ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR PROGRESS REPORT TO JANUARY 1, 1955 INVESTIGATION OF NUCLEAR-ENERGY LEVELS J. M. CORK PrOfessor of Physics Project M670-2 OFFICE OF NAVAL RESEARCH, U. S. NAVY DEPARTMENT CONTRACT N5ori-116, PROJECT ORDER III, ONR PROJECT NRI)24-01

tilL LkM a j9 Ir S

FOREWORD This group of reprints of papers published in the Physical Review during the year is submitted as a progress report for the year 1954. 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 CONTENTS Paper No. DECAY OF 66DY165m (1.2 min) AND 66Dy165 (2.3 hr). Phys. Rev. 92, 1218 (1953). Jordan, Cork, and Burson. I THE GAMMA SPECTRA OF Cd117 AND In117. Phys. Rev. 93, 916 (1954). LeBlanc, Cork, and Burson. (Abstract) II RADIATION FROM ANTIMONY 122. Phys. Rev. 93, 1059 (1954). Cork, Brice, Hickman, and Schmid. III DECAY OF V52. Pkys. Rev. 93, 1124 (1954). LeBlanc, Cork, Burson, and Jordan. IV NEUTRON CAPTURE IN THE SEPARATED ISOTOPES OF PLATINUM. Phys. Rev. 94, 1218 (1954). Cork, Brice, Schmid, Hickman, and Nine. V THE ACTIVITIES OF Zn71. Phys. Rev. 94, 1436 (1954). LeBlanc, Cork, and Burson. (Abstract) VI THE DECAY OF Pt199. Phys. Rev. 95, 627 (1954). LeBlanc, Cork, and Burson. (Abstract) VII ENERGIES OF THE RADIATIONS FROM Ce144 AND Pr144. Phys. Rev. 96, 1295 (1954). Cork, Brice, and Schmid. VIII iv

I DECAY OF 66DyL65m (1.2 min) AND 66Dy 65 (2.3 hr)

Reprinted from THE PHYSICAL REVIEW, Vol. 92, No. 5, 1218-1221, December 1, 1953 Printed in U. S. A. Decay of 66Dyl65m(1.2 min) and 66Dy165(2.3 hr) W. C. JORDAN, J. M. CORK, AND S. B. BURSON Argonne National Laboratory, Lemont, Illinois and University of Michigan, Ann Arbor, Michigan (Received August 24, 1953) The activities induced by neutron capture in Dy164 have been studied with 1800 photographic internal conversion electron spectrometers and a scintillation coincidence spectrometer. The metastable transition energy is 108.0:=0.2 kev. Other gamma rays of approximately 160, 360, and 515 kev are associated with the 1.2-min activity and appear to follow beta decay from the metastable level. Gamma rays of 94.44-0.2, 279.4+-0.8, 361.24-1.0, 63443, 7104-20, and 10204-30 kev follow the 2.3-hr beta decay from the ground state. Coincidences are observed between members of the pairs (279)-(710) and (361)-(634). The 94-kev gamma ray is coincident with a beta transition of about 1.2 Mev, while the other gamma radiations are coincident with a softer beta component (-0.3 Mev). INTRODUCTION propose a reasonable level scheme. Another measureIN 1935, Marsh and Sugden' and, independently, ment of the gamma-ray energies has been made by Hevesy and Levi2 reported that a very strong beta Miller and Curtiss,1 who report energy values of 0.37 activity was produced when Dy was exposed to neu- and 1.0 Mev. Clark9 has set an upper limit of 1.1 Mev trons from a Ra-Be source. They found the half-life for the gamma energy and has also detected betato be about 2.5 hr. A recently reported value is 2.310 gamma and gamma-gamma coincidences. ~t0.002 hr.3 Several measurements of the beta energy A short-lived Dy activity with a half-life of 1.25 min using cloud chamber and absorption techniques have was first reported by Flammersfeld.l2 Electrons with an been made.2'4-8 The values reported from these investiga- energy of approximately 130 kev were detected. These tions range from 1.1 to 1.9 Mev. Two spectrometer were interpreted as arising from internal conversion of measurements have listed the maximum beta energy an isomeric transition in Dy'63. Later work by Inghram as 1.18 Mev9 and 1.24 Mev.10 In addition to the 1.24- et l.3 has established that this, as well as the 2.3-hr Mev beta ray, Stis0 has resolved two lower-energy activity, is associated with Dy'65. The cross sections for Mev beta ray, Slaitis1~ has resolved two lower-energy production of the 1.25-min and 2.3-hr activities were components of 0.42 and 0.88 Mev. Meitner6 reported observed to be approximately equal, indicating that gamma radiation with an average energy of about 0.6 only the metastable state is formed directly in the Mev to be associated with this Dy activity. From a capture process. Since growth of the 2.3-hr activity had study of the internal conversion electron spectrum and not been observed,12 it was suggested that a small perthe spectrum of electrons from secondary radiators, centage of the decay o f the metastable state was by Slatis10 concluded that gamma transitions of 0.91, 0.36, emission of a beta particle. In the present research some and 0.76 Mev were present. With the postulation of one additional evidence for the existence of such a transition additional unresolved beta component, he was able to has been found. The conversion electron spectrum of this activity has 1 J. Marsh and S. Sugden, Nature 136, 102 (1935). 2 G. Hevesy and H. Levi, Nature 136, 103 (1935). been investigated with spectrometers by Holel4 and 3 Sher, Kouts, and Downes, Phys. Rev. 87, 523 (1952). Caldwell.l5 The former noted that conversion was pre4 R. Naidu and R. Siday, Proc. Phys. Soc. (London) 48, 332 (1936). 5 Gaerttner, Turin, and Crane, Phys. Rev. 49, 793 (1936). " L. Miller and L. Curtiss, Phys. Rev. 70, 983 (1946). 8 L. Meitner, Arkiv Mat. Astron. Fysik A27, No. 17 (1940). 12A. Flammersfeld, Naturwiss. 32, 68 (1944); Z. Naturforsch. 7 S. Eklund, Arkiv Mat. Astron. Fysik A28, No. 3 (1941). 1, 190 (1946). 8 A. F. Clark, Phys. Rev. 61, 203, 242 (1942).'3Inghram, Hayden, and Hess, Phys. Rev. 71, 270 (1947); 9 B. Dzelepov and A. Konstantino, Compt. rend. acad. sci. Inghram, Shaw, Hess, and Hayden, Phys. Rev. 72, 515 (1947). (U.R.S.S.) 30, 701 (1941). l N. Hole, Arkiv. Mat. Astron. Fysik A36, No. 2 (1948). 10 H. Slitis, Arkiv Mat. Astron. Fysik A33, No. 17 (1949). 15 R. Caldwell, Phys. Rev. 78, 407 (1950).

