limits this possibility to a "I-forbidden" with Al= 3. This assignment is therefore few percent. consistent with observation, if the Pr143 ground state is The measured K/L ratio of the 0.294-Mev transition identified as d5/2. Then the 0.0574-Mev excited level can indicates several possibilities. M3 can be excluded be- be g7/2, consistent with the M1 character of the gamma cause the life of this state is also less than the resolving transition. time of the coincidence circuit. M2 or El interpretations Although it is indicated above that the 0.294-Mev are inconsistent with the plus parity of the 0.351-Mev state indicated by the beta-ray measurements. The transition appears to be E2, the fact that the 0.351-Mev state indicated by the beta-ray measurements. The remaining choice is E2. crossover is seen makes it seem unlikely that the 0.351remaining choice is E2. According to the single-particle model, the ground /Mev level has a spin as great as 11/2. It is tentatively state of Pr143 (59 neutrons) may be d5/2 or g7/2. Either suggested that this is a g9/2 state, and that there may be assignment is consistent with the observed character of some M1 admixture in the 0.294-Mev transition. the beta transition to Nd143, which has a measured spin6 V. AC of 7/2 and is f7/2 (83 neutrons). The ground state of Ce143 (85 neutrons) may be f7/2 or h9/2. The f7/2 assign- Thanks are expressed to Dr. J. M. LeBlanc and Dr. ment is unsatisfactory since the state could then E. L. Church for many valuable discussions.

II RADIATIONS FROM THE ACTIVE ISOTOPES OF YTTERBIUM

Reprinted from THE PHYSICAL REVIEW, Vol. 101, No. 3, 1042-1046, February 1, 1956 Printed in U. S. A. Radiations from the Active Isotopes of Ytterbium* J. M. CORK, M. K. BRICE, D. W. MARTIN, L. C. SCHMID, AND R. G. HELMER University of Michigan, Ann Arbor, Michigan (Received August 15, 1955) By using Yb of high purity (99.8%) irradiated in the maximum flux of the Argonne pile and studied by scintillation and magnetic photographic spectrometers, a reevaluation of the energies of the radiations has been made. Several previously unreported gamma rays are found and nuclear level schemes for Tm'69, Lu"76, and Lu'77 are proposed. Several of the levels appear to be rotational states in the unified nuclear model. Yb'69 decays with a half-life of 30.6 days by K capture, followed by eleven gamma rays in Tm'69. Rotational levels lie at 8.4, 118.3, and 139.1 kev. The gamma energies are 8.4, 20.6, 63.2, 93.6, 109.9, 118.3, 130.7,'177.7, 198.6, 261.0, and 308.3 kev. Yb'76 decays with a half-life of 4.2 days by, emission (471 kev max) followed by five gamma rays in Lu'76. Rotational levels exist at 114.1, and 251.9 kev. The gamma energies are 114.1, 137.8, 145.0, 282.9, and 397.0 kev. Yb'77 decays with a half-life of 1.88 hour by, emission followed by gamma transitions in Lu'77. In addition to any lower energy gamma rays, two high-energy transitions are found at 1.080 and 1.228 Mev. The latter is a cross over for the 1.080- and 0.148-Mev gammas which are in coincidence. The expected well-known daughter product Lu'77, if present at all, is too weak to be observed by the magnetic spectrometers. YTTERBIUM exists in nature as seven stable magnetic photographic and scintillation spectrometers. isotopes, with masses ranging from 168 up to 176, The beta spectrum of Yb'75 was observed in the doubleexcept for 169 and 175. Neutron capture might be focusing magnetic spectrometer. Studies of the shortexpected to produce radioactive Yb'69, Yb'75, and Yb'77. lived (1.88 hour) activity were made on spectrometers Previous studies have been made'-3 on these activities located adjacent to the pile. with some disagreement in reported results. Since Yb Due to the very great source strength, spectrograms samples of high purity (99.8%) are now available could be obtained with exposures of a few hours, with exand the neutron flux density in the pile is much greater cellent geometry. Some sixty electron conversion lines than was used in the earlier irradiations, a reinvesti- were observed and measured. The electron lines apgation of the radioactivities seemed worthwhile. peared to belong to two distinct groups as judged by their Specimens were irradiated in the maximum flux half-lives and their K-L-M energy fits. One group satisregion of the Argonne pile and were studied in both fying the work functions of Tm (Z= 69) decayed with a half-life of 30.6 days. These transitions are believed to TABLE I. Conversion electron energies due to transitions in occur in Tm'69 following K capture in Yb'69. Since Yb'68 is Tm (Auger lines omitted) in kev. not abundant (0.14%) in normal Yb, it must have a very large capture cross section to produce the high Electron Interpre- Energy Electron Interpre- Energy yield of Yb169. The energies of the electron lines that energy tation sum energy tation sum 6.1g tatio 8.4 101.1y L 1098 decay with the 30.6-day half-life, exclusive of those of 7.9 N 8.4 107.5 M 109.8 Auger origin, are presented in Table I. The interpre10.5 L, 20.6 108.7 L2 118.3 tation of these lines confirms the existence of eleven 18.3 M 20.6 109.5 N 110.0 gamma rays. Certain of these (8.4 and 261 kev) had 20.3 N 20.8 118.3 K 177.7 34.2 K 93.6 120.4 L1 130.5 not been observed before. Some gamma rays previously 50.5 K 109.9 120.9 L2 130.5 reported3 could not be found, particularly those of 53.0 L1 63. t 121.9 L3 130.6 energy 142.6 and 160 kev. Conversion lines attributed 53.5 L2 63.1 128.6 M 130,9 54.5 L3 63.2 130.4 N 130.9 to these gamma energies are otherwise interpreted. 58.9 K 118.3 139.4 K 198.8 Table II shows the energies of the gamma rays to60.9 M 63.2 175.6 L, 177.7 gether with their K/L ratios and the relative intensities 62.7 N 63.2 175.2 M 177.5 71.3 K 130.7 176.9 N 177.4 of the L lines, where observable. The no-screen photo83.6 L1 93.7 188.4 L 198.5 graphic emulsion appears able to record energies as low 83.9 L2 93.5 196.0 M 198.3 84.7 L3 93.4 198.0 N 198.5 as 5 kev. The lowest energy gamma ray (8.4 kev), 91.3 M 93.6 201.6 K 261.0 which is of considerable theoretical interest, can 93.1 N 11093.6 248.7 308.1 energetically yield on conversion only M and N 99.9 L1 110.0 298.2 L, 308.3 100.2 L2 109.8 306.4 M 308.7 electrons. These observed electron lines at 6.1 and 7.9 kev are believed to be not of Auger origin because of their sharpness. The relative intensities of many of the * This work was supported jointly by the Office of Naval electron lines were determined from microphotometer Research and the U. S. Atomic Energy Co~mmission. electron lines were determined from microphotometer Research and the U. S. Atomic Energy Commission.'Cork, Keller, Rutledge, and Stoddard, Phys. Rev. 78, 95 traces of the photographic plates. Corrections were (1950). made for varying radius and emulsion sensitivity with 2 A. Sunyar and J. Mihelich, Phys. Rev. 81, 300 (1951). 3 Martin, Jensen, Hughes, and Nichols, Phys. Rev. 82, 579 energy. In some cases only a visual estimate could be (1951). made of the relative intensities. 1042