1219 DECAY OF 66Dy165m(1.2 MIN) AND 66Dy165(2.3 HR) dominantly in the L shell and found the transition TABLE I. Internal conversion electrons associated with the 1.2-min Dy activity. energy to be 102 kev. The latter resolved five conversion lines and reported a value of 109.0 kev for the transition energy. By means of a scintillation spec- energy Relative Interpre- sum energy trometer, Kahnl6 found a value of 102 kev. Caldwell (ke) intensity to (ke) (ke) KL also investigated the conversion electron spectrum of the 54.2 3 K (Dy) 108.0 108.0+-0.2 0.154-0.05 2.3-hr activity in the region below 300 kev. He observed 99.4 10 L2 108.0 100.3 10 L3 108.1 several electron lines associated with conversion of an 106.3 5 M2, M3 108.1 87.8-kev gamma ray, and in addition, a single line at 107.8 1.5 N 108.1 461 K (Ho) 517 5174 —3 219 kev. The latter has been interpreted17 as the K line of a transition which could be fitted into the level scheme proposed by Slatis. As indicated in a preliminary of only two of the transitions. These measurements reports8 of the present study, energy values of the transi- were made with a Leeds and Northrup recording phototions involved and the results of coincidence experi- densitometer. After the data were replotted on a linear ments are inconsistent with this interpretation. scale and the background due to the beta distribution An accurate measurement of the low-energy gamma was subtracted, the area under a line profile was measray has been made by Mihelich and Church.19 They ured. This area, when corrected for variations due to found the energy to be 95.1 kev and the ratio of con- the geometry of the spectrometer and sensitivity of the version in the K and L shells to be 5.9. photographic emulsion, is taken as the relative intensity of the line. The geometry correction consists of simply multiplying each value by the corresponding radius of the electron path in the spectrometer. The emulsion K X-RAY sensitivity factor was determined according to the method described by Rutledge, Cork, and Burson.20 No 360 515 corrections are made for differential absorption of the at ~electrons in the source. Ir ESCAPE 1 60 RESULTS AND DISCUSSION o= 1.2 min Internal conversion electrons associated with the 1.200, 200VL 300 00 00 600 min metastable transition are easily detected. Five ENERGY,kev lines corresponding to a transition of 108.0 kev were FIG. 1. Gamma-ray pulse-height distribution of 66Dy165m(1.2 min). observed (Table I). The energy is in fair agreement with the value 109 kev reported by Caldwell. A careful EXPERIMENTAL PROCEDURE measurement of the separation of the two L-lines was made, and it was found that the energy difference is The apparatus of the present investigation consists of characteristic of conversion in the L2 and L3 sub-shells, eters20 and a scintillation coincidence spectrometer.21 as has been proposed by Mihelich.22 It is interesting to Sources were normal Dy oxide irradiated in the Sources were normal Dy oxide irradiated in the TABLE II. Internal conversion electrons associated with Argonne heavy water-moderated reactor. Several the 2.3-hr Dy activity. samples of Dysprosium oxide were used. One was known to be spectrographically pure except for 0.4-percent Electron Energy Transition holmium and 0.1-percent yttrium. energy Relative Interpre- sum energy (kev) intensity tation (kev) (key) K/L Eastman no-screen x-ray and NTB emulsions were 38.8 60 K (Ho) 94.4 94.4-0.2 7.7-2.0 used as detectors in the electron spectrometers. Film 85.0 7.8 L1 94.4 backings were used in survey work, but where density 92.2 -1.5 M 94.3 and accurate energy measurements were made, a glass 93.9 N 94.3 plate backing was employed. Photodensitometer meas- 223.8 K (Ho) 279.4 279.4+0.8 >5a urements of line intensities were practicable in the case 270.0 L1 279.4 305.8 K (Ho) 361.4 361.2+-1.0 >5a 16J. Kahn, Oak Ridge National Laboratory Report ORNL 351.7 K 361.1 1089, 1951 (unpublished). 7 M. Goldhaber and R. Hill, Revs. Modern Phys. 24, 179 578 K (Ho) 634 634+3 (1952). -623 L -632 18 Jordan, Cork, and Burson, Phys. Rev. 91, 497 (1953). 19 J. Mihelich and E. Church, Phys. Rev. 85, 690 (1952). 20 H. Keller and J. Cork, Phys. Rev. 84, 1079 (1951); Rutledge, a Visual estimate. Cork, and Burson, Phys. Rev. 86, 775 (1952). 26 S. Burson and W. Jordan, Phys. Rev. 91, 498 (1953). 22 J Mihelich, Phys. Rev. 87, 646 (1952).

JORDAN, CORK, AND BURSON 1220 sorbers between the source and the detector. Therefore, K X-RAYr.,,, I the 360-kevy peak is not due entirely to excitation of the _j crystal by Compton electrons of the 515-kev gamma ray. a>279 Coincidences between the 360- and 515-kev gamma z A II I\ I rays were not observed. Pulses in the region of the 36036I VI.~ \"~ 3kev peak were, however, observed to be coincident with 94 1 those of the 160-kev region. It is probable that the 160m i 11 1 V \ - and 360-kev transitions are in cascade and that the n 11 X50 | 515-kev one is the crossover. It might be assumed that these gamma transitions o IIIII1 1 634 l710 1 1 1020follow the 108-kev metastable transition. However,,,, Im_, \these radiations appear to be coincident with a beta 0 200 400 600 800 o000 1200 ENERGY, Rev ray and not with the radiations associated with the metastable transition. Beta decay of the metastable FIG. 2. Gamma-ray pulse-height distribution of 66Dy'65(2.3 hr). metastable transition Beta decay of the metastable state has not been detected previously, although the note that the M conversion also appears to be in the possibility of its existence has been suggested.13 AddiM2 and/or M3 sub-shell.' tional evidence of this beta transition was observed with the photographic spectrometers. The background The K/L conversion ratio is 0.15+0.05, a somewhat with the photographic pectrometers The background darkening of the emulsion, due to the continuous beta higher value than that obtained by Caldwell, but in darkening of the emulsion, due to the continuous beta good agreement with the Goldhaber and Sunyar23 distribution, empirical relation of Z2/E versus K/L for an electric for short periods immediately after irradiation of the octopole transition. source, as compared with a plate with an equivalent An investigation of the 1.2-min activity with the exposure to the 2.3-hr activity after the 1.2-min acscintillation spectrometer revealed the presence of tivity had decayed. An additional weak conversion line higher energy gamma radiations. Peaks in the pulse- was noted which may be associated with the short height distribution corresponding to gamma rays of activity. The energy of the electrons is 461 kev. These approximately 160, 360, and 515 kev are present in are probably K electrons for the -515-kev transition. addition to the K x-ray, its associated escape peak, and If so, a better value for the energy of this transition is the 108-kev peak (Fig. 1). All of these decay with the 517 kev, assuming the K binding energy of holmium is 1.2-min period. The ratio of the heights of the 360- to be used. and 515-kev peaks can be varied by placing lead ab- By comparing the heights of the 108-kev and x-ray CORRESPONDING TEN-CHANNEL SINGLE CHANNEL COINCIDENCE DISTRI BUTION 634 634 4 / //.\ // \\ _j FIG. 3. Coincidence a1 1 1 v M I 710 L- 200 710/ | butionscorrespondingto za: 1 1200 0 six window settings of 1 the single-channel specW io \/\ 100 A\\ trometer are shown. For ccI j.200 x 710 200 I I I comparison, the normal en I I [ I I \ I I < "spectrum is shown as a | {[279 |6t dashed curve in each 200 71t 200 710 I I 62 2 3 4 5 6of 66Dy'~(2.3 hr). / \ 200/ 710 6 750 butions corresponding to I 407the single-channe l specl x 0 trometer are Shown. For ENERGY, Nev 2 M Goldhaber and A. Sunyar, Phys. Rev. 83, 906 (195).curve in each 23 M. Goldhaber and A. Sunyar, Phys. Rev. 83, 906 (1951).

1221 DECAY OF 66Dy165m(1.2 MIN) AND 66Dy165(2.3 HR) peaks (Fig. 1), a rough estimate of the K conversion y16 H.65 coefficient of the 108-kev transition may be obtained. 67 Neglecting any contribution to the x-ray intensity from 13,2 1.2 min conversion of the higher energy gamma rays, this,o(E 3). r quantity may be estimated to be about four. Since 72\_.3\ conversion of this transition is only about 10 percent \"0.. _ in the K shell, the total conversion coefficient would be FIG. 4. Proposed decay about forty. scheme for 66Dyls5m(1.2 279 min) and 66Dyl65(2.3 hr). (The order of the 279- \ z 2 2.3 hr 710-kev cascade is arbi- \Mev 634kev trarily chosen.) \ \ \ oPkev Internal conversion electrons associated with the 2.3-hr activity are listed in Table II. The observed \\ 160kw -10kev conversion lines are interpreted as arising from four transitions of 94.4, 279, 361, and 634 kev. The measured 361 kev energy of the 94.4-kev transition is in fair agreement d5 94.4kev with the results of Mihelich and Church. They report 97/\ the energy to be 95.1 kev and the type of radiation as a mixture of M1 and E2. The present measurement of mentary experiment, in which the coincidence spectra the K/L ratio is in good agreement with the value pre- n e e e s in the region of the 279- and 361-kev peaks were obdicted for a pure M1 transition; however, the accuracy served as the single channel was scanned over the is too poor to rule out the possibility of the mixture. 634-710-kev region, yielded results in agreement with In the decay scheme of Goldhaber and Hi1,"8 this these transition is assumed to be in cascade with the 279-kev Coincidences between the other possible pairs of one, while the 361-kev is the crossover transition. This gamma rays were not detected. is not consistent with the present data. The discrepancy The results of beta-gamma coincidence experiments in the energy sum is well outside the limits of experi- transition is coincident with a indicate that the 94-kev transition is coincident with a mental error. beta ray of maximum energy approximately 1.2 Mev, An investigation of this activity with the scintillation while the other gamma radiations all appear to be spectrometer showed the presence of peaks in the pulsecoincident with a lower energy beta component of apheight distribution corresponding to the previously proximately 0.3 Mev. mentioned transitions, plus two others of approximately The proposed nuclear energy level scheme shown in 710 and 1020 kev (Fig. 2). Coincidence studies showed 710a tan 1020 key (Fg1. 2).aCoinci rdencem sde cashwe Fig. 4 is consistent with these data. It should be pointed thata the 279- and 70-key gamma rays form one cascade out that the transition of about 360 kev associated with pair and the 361- and 634-kev gamma rays are another. the 1.2-min activity has been assumed to be the same These conclusions are based on the results of two comas the more accurately measured 361-kev transition piementary experiments. plem nentar experiments, theten-channassociated with the 2.3-hr activity. Also, the order of In one experiment the ten-channel analyzer was In oe e t te t e analr ws the 279-710-kev cascade as shown in the figure is adjusted to cover the region of the 634- and 710-kev arbitrarily chosen peaks, while the single-channel spectrometer was varied The measured spin of the ground state of Ho16~ is in steps across the region of the 279- and 361-kev peaks. 24 7/2.24 On the basis of shell structure, orbital assignThe resulting coincidence distributions are shown in for the ground and first exments have been made 8 for the ground and first exFig. 3. The peak in the coincidence distribution is at cited states of both Dy. The results of cited states of both Dy165 and Ho105. The results of the 634-kev position when the single-channel side is this investigation are in agreement with these asaccepting pulses from the 361-kev transition, and at the signments 710-kev position when the single channel is accepting pulses from the 279-kev gamma ray. The comple- 24 H. Schiller and T. Schmidt, Naturwiss. 23, 69 (1935).

II THE GAMMA SPECTRA OF Cd117 AND In117

Reprinted from The Physical Review, Vol. 93, No. 4, 916, February 15, 1954 The Gamma Spectra of Cd74 and Ilnl. J. M. LEBLANC J. M. CORK,*. AND S. B. BURSON, Argonne National Labora. tory.-The.gamma spectra of Cd117 and In117 have been studied with 1800 photographic spectrometers and with a 10-channel coincidence scintillation spectrometer. Sources were obtained by irradiating enriched Cd116 in the Argonne heavy water reactor. Internal conversion electrons associated with 0.160-, 0.267-,-0.281-, and (.312-Mev gamma rays were observed. In addition to these, transitions of energy 0.43, 0.55, 0.72, 0;84, 1.27, 1.55, and 2.00 Mev were detected with the scintillation spectrometer. The decay of each peak has been followed. Chemical separations of the In from the Cd were made and the spectra of each fraction studied with the scintillation spectrometer. Then 0.160-, 0.312-, 0.55-, and 0.72-Mev gamma rays are associated with the In fraction, and all decay with a 2.3-hour half-life. The remaining gamma rays are in the Cd fraction. The 0.312-Mev gamma ray is the most strongly converted, and, furthermore, is not in coincidence with betarays. It is interpreted as an isomeric transition in Inl"'. Results of beta-gamma and gamma-gamma coincidence measurements will be discussed. * University of Michigan.