1043 RADIATIONS FROM ACTIVE ISOTOPES OF Yb Since most of the gamma rays enter into coincidence with others, and with Tm x-rays, the lifetimes of all 50 unstable levels must be short. A comparison of the 1 115 observed line intensities with the calculated internal conversion coefficients of Rose et al.4 for the K, L1, and L2 shells and with the relative conversion coefficients for the L3 subshell given5 by Church and Monahan, makes possible an assignment of multipolarities for most of the gamma rays. Where the ratio of intensities for the L lines was not supported by the K/L ratio, in making an assignment of multipolarity, less weight was given to the latter because of the large and somewhat al uncertain variation in emulsion sensitivity with energy. 51 The preferred assignments of multipolarity are shown t in column 6 of Table II. It appears in several cases that 190 the observed intensities can best be satisfied by a 263 mixture of M1 and E2 radiations, although for the 317 63.2-, 93.6-, and 109.9-key' transitions the possibility of an El assignment cannot be eliminated on the basis of the relative line intensities alone. 190 115 TABLE II. Gamma energies in Tm169 with intensities and multi- 20 polarities. (The symbol x indicates that only one L line was observed.) 308 Gamma Rel. intensity Multikev K/L Li L2 L3 polarity 0 to 20 30 40 50 8.4 VVOLT S 20.6. x M 63.2 10 4.3 5.l5 M FIG. 1. Scintillation spectrometer peaks; A-singles, 93.6 1.62 0.2 10 1.8 1.0 M1, E2 B —source in crystal well. (Energies in kev.) 109.9 2.9~-0.3 10 1.9 0.6 M1, E2 118.3 0.9~-0.3 x E2 130.7 0.8+-0.2 [ 10' 9 E2 261, or 308 kev. With good geometry the 308-kev peak 177.7 5.6i0.2 x M1, E2 is found in coincidence only with the 50-kev peak. On 198.6 6.6~0.2 x M1, E2 the other hand, with 27r solid angle a coincidence peak 261.0 308.3 3.54-0.2 [ x ] E2 appears at 115 kev which is attributed to summations —: __________________; between thulium x-rays and the 63-kev gamma. When the source was placed in a narrow well in the NaI Although the resolution of the scintillation spectrom- crystal so as to give summation effects, the 20-kev peak eter is not comparable with that of the magnetic instru- disappeared and the 50- and 190-kev peaks were lesments, important information on coincidences and sened in height while those at 115, 261, and 308 kev summations was obtained with it. A single crystal were augmented as shown in Curve B, Fig. 1. yields the distribution shown in Curve A of Fig. 1, A nuclear level scheme for Tm'69 is presented in Fig. indicating six peaks, some of which are composite. A 2. The spin of the ground state for the odd-A (Z= 69, coincidence curve with thulium x-rays (50 kev) is N= 100) nucleus has been measured to be 1/2. This is identical in shape with the singles curve. A similar interpreted from the shell model as an s1 state. Some result is obtained with the fixed channel set on 20 kev. calculations of the low-energy gamma rays to be exSince there exists the possibility of back-scattered iodine pected in Tm'69, assuming them to be transitions x-rays (29 kev) from the crystal and the subsequent between rotational states in the unified nuclear model, escape peaks of the thulium x-rays, the above simi- have been made by Mottelson and Nilsson.6 Their larity in results is not unexpected. The high-energy side expression for the energy El in terms of the spin I is of the 115-kev peak (130.7) was found to be in coinciE,= (h2/2J){I(I+ 1)+ a(- 1)I+i(1I+~)}, dence with the low-energy side of the 190-kev peak (177.7). The 261-kev peak was in coincidence with the where J is the moment of inertia and a is a constant as 110 or 118 or both but not with the peaks at 130, 190, I takes values 1/2, 3/2, 5/2, 7/2, 9/2, etc. Using the tvalues for thvalues 1/2, 3/2, 5/2, 7/2, 9/2, et. Using thensen 4Rose, Goertzel, and Perry, Oak Ridge National Laboratory Report No. ORNL-1023, 1951 (unpublished); and subsequent et al., which are somewhat in error, they derived a value letters. 6 E. L. Church and J. E. Monahan, Phys. Rev. 98, 718 (1955). 6 B. R. Mottelson and S. G. Nilsson, Z. Physik 141, 217 (1955).

CORK, BRICE, MARTIN, SCHMID, AND HELMER 1044 70 yb1699 500 -''69 O,00oo 7 950 0638.230 MI+E293. from the suation evidence that the 316.8-ke level 26L0,383 ose0 appears to be 30 40ke 50 60 70 reasonable since MI+E29I I+E2 FIG. 3. Analysis of the decay curve for Yb. -~ [ 206 from the summation evidence that the 316.8-key level I [ MI is most likely the delayed state. The presence of an ( 0.7 118.+) T3 unsummed x-ray peak strongly suggests a K-capture FIG. 2. Nuclearlevsbranch terminating at this level. The highest summation 09.9 level appears to be 317 key, which is reasonable since Mand+E2 1 the transitions above it could not be included because Epar of the delay. The increased peak height at 115 keg could *aL~ 8.4 8.4 be due to the sum of 63 kel and the x-rays (50 ket). (o ~) The placement of the strongly converted 93-key gamma (2, 2, transition is based on the augmented peak at 263 kev FIG. 2. Nuclear level scheme for Tm'6a following K capture in which could be the sum of 118, 93, and 50 kev. Yb'6a. (Energies in key.) Spin along axis of symmetry, total spin, Th level at 211.9 ke is expected to be a single and parity are shown in parentheses. particle state, which may be either d5/2 or g7/2 in agreement with the shell model and the Mi character of the of the first three levels (8.4, 118.3, and 139.1 key), a is a single-particle level. It is observed that if this level is obtained by comparing each of the upper energies with a sinl-rieev.Ii o bserved th at if thi lve is the lowest. Its value is found to be -0.775 and the assigned a spin of 3/2 and the moment of inertia is assumed to be the same as in the ground state, the first excellent agreement between calculated and observed rotational excitation will come 62.2 kev higher, as energies for the first three levels is shown in Table III. compared with the observed transition of 63.2 kev. The lack of agreement for the two higher spins indicates An analysis of the rate of decay shown in Fig. 3 that these possible rotational levels are not observed. indicates half-lives somewhat different than previously Since the rotational levels are of the same parity, short- found.' This must be due to the higher purity of the lived transitions between them can be only M1 or E2 Yb specimen. The long half-life of Yb'69 appears to be in nature, in agreement with the multipolarity assign- 30.6~0.2 days. The previously reported intermediate ments noted in Table II. From the results with the source in the crystal well,;upport.s obtained for the arrangement of levels as TABLE IV. Conversion electron energies in kev in Lu'76 support is obtained for the arrangement of levels as following / emission from Yb75. shown in Fig. 2. A metastable level of half-life 6X 10 —7 second had been observed2 in Tm169 and it was believed Electron Energy to be derived from K capture directly. It now appears energy Interpretation sum 50.5 K 113.8 74.5 K 137.8 TABLE III. Energies in kev of rotational levels, 81.7 K 145.0 together with observed energies. 103.1 LI 114.0 103.6 L2 114.0 I Calculated Observed 104.9 L. 114.1 111.7 ilM 114.2 3/2... 8.4 113.5 N 114.0 5/2 118.8 118.3 127.3 L1 138.2 7/2 138.6 139.1 219.6 K 282.9 316.8 272.6 L2 283.0 9/2 337 333.5 K 396.8 11/2 368 386.5 L 397.4 380.0 394.9 M 397.4

1045 RADIATIONS FROM ACTIVE ISOTOPES OF Yb half-life of 6.7 days attributed to Lul77 could not be observed. For Yb'75 the half-life is 4.240.1 days. The absence or extreme weakness of the 6.7 day Lul'77 activity as noted both in the decay curves and in the lack of conversion lines for the well known gamma transitions in Hf raises a serious question. The previous observation of the rather strong activity must have been due to Lu being present in the Yb as an impurity. Since Yb176 is abundant (12.7%o) in all Yb, it is difficult to understand why Yb'77 with its half-life of 1.88 hours would not build up the Lu'77 daughter activity. Either the capture cross section in Yb'76 is':. very small, which does not appear to be the case, or some assignment of mass may be in error. 1,75 175 70 1Yb05 -, 7Lu, \7I 1397.0' \ ~~~471\~~ ~~145.0 4:1 397.0 E2 282.9. \ \ Ml+~2 0 100 200 300 400 500 ENERGY (KEV) ( t+) I I T~ — 251.9 FIG. 5. Kurie plot of the i3 spectrum of Yb75. 137.8 MI+E2 values for the 138- and 283-kev transitions are based upon visual estimates of the blackness of the lines. The choice of M1, E2 for the 114-kev gamma is based upon (9,1,4+) i the agreement with calculations4 for the L1/L2 ratio, i ~ and is supported by agreement with the empirically 114.1 expected'0 K/L ratio. To satisfy the observed K/L ratio MI+E2 and the presence of a strong L2 line for the 283-kev gamma a mixture of E2 and M1 transitions also appears 7T At) - 1 O likely. The other selections are based upon the K/L X,,+) a ratios together with the assumption of very short lifeFIG. 4. Nuclear level scheme for Lu'76 followings emission times. A nuclear level scheme for Lul'7 based upon from Yb'76. (Energies in key.) excellent energy fits is presented in Fig. 4. The spin of the ground state in Lu 75 has been measThe electron conversion lines that decay with the The electron conversion lines that decay with the ured to be 7/2, which from shell theory is interpreted 4.2-day half-life are shown in Table IV together with their interpretations. It appears without doubt that If the lower energy levels are regarded as rothere are five gamma rays, whose energies and relative conversion intensities are presented in Table V. This TABLE: V. Gamma energies in kev in Lu'75 and relative electron line intensities. (The symbol x indicates that only one L line was is in agreement with the recent results7 of Mize, Bunker, observed.) and Starner on Yb'75. Only one of these gamma rays (114 kev) is observed8 in the decay of Hf'75. In the Gamma MultiCoulomb excitation of Lu'75 both of the levels 114 and energy K/L Li L2 L polarity 252 kev are found to exist.' The K/L ratios for the 114- 114.1 2.94-0.4 10 4.1 2.7 Mll, E2 137.8 -.2 E2 and 397-kev gammas were determined from micro- 145.0 photometer traces of the photographic plates. The 282.9 -.-,6 x M1, E2 397.0 5.4:=0.3 E2 7 Mize, Bunker, and Starner, Phys. Rev. 99, 671 (1955). 8 Burford, Perkins, and Haynes, Phys. Rev. 99, 3 (1955). 9 G. Temmer and N. Heydenburg, Phys. Rev. 94, 1399 (1954).'o M. Goldhaber and A. Sunyar, Phys. Rev. 83, 906 (1951).