III RADIATION FROM ANTIMONY 122

Reprinted from THE PHYSICAL REVIEW, Vol. 93, No. 5, 1059-1061, March 1, 1954 Printed in U. S. A. Radiation from Antimony 122 J. M. CORK, M. K. BRICE, G. D. HICKMAN, AND L. C. SCHMID Department of Physics, University of Michigan, Ann Arbor, Michigan (Received November 30, 1953) Neutron capture in enriched Sb12L yields radioactive Sb'22 whose half-life is found to be 66.04-0.4 hr. In addition to the two previously observed gamma rays, present studies with scintillation and conversion electron spectrometers indicate the existence of six previously unreported gammas. The energies are 95,.553, 566, 616, 647, 694, 1100, 1200 kev with possibly something at 1.9 Mev. K/L intensity ratios for the conversion lines are observed only for the 553- and 566-kev gammas. The high-energy lines are observed only with the scintillation spectrometer. The beta spectrum is resolved into components with maximum energies at 2.004-0.03, 1.404-0.02, and 0.450 Mev, with.possibly some other lower energy present. Three gamma energies in Sb'24 are evaluated by their conversion electrons as 603.6, 644, and 727 kev. IN the early survey of radioactivities induced by slow does not exhibit the allowed shape. When the same neutron capture, Fermi et al. found1 a beta-emitting correction factor as used above is applied, an upper product in antimony, whose half-life was 2.5 days and energy limit of 1.4040.02 Mev is found, Subtraction whose beta energy, as determined by absorption in of this component gives a residual curve of maximum aluminum, was about 1.6 Mev. Subsequent studies energy 450 kev (curve C). However, this energy value have shown2 that this activity is undoubtedly in Sb22 is influenced appreciably by the type of correction -factor being formed from Sb121 whose natural abundance is: applied to curve B. The possibility of'lower energy 57.2 percent. More recently several reports on the beta components is not excluded. The relative abundenergies of the beta and the gamma radiations have ance of the three beta rays expressed in the order of appeared. These exhibit considerable variation in the decreasing energy is 36, 56, and 8 percent. The correvalue of the beta energies. In only one report is more sponding log ft values in the same order are 8.5, 7.7, than a single gamma ray mentioned. These results are and 6.7, respectively. summarized in Table I. In the: present investigation, antimony enriched in:. GAMMA ENERGIES mass 121 up to about 99 percent Was irradiated in the In the magnetic photographic spectrometers strong Argonne heavy-water pile. The gamma radiations were K and L electron lines appear with energies of. 534.2 studied both with photographic magnetic and scintil- which, if in tellurium, yield a gamma ray and 560.6 kev which, if in tellurium, yield a gamma ray lation crystal spectrometers. The beta radiation has at 566.0 kev. The K to L intensity ratio for the two. been analyzed by the large double-focusing magnetic lines is found to be7.0+1.5.'Weaker K and L lines are spectrometer provided with a thin window counter. observed for a gamma'ray of energy 553 kev, with a The half-life was determined from observation of the K/L value of approximately unity. Several additional decay through several octaves by the use of an ioniza- single electron lines are found and interpreted as K tion electrometer. lines in tellurium for gamma rays, following K capture BETA ENERGIES in Sb'22. All observed lines died with the same half-life The beaspcrm sfun o ecmpewhich was found to be 66.0i0.4 hr.'The energies' of Thebeta spectrum isfound to be o e consisting these electron lines'are 63.4, 584, 615, and 662 key, of at least three components. The composite Kurie plot yielding gamma rays with energies of 95.2, 616,647, is shown in curve A-, Fig. 1. The curve- shap-e at the and 694 kev. The weakest line is that corresponding to upper limit suggests a unique first forbidden transition with AI equal to 2 and a change in parity. It is found TABLE I. Previous data relative to Sb"Z. that the high-energy part of the Kurie plot can be corrected to a straight line by means of the Energy in Mev unique first-forbidden, tensor-type, correction factor Author 2 7. Cr'(Wo-W)2Lo+9Ll, where the factors Lo and L1 are MCa 1.36 1.94 RWb 0.57 obtained from the tables of Rose et al.3 A least squares KW 0568 fit to the corrected Kurie plot gives an upper energy- Cd'' 0.568 limit of 2.004-0.03 Mev. The remainder after subtrac- Me 1.19 1.77 Mf 1.46 tion of this component is shown in Curve B. This GCg 31s (No values) 0.56 0.680 residual curve is still complex, and its high-energy part 1Amaldi, DAgostino, Fermi, Po ntecorvo, Rasetti, and Segr, a L. Miller and L. Curtiss, Phys. Rev. 70, 983 (1946). Amasld, iAigostino, Fermi, Pontecorvo, xasetti, ~and egre', b W. Rall and R. Wilkinson, Phys. Rev. 71, 321 (1947). Proc. Roy. Soc. (London) A149, 522 (1935). c Kern, Zaffarano, and Mitchell, Phys. Rev. 73, 1142 (1948). 2 Mitchell, Langer, and McDaniel, Phys. Rev. 57, 1107 (1940). d c. Cook and L. Langer, Phys. Rev. 73, 1149 (1948);' Rose, Perry, and Dismuke, Oak Ridge National Laboratory Macklin, Lidofsky and Wuerb, Phys. Rev. 82,7334 (195148). Report, No. 1459, 1953. - g M. Glaubman and F. Metzger, Phys. Rev. 87, 203 (1952). 1059

1060 CORK, BRICE, HICKMAN, AND SCHMID 8_ 1.68 Mev with possibly something at 1.2 Mev and also at a higher energy such as 1.9 Mev, as shown by the singles curve A, in Fig. 2. After a decay of 7 days this trace has dropped to give the relative intensities shown in curve B, thus indicating that the 1.68-Mev gamma ray is in Sb'24 with its longer half-life, while the 1.10-Mev gamma and possibly the 1.2- and 1.9-Mev transitions 6 _- \ tj are in Sb'22. In the low-energy region, peaks are observed only for the gamma rays of energy 694, 566, and 27 kev. The last is due undoubtedly to the K x-rays of tellurium 5s_ following K capture in antimony. The energy is evaluated by comparison with the known peaks due to Cs'37 and Co60. For the very strong 566-kev radiation 4_- both Compton electron and escape peaks are observed as shown. COINCIDENCE STUDIES A 3-. By placing the radioactive source between two scintillation crystals each with its own output circuit, coincidence events could be observed. For gamma2_ \ B s \ gamma coincidences both crystals were made of NaI, thallium activated. For beta radiations a crystal of anthracene was employed. The window of one pulseheight analyzer could be adjusted to respond to gamma rays lying between definite energy limits and the other instrument could be swept through all of the gamma peaks in turn. In beta-ray studies the anthracene with''' its very thin window actuated one of the recording o.2 4.6.8 1.0 1.2 1.4 1.6 18 2.0 circuits. By interposing successive layers of aluminum E ( ME V) between source and crystal the counting rate was reduced so as to obtain a Feather curve. Either the FiG. 1. Resolution of the beta radiation from Sb.'2 thickness required to reduce the intensity to half-value, or the thickness required to reduce to the gamma the gamma ray at 647 kev. A lead radiator giving background, may be used empirically to give the beta photoelectrons showed K and L lines only for the strong upper energy limit. 566-key gamma ray. In Fig. 2 is also shown a coincidence curve C, when To insure that none of the observed electron lines one channel is set to respond only to the 566-kev could be attributed to Sb'24, which has been previously one channel is set to respond only to the 566-ke intensively studied,4 spectrometric exposures were made radiation and the other channel is varied to respond to intensively studied,4 spectrometric exposures were made of a strongly irradiated source of Sb123. The strongest successive gamma rays The 566-kev radiation is thus electron line is found to have an energy of 571.8 kev. seen to be in sequence with the 694-kev gamma. No This is a K line and it is accompanied by an L line of evidence could be obtained for the gamma-gamma about one-tenth its intensity, at 598.6 kev, so that the coincidences except for the tellurium x-ray at 27 kev. energy of the gamma ray is 603.6 kev. Weaker conversion electron lines are observed for gamma rays of energies 644 and 727 kev. Even the very strongest line,178 ESA C137 at 571.8 kev is not observable on the spectrograms 6 \ CA62 l 0 obtained with Sb'22, hence it seems quite certain that 7 17 none of the gamma rays attributed to Sb122 could be 300 due to Sb124 c'S- / AY Studies have also been made of the activity with a / 324COMPTON 1.10 scintillation crystal spectrometer. Due to the increased 010 \ 69/X \, sensitivity of this method, some slight response is,00 o, / 6.... \, \ obtained for radiation due to Sb24, particularly at high A \', \ energies. Peaks are obtained for gamma rays at 1.09 and -\' \ 100 200 300 400 500 600 700 B 1.0 L2 1.4 6 1.8 2.0 4'Langer, Lazar, and Moffat, Phys. Rev. 91, 338 (1953); Tomlinson, Ridgeway, and Gohalakrishnan, Phys. Rev. 91, 484 FIG. 2. Energy distribution with the (1953). scintillation spectrometer.