CORK, BRICE, MARTIN, SCHMID, AND HELMER 1046 TABLE VI. Relative intensities of the K-L-L auger lines. K-LI-LI K-LI-Lnx K-LI-LIrI K-LIi-LII K-LnI-LnI K-LIII-LIIx Observed 1.0 1.6 1.5... 2.0 0.9 Calculateda 1.0 1.02 1.65 0.24 1.46 0.81 ^ See reference 13. tational in nature, then their energies may be calculated kev level is in agreement with the angular correlation from that of the gamma ray of lowest energy. As the work of Akerlind et al."n spins are given successive values of 9/2, 11/2, etc. and The beta spectrum of Yb'75 was observed with the the 114-kev gamma regarded as basic, then the fol- double-focusing magnetic spectrometer, using a Scotch lowing levels should have energies of 253.6 and 418.5 tape source and Zapon (-15 micrograms per square kev. The 253-kev value is in good agreement with an centimeter) counter window, with a resolution of 0.5o%. experimental level, as shown in Fig. 4. The level at 397 The Kurie plot is shown in Fig. 5. The spectrum appears key is sufficiently divergent from the expected 418-key to be complex, with an upper energy limit of 471~3 kev. value, to assume that it is not rotational. The transitions After subtraction of this high-energy component, there between the rotational levels, with no change in parity, is found to be a rather large scatter in the points of the should be M1 or E2 or a combination of both, agreeing residual Kurie plot. A least squares fit to these points with the choices indicated in Table V. The 397-kevy level in regions where no interference from internal conis expected to be a single-particle state. The multi- version lines is expected gives a component of maximum polarities of the various gamma rays, together with the energy 374~t30 kev, whose intensity is about 25% that fact that the energy available in beta decay will permit of the high-energy component. The level scheme reat most an ordinary first forbidden transition, suggest quires an additional low-energy component at about that this level has spin 9/2 and even parity, with an 80 kevy, which would be difficult to observe due to the f7/2 ground state for Yb'75. The spin of 9/2 for the 397- many internal conversion lines in this region. The activity in Ybl77 was induced by short irradiation 177 in the maximum flux region of the pile and was studied 70Yb107 in a ten channel scintillation spectrometer and magnetic (.88H) photographic spectrometer near the pile. A recent paper reports'2 the existence of two gamma rays of energy 119 and 146 kev and three beta rays with a maximum energy of 1.3 Mev. In the present investigation two 177Lu additional high-energy gamma rays are found with 7-U106 energies of 1.228+0.005 and 1.080~i0.005 Mev. The,\ \ -1.228 former is undoubtedly a cross-over transition for the 1.3 \1.080- and 0.148-Mev gammas which are found to be in coincidence. All gamma rays appear to decay with a \, \ half-life of 1.88~0.1 hr. The gamma ray reported at 119 kev has not been identified but is included as a \ \ I.c080 L228 dotted line in the provisional level scheme shown in'\ I\ Fig. 6. It has previously been assumed that the ground state of Lu'77 has a half-life of 6.7 days followed by the emission of certain well-known highly converted gamma rays in Hf'77. It is quite certain that this activity, if present at all, is extremely weak in the high-purity Yb source. Auger electrons following K-capture to Tm'69 were -0.148 also observed. Their relative intensities, determined -|l9 from microphotometer traces of the photographic plates, 0.11 Q1I48 are presented in Table VI, together with the calculated Io? r,intensities of Hill'3 for Z= 80. - 0 11 Akerlind, Hartmann, and Wiedling, Phil. Mag. 46, 448 (1955). FIG. 6. Nuclear levels in Lu77 following 5 emission in 12 H. deWaard Phil. Mag. 46, 445 (1955). Yb'77. (Energies in Mev.) 13 R. D. Hill, Phys. Rev. 91, 770 (1953).

III DECAY OF Ca49 AND Sc49

Reprinted from THE PHYSICAL REVIEW, Vol. 102, No. 2, 457-458, April 15, 1956 Printed in U. S. A. Decay of Ca49 and Sc49t D. W. MARTIN, J. M. CORK,* AND S. B. BURSON Argonne National Laboratory, Lemont, Illinois (Received January 6, 1956) Ca49 has been found to decay with a half-life of 8.94-0.2 minutes. It emits two principal beta components of energies 2.124-0.10 and about 1.0 Mev in coincidence, respectively, with gamma rays of 3.0740.05 and 4.044-0.06 Mev. The intensity ratio of these two branches is 8.5: 1. The intensity of a possible ground-state beta branch is less than 1%, and that of a possible 0.98-Mev gamma transition between the 3.07and 4.04-Mev levels is less than 3%. These data indicate that these excited states are respectively the single-particle pi and fi levels available for excitation of the twenty-first proton in SC49. Sc49 is found to emit in turn a single beta component of energy 1.804-0.10 Mev. I. INTRODUCTION A very recent report4 has verified that this is indeed TTNTIL recently little was known of the decay of the case. Two gamma rays of 3.10 and 4.05 Mev were Ca49 except for a reportl that it emitted beta rays observed with intensities in the ratio 9.0:1. This is consistent with the belief that the excited states from of 2.7 Mev with a half-life of 8.5 min. The daughter Sc4 consistent with the belief that the excited states from has been reported2 to emit a single beta ray of 2.00 Mev which they originate are the pt and f1 levels respecwith a half-life of 57 min. The decay of Ca49 seemed tively, while the ground state is f7/2. One additional to be of particular interest from the point of view of gamma ray was observed at 4.68 Mev with intensity the single-particle model since the daughter Sc49 nucleus indicating that 0.38% of the decays passed through the has a closed shell of 28 neutrons and one proton outside corresponding level. There was found to be no direct the closed shell at 20. Beta-decay systematics' indi- beta transition to the ground state. The highest energy cated that there should be about 5 Mev of energy beta component, leading to the 3.10-Mev excited state, available for the decay. It seemed possible that one was reported to be 1.95 Mev, giving a Q-value for the might see in this case the relatively pure single-particle decay of 5.05 Mev. The half-life was reported to be excited states available to the twenty-first proton and 8.75 min. The daughter SC49 was found to decay expected to lie 3 Mev or more above the ground state. with a period of 57.2 min and emit a single beta ray of 2.05 Mev.5 t This work was carried out under the auspices of the U. S. Atomic Energy Commission. 40'Kelley, Lazar, and Eichler, Phys. Rev. 102, 223 (1956). * University of Michigan, Ann Arbor, Michigan. 6 Note added in proof.-See also M. McKeown and G. Scharff1E. der Mateosian and M. Goldhaber, Phys. Rev. 79, 192 Goldhaber, reported in Nuclear Level Schemes A =40-92, edited (1950). by K. Way et al. (U. S. Atomic Energy Commission Report' L. Koester, Z. Naturforsch. 9a, 104 (1954). TID-5300, 1955). A gamma ray of 3.00 Mev is reported to be in' K. Way and M. Wood, Phys. Rev. 94, 119 (1954). coincidence with a beta ray of 2.0 Mev.

458 MARTIN, CORK, AND BURSON oa49 the several peaks associated with these two gamma rays 20 29 49 P,Sc P yielded no pulses above the random coincidence rate 8.9mm in <P P0 5 other than those due to annihilation quanta and back\q...... scattered Compton quanta. In particular, the intensity of a possible 0.98-Mev gamma ray in cascade with the 2.12 3.07-Mev radiation does not have an intensity in excess P\ I p of about 3/0 of the latter. 4.7 5.9~0.l2 Beta-gamma coincidence absorption curves were ob) 0.8% MEV tained in which the beta rays were detected by an I % anthracene crystal. Beta rays of 2.124-0.10 Mev were 3.0 7 found to be coincident with the 3.07-Mev gamma ray, 89% and others of about 1.0 Mev were in coincidence with i7mm l lthe 4.04-Mev gamma ray. The source was left undis57min ElI f - turbed until the Ca activity had disappeared, after which the absorption curve of the beta rays of the Sc49 1.80 Ti" daughter was obtained. The result gave an energy of 2211< 2 P.T, 7 1.8040.10 Mev. The discrepancy between these results f 7/1" and those of O'Kelley et al.,3 in the relative energies of FIG. 1. Decay scheme of Ca49 and Sc49. the Sc and Ca beta rays is well outside quoted errors. Anthracene pulse distributions of the beta rays were Simultaneous independent studies at this Laboratory in qualitative agreement with the absorption results. have led to results in essential agreement with the above, these distributions, the intensity of a possible 5.2-Mev ground-state beta branch can be asserted to except for some discrepancy in the beta-ray energies. 5.2-Mev ground-state beta branch can be asserted to be less than one percent. Logft values deduced from The improved results obtained since our preliminary report. are briefly summarized below. this fact and from the gamma-ray intensities indicate that all three transitions to the 3.07-, 4.04-, and 4.7-Mev II. EXPERIMENTAL RESULTS levels are allowed, while the ground-state transition is - gaamm1. at least 2nd forbidden. Also, the Sc beta transition is The. gamma.-ray spectrum was studied usig,,4-ih allowed. All these statements are fully consistent with cubic NaI(T1) crystals and the Argonne 256-channel cubic NaI(T) crystals and the Argonne 256-channel the level assignments shown in Fig. 1. The assignments pulse-height analyzer. The spectrum observed in a wellshown are just those predicted by the single-particle collimated arrangement indicated only two gamma rays model, and are identical with those of O'Kelley et al.3 of energies 3.074-0.05 and 4.04I4-0.06 Mev and intensity The lack of a strong 0.98-Mev transition between the ratio 8.5: 1. The 4.68-Mev gamma ray reported by ratio, 8.5:1. The 4.v g a ry 4.04- and 3.07-Mev levels indicates that their assignO'Kelley et al.,3 was at first overlooked, but on closer ments cannot be interchanged. Crude single-particle examination the data are consistent with its existence. ments cannot be interchanged. Crude single-particle estimates7 of transition probabilities predict that a Our data indicate an energy 4.74-0.1 Mev and an in- transition t 0.98-Mev M1 transition would be several times as tensity representing 0.8%/ of the decays. The entire pulse spectrum was found to decay with a half-life of probable as a 4.04-Mev E2 transition. 8.9~-0.2 minutes, except for a low-energy continuum The Q-value of the decay obtained from our results is due to Sc bremsstrahlung. Calibration was based on the 5.19~0.12 Mev. 4.45-Mev gamma ray of a Po —Be source, and on the Thanks are expressed to Dr. O'Kelley, Dr. Lazar, gamma rays and sum peak of Na24. and Dr. Eichler for communication of their results in Pulse distributions taken in coincidence with each of advance of publication. 6 Martin, Burson, and Cork, Phys. Rev. 100, 1236(A) (1955). 7 V. F. Weisskopf, Phys. Rev. 83, 1073 (1951).

IV RADIOACTIVE DECAY OF TERBIUM-161

Reprinted from the Bulletin of the American Physical Society, Series II, Vol. 1, No. 6, 297, June 21, 1956 Radioactive Decay of Terbium-161. J. M. CORK, M. K. BRICE, L. C. SCHMID, AND R. G. HELMER, University of Michigan. —A specimen of Gd160 enriched from its normal 21.9% up to 95.4% was irradiated in the heavy water pile for a week. The'Gd161 formed by neutron capture decays by beta and gamma emission with a half-life of 3.7 min to radioactive Tb161. Spectrometric studies of this activity show it to decay with a half-life of 7.15 days emitting both beta and gamma rays most of which have previously not been evaluated. The gamma rays are highly converted as evidenced by some forty electron conversion lines. Using the work functions for Dy there appear to be eight gamma rays whose energies are -25.6, 27.7, 48.9, 57.3, 74.8, 78.3, 106.2, and 132.1 kev. These energies fit remarkably well in a scheme with nuclear levels at 25.6, 74.8, 104.0, and 132.0 kev. Coincidence data with the scintillation spectrometer support the proposed plan. The beta spectrum appears to be composite with a maximum energy at 540 kev for which the log ft is about 6.6.

V DECAY OF Mo (14.6 min)

Reprinted from the Bulletin of the American Physical Society, Series II, Vol. 1, No. 7, 329, November 23, 1956 Decay of Mol~1(14.6 min).* D. W. MARTIN AND S. B. BURSON, Argonne National Laboratory, AND J. M. CORK, University of Michigan.-The radiations emitted in the decay of 14.6-min Mo10' have been studied with the Argonne 256channel coincidence scintillation spectrometer and with magnetic spectrographs. Ten major gamma rays of 0.080, 0.191, 0.510, 0.590, 0.704, 0.890, 1.024, 1.18, 1.56, and 2.08 Mev can be resolved in the normal spectrum. In coincidence experiments, evidence is obtained for at least twelve additional weaker transitions of 0.193, 0.300, 0.40, 0.51, 0.70, 0.84, 0.95, 1.14, 1.28, 1.38, 1.46, and 1.66 Mev. At least six distinct beta components of about 2.2, 1.6, 1.2, 0.8, 0.7, and 0.6 Mev can be discerned in beta-gamma coincidence experiments. The beta component of highest energy is in coincidence with the 0.590Mev gamma ray. The strong 0.191-Mev gamma transition is not in prompt coincidence with beta rays; the half-life of the upper state has been determined to be about 9.1 X 10-4 sec. The K-conversion coefficient of this transition is 0.304-0.06. The probable character is therefore M2 or E3, with no possibility that it can be M4. A decay scheme is proposed that is compatible with all the many gamma-gamma and betagamma coincidences observed and with the estimated intensities of all components. The scheme involves eleven excited states of Tc10l at 0.191, 0.510, 0.590, 0.70, 0.84, 0.89, 1.21, 1.59, 1.98, 2.08, and 2.16 Mev. The ground state is probably g9/2. * Work performed under the auspices of the U. S. Atomic Energy Commission.