RADIATION FROM Sb 12 2 1061 The beta activity as a function of the thickness of aluminum is shown in curve A, Fig. 3. The thickness required to reduce the activity to that of the gamma background cannot be sharply determined but it is approximately 0.9 g/cm2 corresponding to an energy of SB'22 about 1.9 Mev. By recording only coincidences between beta response and the 566-kev gamma ray as the absorber is varied in thickness, curve B is obtained. The cut-off thickness is now 0.6 g/cm2 indicating an FEATHER CURVES energy of 1.4 Mev. This indicates that the 566-kev gamma transition follows in sequence the 1.4-Mev beta decay. Attempts to observe other beta-gamma c coincidences were not successful. The ground level of the even-even 52Te122 nucleus is undoubtedly a state of zero spin and even parity. If \.oMEV the uniquely forbidden 2.00-Mev beta transition goes directly to the ground state, then the 66-hour 51Sb'2 level is identified as having a spin of two and odd parity. There exists also in Sb122 a 3.5-minute isomeric state which has been reported5 to decay by a 69-kev gamma to the more stable level. The Z2/W value for the 566-kev.4 ME radiation is 4.8. In this region a K/L ratio of approximately 7 cannot uniquely determine the type of radiation, and on this basis alone it might be an E2 or any type of magnetic transition. The observation of coincidences with beta rays requires a short lifetime which would exclude all magnetic transitions except idro 300 560 700 960 1100 1300 M1, and possibly M2. For even-even nuclei the first ABSORBER(AL) MG/CM2 excited state is usually a level with s~pin two and even FIG. 3. Absorption of beta radiation observed with parity, which allows an E2 transition to the ground scintillation spectrometer. state. The nature of none of the other gamma transitions can be resolved. The low K/L ratio for the 553-kev of others. For example, 566 plus 553, 566 plus 694, gamma ray suggests a high-order multipolarity for the and 95 plus 553 will yield 1119, 1260, and 648, respectransition, such as E4 or M4. A long lifetime should tively, all of which are observed. No trace of positrons then be expected which may account for the absence of could be observed but there might conceivably be K additional coincidences. capture leading to Sn'22. In this event some of the It is possible to arrange a level scheme that will gamma rays might occur in tin. Level schemes that accommodate most of the observed data. Cross-over appear reasonable seem to require an additional lowtransitions can be identified from the fact that certain energy beta ray which is beyond the resolution of the gamma energies have values approximating the sums present work. This investigation received the joint support of the 5 E. derMateosian and M. Goldhaber, Phys. Rev. 82, 115 5E. derMateosian and M. Goidhaber, Phys. Rev. 82, 1 U. S. Office of Naval Research and the U. S. Atomic (1951); J. H. Kahn, Oak Ridge National Laboratory Report, U Office of Naval Research an d the U. S No. 1089, November, 1951. Energy Commission.

IV DECAY OF V52

Reprinted from THE PHYSICAL REVIEW, Vol. 93, No. 5, 1124-1125, March 1, 1954 Printed in U. S. A. Decay of V52 J. M. LEBLANC, J. M. CORK,* S. B. BURSON, AND W. C. JORDAN Argonne National Laboratory, Lemont, Illinois (Received January 14, 1954) T HE irradiation of normal V with thermal neutrons has been shown in Fig. 1. It is clear that there is only one gamma ray reported to produce three activities' which have been as- present to any appreciable extent in this activity. Its energy is signed to V52. These activities were found to decay with half-lives 1.444-0.02 Mev, and its half-life is 3.75 min. The:6 rays were of 2.6 min, 3.75 min, and 16 hr. Recent work has been reported2 on studied by absorption in Al, and it was found that a 3 ray whose the 16-hr activity and an energy level scheme proposed which maximum energy is about 2.6 Mev is in coincidence with the 1.44includes all three activities. Mev gamma ray. The coincidence Al absorption curve did not The present study of V52 was made using 180~ magnetic photo- differ from-the singles absorption curve, so that it is concluded that graphic spectrometers and a 10-channel coincidence scintillation most, if not all, of the beta rays feed the 1.44-Mev level in Cr52. spectrometer. Sources were obtained by neutron irradiation of An attempt was made to detect the 2.6-min activity reported by V2Os in the Argonne heavy water reactor. Renard. Sources were irradiated for periods of 1, 3, and 10 minutes Irradiations of about 5 minutes produce a strong 3.75-min and their decay followed with an ionization chamber and a viactivity in V. The conversion electron spectrum of such samples brating reed electrometer. The decay curves were all simple, with a was examined in the region of 10 kev to 2 Mev, and no electron half-life of about 3.7 min. Other investigators3 also find no evidence lines were detected. The scintillation spectrometer was used to for the metastable state in V52 reported by Renard. The assignment study the unconverted photons, and the resulting spectrum is of a 2.6-min activity to V is thus considered to be doubtful. A weak activity with a half-life of about 15 hr was found in V samples irradiated for about 15 hr. The scintillation spectrum of this activity, however, corresponds to the spectrum obtained from 0oo PHOTO PEAK the 15-hr Na24. A spectroscopic analysis of the V205 established that Na was an impurity with 0.05 percent abundance. In order to'700 _ | determine if any of the activity was due to V, the Na was chemically separated from the V after irradiation. Both the Na and the V 600~ -Pb X-RAY II |fractions were then counted with the scintillation spectrometer. It was found that the activity of the Na fraction was more than 100 ~0 times that of the V fraction, and that the V fraction was only two o it BACKSCATTERED Z 8 times the background. o 1 I 400- COMPTON The results of this study indicate that V52 decays with a 3.75-min half-life by the emission of a single beta ray of energy 2.6 Mev followed by a gamma ray of energy 1.44 Mev. Neither the 2.6-min 300 ~_ 300 _s4\ \nor the 16-hr activity previously reported in V52 was found. The authors wish to thank P. R. Fields, R. F. Barnes, and J. K. 200 Brody of the Argonne National Laboratory for kindly making the chemical separation and spectroscopic analysis. * University of Michigan, Ann Arbor, Michigan. v E. Amaldi et al., Proc. Roy. Soc. (London) A149, 522 (1935); G. A. Renard, Ann. phys. 5, 385 (1950); Cork, Keller, and Stoddard, Phys. Rev. 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 76, 575 (1949); L. A. Turner, Phys. Rev. 58, 679 (1940). ENERGY MEV 2 T. Wiedling, Phys. Rev. 91, 767 (1953). 3 J. E. Schwager and L. A. Cox, Phys. Rev. 92, 102 (1953); G. A. FIG. 1. Gamma-ray pulse-height distribution resulting from V52 (3.7 min). Bartholomew and B. B. Kinsey, Phys. Rev. 89, 386 (1953).