VI NUCLEAR LEVELS IN Dy161

Reprinted from THE PHYSICAL REVIEW, Vol. 104, No. 2, 481-483, October 15, 1956 Printed in U. S. A. Nuclear Levels in Dy16t J. M. CORK, M. K. BRICE, L. C. SCHMID, AND R. G. HELMER University of 71ichtigan, Ann Arbor, Michigan (Received June 6, 1956) A specimen of Gd160 enriched from its normal 21.9% up to 95.4% was irradiated in the Argonne heavy water pile. The Gd16' formed by neutron capture decays by beta and gamma emission with a half-life of 3.7 min to radioactive Tb"l'. Spectrometric studies of this activity show it to decay with a half-life of 7.15 days emitting both beta and gamma rays many of which previously have not been evaluated. There appear to be seven gamma rays in Dy, all internally converted, whose energies are: 25.6, 27.7, 48.9, 57.3, 74.8, 78.3, and 106.2 kev. These energies fit into a scheme with nuclear levels at 25.6, 74.8, 103.9, and 132.0 kev. Coincidence data with the scintillation spectrometer support the proposed plan. The beta spectrum, studied with the double focusing spectrometer, appears to be complex, having three components whose energies are 531, 447, and 405 kev, with relative intensities of 68%, 22%, and 10%, and logft of 6.7, 6.9, and 7.2, respectively. GADOLINIUM-161 formed by neutron capture in with a half-life of 7.15 days, certain other lines perGd160 decays with a 3.7 minute half-life to terbium- sisted with a longer half-life. These were recognized as 161. This activity in turn emits beta and gamma radia- due to gamma rays in europium, which must have been tion with a half-life found in the present investigation present as an impurity, even in the separated terbium. to be 7.15 days, terminating in dysprosium-161. A The relative intensities of the three L lines of the gamma transition of energy 49.0 kev had been reported' 25.6 kev and the 48.9-kev gamma rays are shown in for this activity. An additional gamma ray of energy Table II. These are compared with the calculated L approximately 75 kev and a beta upper energy of 550 shell coefficients of Rose et al.5 for a pure M1 transition kev were observed2 by the scintillation method. at this energy and for a sufficient admixture of E2 to be Coulomb excitation by alpha rays on unseparated in agreement with the observed data. The possibility dysprosium showed3 gamma rays with energies of 76 that the 25.6-kev gamma is an electric dipole transition and 166 kev, the latter probably not being in Dy161. is not completely excluded. The L2 line of the 57.3 A proportional counter study of low-energy photons indicated a 26-kev transition.4 TABLE I. Conversion electron energies in Dy'61 and their interpretation. (Numbers italicized in column 4 indicate arbitrary With the stronger sources now available a rein- normalization for each group of lines.) vestigation of the activity seemed desirable. A specimen of separated Gd160, enriched up to 95.4 percent, Electron Energy Gamma was irradiated for a week in the maximum flux of the energy Assign sm, Relative energy heavy water Argonne reactor. Beta energies were 16.4 L, 25.5 10.0 studied with the double focusing magnetic spectrometer, 17.0 L2 25.6 7.5 using a scotch tape backed source and 15 /ig/cm2 17.8 L3 25.6 6.3 Zapon window. Gamma energies were evaluated from 25.3 N 25.7 25.6 conversion electrons in magnetic spectrometers and coincidences observed with the scintillation spectrometer. 39.9 L, 49.0 10.0 40.3 L 48.9 1.6 Some twenty-five electron conversion lines were ob- 41.0 La 48.8 0.7 served and their energies measured as shown in column 46.9 M 48.9 1, Table I. The interpretation of these lines yields seven 48.6 N 49.0 48.9 gamma energies, four of which had not been previously 48.1 L, 57.2 10.0 reported. The relative intensities of many of the lines 48.6 L2 57.2 49.4 L, 57.2 2.5 were measured with the microphotometer and the 55.6 M 57.6 relative values for each group shown in column 4. The 57.1 N 57.5 57.3 clearly resolved 18.6-kev electron line was interpreted 20.8 K 74.6 10.0 as an L1 line for a gamma ray of 27.7 kev. Had this 65.8 L1 74.9 5.5 been a K line then an L, at 63.3 kev should have been 66.9 L3 74.7 2.2 73.0 M 75.0 expected, but it was not observed. In addition to the 74.5 N 74.9 74.8 group of electron lines tabulated, all of which decayed 24.4 K 78.2 t This work was supported jointly by the Office of Naval 69.2 L1 78.3 78.0 Research and the U. S. Atomic Energy Commission. 52.4 K 106.2 1 Cork, LeBlanc, Nester, and Stumpf, Phys. Rev. 88, 685 (1952). 97.3 106.4 106.2 2 R. Barloutaud and R. Bellini, Compt. rend. 241, 389 (1955). 97.3 L 106.4 106.2 3N. Heydenberg and G. Temmer, Phys. Rev. 100, 150 (1955). 4Scharff-Goldhaber, der Mateosian, McKeown, and Sunyar, Phys. Rev. 78,325(A) (1950). 6 Rose, Goertzel, and Swift (unpublished). 481

482 CORK, BRICE, SCHMID, AND HELMER TABLE II. Theoretical and observed relative L-shell intensities observed between (76, 50); (50, 25); and (50, 50) kev for the 25.6- and 48.9-kev gamma rays. for the 25.6- and 48.9-ke gamma rays. gammas. When lead shielding is used so as to minimize 25.6-key gamma 48.9-key gamma the effect of backscattered iodine x-rays (28 kev), there aLl:aL2:aL3 aL1:aL::aL3 still appeared to be a (25, 25) kev coincidence. These Pure M1 10:0.9:0.16 Pure M1 10:0.8:0.2 data are in accord with the arrangement shown. Ml+E2(2%) 10:6.0:8.5 M1+E2 (%) 10:1.1:0.6 The Kurie plot of the beta spectrum was found to be Observed 10:7.5:6.3 Observed 10:1.6:0.7 complex. Since all gamma rays observed were of low energy, it was expected that the maximum energies of gamma falls together with the N line of the 48.9-kev all beta components would lie rather close together. gamma ray so that its intensity and hence the multi- In order to avoid the large uncertainties resulting from polarity of the transition cannot be expressed with certainty, although the possibility of electric quadrupole is eliminated. The K/L ratio for the 74.8-kev gamma is compatible with an E2 transition. The multipolarities of the other weaker gamma rays were not determined. A A nuclear level scheme as shown in Fig. 1 satisfies both the observed energies and the relative intensities B'. of the gamma rays. In this plan the 25.6-kev gamma ray should be the strongest. Actually its L lines photographically appear weaker than the L lines for the 48.9kev gamma, but when the proper correction for the C variation of emulsion sensitivity with energy is made, the expected relationship appears reasonable. To check the proposed level scheme coincidence measurements were made with a scintillation spectrometer. The fine resolution obtainable with the magnetic spectrometers could of course not be obtained with the scintillation device. The singles gamma-ray spectrum is found to consist of three broad peaks at 25, 50, and 76 kev, each 200 300 400 of which is believed to be composite. Coincidences were ENERGY, KEV 65Tb'696 a7.15 d FIG. 2. Analysis of the Kurie plot of the beta spectrum of Tb'61. The set of points A represents the composite spectrum. The lines B, C, and D indicate the separate Kurie plots of the three components whose energies are 531, 447, and 405 kev. The points adjacent to C and D indicate the result of previous subtractions. determining each component by only a few points near 405 its upper limit, the set of experimental points was fitted \ 447 \ as the sum of a number of components, assumed to be 166 of allowed form, an assumption subsequently justified 66D \7 9\, by the logft values. It was found that two components 531 \ 132.0 were not sufficient but the data above 200 kev could be 27.7 573 fitted well by three components, as shown in Table III \\103_ 9 and Fig. 2. Deviations below 200 kev are probably due, at least in part, to backscattering in the source. 06.2 The spin of the ground level in Dyl'6 has been ob\_, 74.8 served and reported to be probably 7/2 in one report6 and 5/2 in the other.7 Odd parity is predicted by the \ 78.3 shell model. Similarly the ground level in Tb'61 is pre48.9 7 48 dicted to have even parity but the spin may have values 3/2, 5/2, or 7/2. This isotope lies in a region where - 25.6 rotational bands are to be expected. However, the levels at 25.6 and 74.8 kev cannot be the first two excited 25.6 levels of a rotational band with a ground state spin 6 K. Murakawa and T. Kamei, Phys. Rev. 92, 325 (1953). FIGo. 1. Proposed nuclear energy level scheme for Dy161. The 7 A. H. Cooke and J. G. Park, Proc. Phys. Soc. (London) heavy lines indicate the strongest transitions. A435, 282 (1956).