V NEUTRON CAPTURE IN THE SEPARATED ISOTOPES OF PLATINUM

Reprinted from THE PHYSICAL REVIEW, Vol. 94, No. 5, 1218-1221, June 1, 1954 Printed in U. S. A. Neutron Capture in the Separated Isotopes of Platinum* J. M. CORK, M. K. BRICE, L. C. SCHMID, G. D. HICKMAN, AND H. NINE Department of Physics, University of Michigan, Ann Arbor, Michigan (Received Februrary 23, 1954) Using the separated isotopes of platinum, irradiated in the pile, the energies of the gamma rays for the activities of Pti91, Pti93, and Pt195 have been evaluated. For Pt9i' fifteen gamma rays are found which fit well a simple level scheme. Pti93 emits isomerically a gamma ray followed by K capture to iridium, with the possible emission of a high-energy gamma. Pti95 emits a highly converted gamma ray followed by two others in rapid succession decaying to the stable isotope. The half-lives of the three activities are found to be 2.90, 3.35, and 6 days, respectively. T HE irradiation of normal platinum with low- PLATINUM 191 energy neutrons yields five radioactive isotopes The first assignment1 of a 3-day activity to Pt19', in platinum as well as one activity in gold. The correct from the products formed in platinum by the bombardassignment of each activity to its proper isotopic mass ment of iridium with deuterons, has proved to be a has been a difficult problem. For example, there has fortunate choice. Subsequent studies23 have shown this been no positive criterion for distinguishing between activity to yield many gamma rays, following Kcapture, the activities at masses 191 and 193. By bombarding as shown in columns 1 and 2 in Table II. The gamma iridium with either protons or deuterons both can be transitions are in iridium, following K capture in made. Fast neutron bombardments have been of value, platinum. In the present investigation most of the but since four of the activities have half-lives differing previously reported gamma rays are found, with only not greatly from 3 days, the difficulty is apparent. slight modification in their energies. However, no Only by the separation or enrichment of the less evidence can be found for the existence of gamma rays abundant isotopes of platinum can the assignments with energies of 42, 62, and 125 kevy in Pt191. In addition be made with confidence. The Oak Ridge National there appear to be gamma rays of energy 73.7 and 550 Laboratory has recently made available these separated kev, which were not previously observed. The half-life isotopes. Specimens enriched in each of the masses is found to be 2.90=t0.05 days. 190, 192, and 194 have been irradi~a~ted in the heavy- The energies of the conversion electrons taken with water pile at the Argonne National Laboratory, and various magnetic fields are summarized in columns quickly transported for studies in scintillation crystal 1 and 4 in Table I. The interpretation of each line and and magnetic photographic spectrometers. the energy sums are given in following columns. By comparing the lower-energy lines in Pt9"' with the TABLE I. Summary of electron energies for Pt"l'. similar pattern obtained with Pt193 it is possible to identify those electron lines that are due to Auger Electron Energy Electron Energy the reported Hill 12 energy sum energy Interpre- sum groups. Thus, the gamma ray reported by Hill et al.2 kev Interpretation kev kev tation kev as 62 kev is probably of this origin. No evidence 20.5 K 96.2 164.9 L1 178.2 whatever appeared to support the existence of a gamma 49.5 Auger KL1L1 168.8 3 172.0 51.0 Auger KL1L3 175.0 N 178.2 ray at 42 kev, although its L and M lines should have 53.6 K 129.6 192.9 K 268.6 been easily observed if present. The gamma reported 60.0 L1 73.7 206.0 L, 219.4 at 125 kev is probably based upon the assumption that or Auger KL1M1 216.4 31 219.5 62.2 L, 73.7 255.0 L1 268.3 the electron group at 49.5 kev is a K line. It is believed, or Auger KL3M1 274.8 K 350.9 however, that the better interpretation of this line is 69.0 L, 82.6 284.0 K 360.0 that it is of Auger origin corresponding to the very 69.8 L2 82.6 333.3 K 409.2 71.4 L3 82.7 338.0 L 351.0 strong K-L1-L1 electron group. It thus appears 79.8 MH 82.7 346.0 L 359.5 that there are, in all, fifteen gamma rays, as shown 81.8 N 82.7 356.8 M 359.9 83.4 L1.2 96.4 380.0 K 456.0 in column 3, Table II. 85.0 L3 96.4 396.0 L 409.4 The scintillation crystal spectrometer could of 93.3 M 456.0 course not resolve these gamma energies when they ~93.3 M~96.3 463.2 K 539.3 96.1 K 172.2 476.0 K 550 are close together in value. It could, however, show 102.7 K 178.6 525.5 L 539.0 11027 L, 12896 5325.5 L 539.0 broad peaks and yield valuable coincidence data. 116.0 L, 129.4 535.7 AM 5.39.0 118.3 L3 129.8 547.5 K 623.6 For example, the 172-kev gamma ray appears to be in 144.2 K 220.1 609 L 622.4 sequence with radiation at 82, 96, and 178 kev but 159.0 L1 172.5 G. Wilkinson, Phys. Rev. 73, 252 (1948). 2 Swann, Portnoy, and Hill, Phys. Rev. 90, 257 (1953). * This research was supported jointly by the U. S. Office of 3Tomlinson, Naumann, and Mihelich, Bull. Am. Phys. Soc. Naval Research and the U. S. Atomic Energy Commission. 29, No. 1, 57 (1954). 1218

1219 NEUTRON CAPTURE IN SEPARATED ISOTOPES OF Pt not with 350-kev or higher-energy peaks. By observing TABLE II. Comparison of gamma energies (kev) in Pt'91. that summations of certain of the reported energies yield other observed energies, it is readily possible Observer Swann et al.a Tomlinson et al.b Present to construct a very plausible array of levels as shown in Fig. 1, that will satisfy almost perfectly all fifteen 42 62... gamma energies. Twelve of the transitions are definitely...... 73.7 accommodated by only six levels. The three rather 82 82 82.6 94 96 96.4 weak gamma rays at 73 550 and 623 kev seem to 125 125 form a group whose ground state may be any of the 129... 129.6 other levels. If they are correctly placed in Fig. 1, 171 172 172.3 then there must be three K-capture paths from the... 220 219.7 excited platinum level. This specimen was not entirely 267 268 268.4 free from iridium as an impurity so that weak lines for 350 350 350.9 359 360 360.0 the well-known r192 spectrum were also obtained. 408 409 409.3 The ground state of Irl91 with its 77 protons and 455 456 456 537 540 539 114 neutrons has been measured to be a d1 level. The 55537 50 first excited level to be expected from shell theory... 620 623 would be an si state. If the proposed level scheme is correct, then the 82.6-kev transition should be charac- a See reference 2. b See reference 3. terized as M1. Its K electron group is too low in energy PLATINUM 193 78,Pt'9"~9~. By bombarding platinum with fast neutrons a radioactivity with half-life 3.4 days was observed5 K-PTR / / by Hole. He noted electron conversion lines for a'77'/9| -623 gamma ray of energy 126 kev and believed the activity I 77 E to be isomeric in one of the stable isotopes of platinum. 550 9 - A similar bombardment by fast neutrons, as carried KOAPTORE FIG. 1. Nuclear energy 0I 3 out by Wilkinsonl was found to yield a radioactive levels in Ir919 following 4 K capture in Pt"'. I K vca~pturerilnl ftil~ving Pt'1. 5 Io4 1Mu l ~'~ lproduct whose half-life was 4.33 days. The gamma rays 613 1 4.0 -3508 emitted were reported to have energies of 0.17 and I.3 219.7 1.70 Mev and the responsible isotope was believed to ~'1 35 [I o.926.4 be Irl93 following K capture in Pt193. More recent [ EI I |74I studies2 by Hill et al. have led to the conclusion that I l |12996 } 6.4 l 17 1 Pt193 decays by an isomeric gamma transition of I....6. I, - 82 - E- -82.6 134.9 kev, with an-assumed half-life of 4.5 days. ~-d3,/ t' r IJ 0 EIn the present investigation, the enriched Pt'92 after irradiation showed a strong low-energy gamma ray to be observed in the spectrometers but: the L1, L2, which is highly converted. The energies of the K, L1, and L3 lines are well resolved and visually appear to L3, M, and N electron lines are 57.1, 121.6, 124.0, be of almost equal intensity. The microphotometer 132.3, and 134.8 kev, respectively, indicating a gamma could not well separate the L1 and L2 peaks but showed energy of 135.5 kev. The intensity ratio for the K/L1 for the (L1+L2)/L3 ratio a value of 1.8. This is com- lines is 0.25~-0.1, and for the L3/L1 ratio, a value of patible with a mixture of M1+E2 transitions as 1.54-0.5 is found. This supports the interpretations of found4 in a very similar case in gold 195 (61 kev) by the M4 nature of this radiation. Moreover the half-life Mihelich et al. appears to be not 4.5 days but 3.35-0.1 days. This The K/L, intensity ratios for several of the remaining is in better agreement with the lifetime expected gamma rays are estimated visually as follows: 96.4 for radiation of this nature as computed from the kev (-2), 129.6 kev (-3), 172.3 kev (-5), 350.8 kev formula6 of Moszkowski. ('g9),) 360 kev (-'7), 409 kev (>10), 456 kev (''9), The scintillation crystal spectrometer showed a and 539 kev (-7). The L3/L1 ratio for the 129.6-kev high-energy gamma ray in this source in the neighborgamma is -0.12, which combined with its K/L ratio hood of 1.6 Mev. This peak seemed to decay at the and the low L2 intensity indicates that it is probably same rate as that for the 135-key gamma. Because of an M1 transition. It is possible to make assignments of the high sensitivity of the crystal detector and the the multipole order of most of these transitions, which possibility of impurities, it cannot be said with certainty make possible consistent spin assignments to the levels in Fig. 1. that this gamma ray is in Pt193. The ground state 4 Gillon, Gopalakrishnan, De-Shalit, and Mihelich, Phys. Rev. 6 N. Hole, Arkiv. Mat. Astron. Fysik 36A, No. 9 29 (1948). 93, 124 (1954). 6 S. A. Moszkowski, Phys. Rev. 89, 474 (1953).

CORK, BRICE, SCHMID, HICKMAN, AND NINE 1220 78'Pt"933so, 0,Pt'95 for the former were given as 29, 97, and 129 kev and for the latter 29, 97, and 126 kev. It was concluded that the 126-kev gamma ray was a crossover for the A 13M55 129.9 B 29- and 97-kev transitions in sequence. The 129-kev K-CAPTURE radiation was assumed to precede the others, having its origin in a metastable state of Pt'95 of half-life 3.8 P~, f_'-3 days. Each of these energies for Pt"95 appears to be __ —r-1600 X. -99.1 too low by about 2 kev. I K-CAPTURE From a consideration of our energies alone, namely, 1600 /99. 31.1 plus 99.1 being so close in value to 129.9, one would confidently but mistakenly assert that the latter is a ~do t9 — 0 Pa - 0 crossover for the other gammas. By comparing our photographic records for Pt'95 with similar plates FIG. 2. A: Transitions in Pt'93; B: level scheme for Pt'15..obtained4 by Mihelich et al. for Au195 the arrangement can be quite definitely established. His energy values of Ir193 is a d2 level so that the K capture to the ground for the 31.1- and 99.1-kev gammas agree well with ours state from a p& level in Pt'93 would be only first for- but he finds no gamma energy corresponding to their bidden. A number of gamma rays have been found7 to sum. ioreover, the relative intensity of the electron exist in Ir193 following beta emission from Os93. None lines is quite different. In Pt e fd that the L of these are observed in the present study of Pt1ga, of these are observed in the present study of Pt, (31-kev) line is considerably stronger than the K indicating that the main K-capture transition is to the, state o(99-kev) line, whereas he finds for Au"95 that the former ground state of Ir~93, as shown in Fig. 2(A). is weaker. This indicates that the 31-kev transition PLATINUM 195 precedes the 99-kev emission, so that two K-capture paths exist in the Au"95 as previously suggestedl" and Following the irradiation of normal platinum with shown in Fig. 2B. If our observed 130-kev gamma is neutrons, a group of electron lines was observed, o a cross-over transition it would have been observed which with the work functions of platinum gave two a cross-ove transition it would have been obse gamma rays with energies of 99.1 and 129.8 kev. These by Mihelich, since it is highly converted. It then energies were somewhat similar to values reported,9 seems certain that this line is in platinum and does in the decay of Au'95 (185 day), and it was thus proposed not appear in the gold decay. The K/Li and L3/L, that a metastable level probably exists in Pt"'5 with intensity ratios for the 130-kev gamma are about 0.2 a half-life of the order of 4 days. To verify this specu- and 1.7, respectively. From established" empirical lation, in the present investigation platinum enriched relations it would seem to be an M4 transition. The in mass 194 was irradiated in the pile. This specimen expected lifetime of the state would be compatible showed clearly the strong conversion electron lines with the observed half-life of the activity, which is for three gamma rays in platinum, whose energies are found to be about 6 days. 31.1, 99.1, and 129.9 kev. The electron energies with The 31- and 99-kev gamma rays are also highly their approximate intensities are shown in Table III. converted. In both cases L1 is very strong compared In a later investigation Huber et al. reported'l on the to L2 or L3, thus suggesting Mi or possibly M2 transigamma energies from both Pt'95 and Au195. The energies tions. The K/L1 ratio (2) for the 99-ke gamma TABLE III. Electron energies associated with Pt'95. would favor an M2 assignment. The half-life of an M2 state for this radiation (Z2/W=61.5) would be Electron Energy expected to be about 6 microseconds. Since coincidences energy (kev) Intensity Interpretation sum (kev) were observed between the 31- and 99-kev radiations, 17.1 32 Li 31.0 20.8 23 k 99.2 no such delay exists. Moreover, the very small L3/L1 27.8 5 Ml 31.1 intensity ratio (<0.1) favors strongly an M1 assignment. 51.6 10 K 130.0 With the scintillation crystal spectrometer peaks 85.3 13 L1 99.1 87.6 1 L3 99.1 were observed for the 30-, 60 (x-ray)-, 100-, and 95.7 5 M 99.0 130-kev gamma rays. Coincidences are observed 116.0 50 LI 129.9 118.4 85 L3 129.9 between (30, 100), (30, x-ray), (x-ray, x-ray). No coincidences could be noted between the 130-kev radiation and either of the other gamma rays. This 7 Cork, LeBlanc, Nester, Martin, and Brice, Phys. Rev. 90, 444 radiation and ei the other gamma rays. This (1953). could be due to the very high conversion coefficient" 8 Cork, Le Blanc, Stumpf, and Nester, Phys. Rev. 86, 415 (1952). 1' M. Goldhaber and A. Sunyar, Phys. Rev. 85, 733 (1952): 9 Steffen, Huber, and Humbel, Helv. Phys. Acta 22, 167 (1949). and J. Mihelich, Phys. Rev. 87, 646 (1952).'0 De-Shalit, Huber, and Schneider, Helv. Phys. Acta. 25, 279 12 Rose, Goertzel, and Perry, Oak Ridge National Laboratory (1952). Report No. 1023, 1951 (unpublished).