NUCLEAR LEVELS IN Dyl'6 483 greater than ~. If the ground state spin is assumed to be TABLE III. The resolution of the beta spectrum of Tb'61. ~, then these two excited levels can be used to calculate a decoupling parameter a= -0.071, and the next Maximum Percent energy, key abundance Log ft AI, parity rotational level is predicted at 134.5 kev. The vibrationrotation interaction correction, which is proportional 531-10 68% 6.7 0 or 1, yes to 12(1+1)2, for this 7/2 level amounts to about -2 447-10 22% 67.29 0 or 1, yes kev, bringing the energy of the expected level into good agreement with the one observed at 132 kev. This apparent sequence of rotational levels seems to be observed ground state spin, Coulomb excitation fortuitous, however, since it is not supported by the studies,' or character of the beta transitions.

VII DECAY SCHEME OF Ptg99

Reprinted from The Physical Review, Vol. 104, No. 6, 1670-1673, December 15, 1956 Decay Scheme of Ptl99t J. M. LEBLANC, J. M. CORK,* AND S. B. BURSON Argonne National Laboratory, Lemont, Illinois (Received September 12, 1956) The radiations of the 30-min activity of Pti0 have been investigated with 1800 magnetic photographic spectrometers and a 10-channel coincidence scintillation spectrometer. This activity of platinum has been found to decay by the emission of four beta rays with maximum energies of 0.8, 1.1, 1.3, and 1.7 Mev. Gamma rays with energies of 0.074, 0.197, 0.246, 0.318, 0.475, 0.54, 0.71, 0.79, and 0.96 Mev were detected. Extensive beta-gamma and gamma-gamma coincidence measurements were made; and an energy level scheme is proposed which is consistent with the results of all of the experiments. A THIRTY-MINUTE activity which is produced terpreted as K internal conversion electron lines of by neutron capture in platinum was first reported gamma rays emitted in the decay of Pt'". in 1935.1,2 McMillan et al.3 assigned this activity to Pt'99. The photon spectra of the 30-min platinum activity In 1941, Krishman and Nahum4 studied the radiations was studied with a 10-channel coincidence scintillation emitted in the decay of Ptl'9 and established, by means spectrometer.6 of aluminum absorption experiments, that beta rays The NaI(TI) pulse-height distribution from the with a maximum energy of 1.8 Mev are emitted. gamnla-rays of a PtO source which was irradiated for Sources of Pt'99 were obtained in the present investi- about 15 minutes is shown as the top curve in Fig. 1. gation by neutron irradiation of normal PtO. Seven Because of the short irradiation times, the activities internal conversion electron lines were detected with of Au'99 and Ptl97 were not observed in these sources. 1800 spectrographs and are listed in Table I. The The various peaks in the distribution are interpreted as interpretation of these lines are listed in column 2 of indicating the presence of nine gamma rays with Table I, and the gamma-ray energies are listed in energies of 0.074, 0.197, 0.246, 0.318, 0.475, 0.540, 0.715, columns 3, 4, and 5. The lines at 124, 144, 155, and 0.790, and 0.96 Mev. All of these peaks were observed 1_90 kev are identified by their energies as internal con- to decay with a half-life of 30 3 min and are, therefore, version electron lines in Hg, due to gamma rays emitted assigned to Pt'99. in the decay of Au'99, the daughter product of Pt'99. The peak at about 70 kev in the pulse-height distribuThe 268- and 332-kev electron lines have the K- L tion occurs at an energy rather close to that of the K energy difference of Pt and are assigned to the 80-min x-rays of gold (67 kev). One might conclude that it is activity of Ptl97m which has been reported5 to decay due entirely to the gold x-rays. The energy of the peak by the emission of a 337-kev gamma ray. The energy is, however, slightly higher than the x-ray energy. In of this transition as determined in the present study is order to determine if this is an energy shift due to the 346 kev. The remaining three electron lines are in- presence of a gamma ray of about this energy, the scintillation spectrometer was set so that the ten TABLE I. Energies and interpretations of the observed channels just covered this peak. Then, without changing internal conversion electron lines. the spectrometer, the pulse-height distributions due to T1 x-rays (71 kev), the Pt'99 peak, and the Pt'99 peak in Electron line Gamma-ray energies coincidence with the 246-kev gamma rays, were reenergy in kev Interpretation Pt Au Hg 116 Au K 197 TABLE II. Gamma-gamma coincidences observed in Ptln. 124 Hg K 208 Where coincidences were observed between two gamma rays, 144 Hg L 159 an X is placed at the intersection of the corresponding row and 155 Hg M 159 column. The symbol 0'is used for gamma rays which are not in 165 Au K 246 coincidence and blank spaces indicate cases where no data are 190 Hg L 208 available. 235 Au K 316 268 Pt K 346 332 Pt L 346 Gamma rays Gamma rays (energies in kev) (energies in kev) 960 790 715 530 475 318 246 197 74 tWork performed under the auspices of the U. S. Atomic 74 o X X X ~ X X Energy Commission. 197 x X X X X 246 0 X 0 0 X X * University of Michigan, Ann Arbor, Michigan. 318 0 0 0 X 0 0 X 0'Amaldi, D'Agostino, Fermi, Pontecorvo, Rasetti, and Segre, 4750 0 0 0 X X X X Proc. Roy. Soc. (London) A149, 522 (1935). 715 O o X 2 McLennan, Grimmett, and Read, Nature 135, 147 (1935). 790 0 0 0 0 8 McMillan, Kamen, and Ruben, Phys. Rev.52, 375 (1937). 960'4 R. S. Krishman and E. A. Nahum, Proc. Cambridge Phil. Soc. 37, 422 (1941).' N. Hole, Arkiv.Mat. Astron. Fysik 36A, No. 9 (1948).' S. B. Burson and W. C.Jordan, Phys. Rev. 91, 498 (1953).

IO0 0.07 0.197 NORMAL SPECTRUM _e' l — |- G 11COINCIDENCE WITH BETA RADIATION o I0 ~ 0.318 I: r \ 0.2461 0.540 1 A_ I0.475 I rI J IX LU I WQ: I I I Z I- FIG. 1. The Na pls- Ip I u lse height distribution of the t gamma rays of 78Pt1be (30 c I main)..S W A 0.79 w I x 0ct~~~~~~~ o.96 10 0.x\ BACKGROUND DUE / \ TO No IMPURITY 0 0.2 0.4 0.6 0.8 1.0 1.2 ENERGY (Mev) corded. The results are illustrated in Fig. 2. It can be half-life which is comparable to the resolving time of seen that the Pt"99 peak in the normal distribution the coincidence circuit, i.e., about 2 usec. occurs at almost exactly the same energy as the T1 By using an anthracene crystal for a beta-ray dex-ray. This energy is 3 key too high for the peak to be tector and measuring the attenuation in Al of the beta due entirely to Au x-rays. The fact that the Ptr9" 70-kev rays which are in coincidence with the various gamma peak is complex is clearly illustrated by the coincidence rays, it was established that the 0.197- and 0.54-Mev distribution (the dashed curve). The structure of this gamma rays follow a beta ray which has a maximum peak indicates the presence of a gamma ray at 74 kev. energy of 1.14-0.1 Mev. Similarly, it was established In addition, the small hump on the low-energy side of that the 0.246- and 0.318-Mev gamma rays follow a this peak occurs at about the energy of the Au x-ray. 1.3~0.1-Mev beta my, and the 0.71-, 0.79-, and 0.96Thus, one concludes that a 74-kev gamma ray is Mev gamma rays follow an 0.8d0.1-Mev beta ray. emitted in the decay of Pt"'9, and that the 70-kev peak A beta ray with a maximum energy of about 1.74-0.2in the normal distribution is a combination of this Mev was detected in the singles aluminum absorption gamrha ray and Au x-rays. experiment, but was not observed to be in coincidence The pulse-height distribution of the gamma rays with any gamma rays. It is interpreted as a beta transiwhich are in coincidence with beta rays was measured tion to the ground state of Au"'. and is shown as the dashed curve in Fig. 1. The 0.48, Extensive gamma-gamma coincidence measurements 0.71,0.79, and 0.96 Mev gamma rays are not so strongly were made, and the results are summarized in Table II. in coincidence with the beta rays as the other gamma The gamma rays are listed in the first row and column. rays. One explanation of this would be that these four Where coincidences are observed between two gamma gamma rays are transitions from a level which has a rays, an X is placed at the intersection of the appro

. \Pt1 Ln COINCIDENCE 0.54 0.54 0.54 e / ITH 246kev GAMMA I /: a: \ z I S S SNLSi//\\ COINC..WITH 0 0/ _ _ _No W VOLTS a a / \\(a) (b) (c) /1 FIG. 4. Gamma-gamma coincidences in the uz~~~~~~~ 1 /~~~ \,~ ~0.48- to 0.54-Mev region. 0 o TAe X-RAY I 197-kev gamma ray. One striking feature of the coincidence distribution is the intensity of the 246-kev peak 6o0 8'0 relative to the intensity of the 197-kev peak. If one ENERGY (kev) assumes that a small portion of the 246-kev coincidence Fro. 2. NaI pulse-height distributions of the 70-kev peak. peak is due to coincidences with x-rays, then one can conclude that the 74-kev transition is in coincidence priate row and column. Gamma rays which are not in with approximately equal amounts of the 197-kev and coincidence are indicated by an 0, and the spaces are the 246-kev gamma rays. Since the 197-kev photopeak blank where no data are available. in the normal distribution is considerably stronger than Strong coincidences were observed between the 74- the 246-kev photopeak, the 197-kev transition must be kev transition and several other gamma rays. The NaI in coincidence with more than just the 74-kev and the pulse-height distribution of the gamma rays which are 246-kev transitions. in coincidence with the 74-kev transition is shown as If one examines the pulse-height distribution of the dashed curve in Fig. 3. From this distribution, one gamma rays which are in coincidence with the 197-kev can conclude that the 74-kev transition is in coincidence photopeak, one finds that it is in coincidence with the with 197-, 246-, 475-, and 715-kev gamma rays, and not in coincidence with the 318-, 540-, and 790-kev Pt'9 gamma rays. The small coincidence peaks at 318- and (30min) 540-kev are interpreted as due to coincidences With the x-rays resulting from the internal conversion of the 1.3 which areinoi v 2-2X IO'G eC I 715 475 790 t3 it I540 -960 o.5 03 0.3 0.4 0.5 O O. 6 o. 0.. 7. -4 FIG. 3. The NaI pulse-height distribution of the gamma rays 197 which are in coincidence with the 74-key transition. Solid curve is the normal pulse-height distribution and the dashed curve is the coincidence distribution. Fio. 5. The proposed decay schem.e of..Ptm.=

246-, 318-, 475-, and 540-kev transitions. The counting clude that the 475-kev gamma ray is in coincidence rates were not high enough to determine if the gamma with both the 246- and 318-kev transitions, and that rays with energies above 700 kev are also in coincidence the 540-kev gamma ray is not in coincidence with the with this transition. 246-, 318- or the 475-kev transitions. In a similar The 0.48-0.54 Mev region of the pulse-height distri- manner, it was established that the 246- and 318-kev bution is shown in Fig. 4. The normal pulse-height radiations are not in coincidence with one another. distribution is plotted in each part of the figure as a The proposed decay scheme for Pt'" is shown in solid curve, and the distributions from gamma rays Fig. 5. This scheme includes all of the beta rays and which are in coincidence with the 246-, 318-, and 475- gamma rays which were detected in this study. The kev photopeaks are plotted as dashed curves in (a), (b), arrangement of the transitions is consistent with all of and (c), respectively. From these curves one can con- the coincidence measurements.

UNIVERSITY OF MICHIGAN 41111 01111 24 311259111111111111411I 3 9015 02845 3259