1221 NEUTRON CAPTURE IN SEPARATED ISOTOPES OF Pt (-800) for this radiation or to the possibility that the than the previously published values, which were 30-kev gamma is an M2 transition, so that the delay undoubtedly influenced by the presence of other would make coincidences unobservable. The very low shorter-lived radioactivities. From a comparison of the value of the L3/L1 intensity ratio for this radiation intensities of the electron lines on a sequence of plates favors but does not assure that it is an M1 transition. taken with known exposure times, the half-life appears The half-life of this radiation is considerably longer to be approximately 6 days.

VI THE ACTIVITIES OF Zn71

Reprinted from The Physical Review, Vol. 94, No. 5, 1436, June 1, 1954 The Activities of Zn71. J. M. LEBLANC, J. M. CORK,* AND S. B. BURSON, Argonne National Laboratory.-The activities of Zn71 have been investigated with a 10-channel coincidence scintillation spectrometer. Sources were obtained by the irradiation of enriched Zn70 and normal Zn in the Argonne heavy-water reactor. Two activities were found to be present in Zn71; these decay with half-lives of 2.2 min and 3 hr. The 3-hr state of Zn7l decays by the emission of beta rays followed by three gamma rays of energies 0.38, 0.49, and 0.61 Mev. The attenuation by Al of the beta rays in coincidence with each of the gamma rays was measured and found to be the same in each case and to represent a beta ray of maximum energy of 1.54-0.1 Mev. In addition each gamma ray is found to be in coincidence with the remaining two gamma rays. It is therefore concluded that the three gamma rays found in this activity are in cascade and the upper level is fed by a beta ray of 1.5 Mev. The 2.2-min state of Zn7l is found to decay by the emission of a 2.4:!:0.2-Mev beta ray which is followed by a 0.51-Mev gamma ray. Additional weak gamma rays of energies 0.12, 0.90, and 1.05 Mev were also found to be associated with this activity and to follow beta emission. Gamma-gamma coincidence studies indicate that the 0.51 and 0.12-Mev gamma rays are not in coincidence. * University of Michigan.

VII THE DECAY OF Pt199

Reprinted from The Physical Review, Vol. 95, No. 2, 627, July 15, 1954 The Decay of Pt'1. J. M. LEBLANC, J. M. CORK,* AND S. B. BURSON, Argonne National Laboratory.-The beta -and gamma rays associated with the decay of 30-min Ptm have been studied using 180~ photographic spectrometers and a l0-channel coincidence scintillation spectrometer. The beta rays were studied by measuring their attenuation in Al. Sources were obtained by irradiating normal PtO in the Argonne heavy water reactor. Nine gamma rays of energies 0.07, 0.197, 0.246, 0.316, -0.48, 0.54, 0.71, 0.0.78, and 0.96 were found to decay with a 30-min half-life and are therefore assigned to this activity. Conversion electron lines were obtained for the 0.197, 9.246, and 0.316-Mev gamma rays. The results of beta-gamma coincidence measurements indicate that the 0.197; 0.246, 0.316, and 0.54-Mev gamma-rays are in coincidence with beta rays having an end point energy of about 1.2. Gamma-gamma coincidences will be discussed. * University of Michigan.

VIII ENERGIES OF THE RADIATIONS FROM Ce144 AND Pr144

Reprinted from THE PHYSICAL REVIEW, Vol. 96, No. 5, 1295-1297, December 1, 19'54 Printed in U. S. A. Energies of the Radiations from Ce144 and Pr144t J. M. CORK, M. K. BRICE, AND L. C. SCHMID Department of Physics, University of Michigan, Ann Arbor, Michigan (Received August 16, 1954) With scintillation and magnetic photographic spectrometers the energies of the gamma rays from Ce144 have been re-evaluated. Several previously reported gamma rays are believed not to exist, while certain others not reported are found to occur. Gamma energies of 33.4, 40.8, 53.2, 59.0, 79.9, 95.0, 133.5, and 145.2 kev are found. Coincidence measurements together with a consideration of energy relationships indicate a reasonable level scheme for the Pr'44 nucleus. The energies of the three high-energy gamma rays in Nd144 following beta decay of Pr'44 are 0.688, 1.49, and 2.18 Mev. Some relative intensity measurements are made of the conversion electron lines, leading to a prediction of the multipolarities for three of the gamma transitions. The beta spectrum from Ce144 resolves into components with upper energies of 327, 258, and 160 kev. The beta radiation from Pr'44 has an upper energy limit at 3.12 Mev with a lower energy component whose maximum energy is 0.92 Mev. A LONG-LIVED radioactive cerium isotope was previously published. In Table II, the results of prefirst isolated from fission products by Hahn and vious investigations are shown together with the conStrassman' in 1940. Many subsequent investigations2 clusions of the present investigation. assigned the activity to the isotope of mass 144 and It seems quite definite that gamma rays of energy fixed the half-life at about 300 days. No evidence for 46.8, 60.3, 100, and 231 kev do not exist and that others the existence of gamma rays was presented in the at 59.0 and 145.2 do occur. This change in interpretation earlier reports. When stronger sources became available may be illustrated by the electron lines at 52.2, 53.0, from the Oak Ridge National Laboratory it was found and 57.6 kev which form a reasonable L,, L3, M group that several gamma rays accompany the beta decay of for a gamma ray at 59.0 kev. Previously the line at 53 Ce'44 to Pr'44. The Pr'44 decays mainly by beta emission kev was not resolved and had been assumed to be (-3 Mev) with a half-life of 17 minutes to the ground simply a K line for a gamma ray at 95 kev. Similarly state of Nd'44. Weak high-energy gamma radiation the M line at 57.6 kev had been assumed to be a K line accompanies this disintegration through a competing for a gamma ray at 100 kev. The line at 53 kev is as process with a very low percentage. strong as that at 52.2 kev so it is probably both an In the present investigation a fission source of high L3 line for the 59.0-kev gamma as well as a K line for specific activity was used with both scintillation and the 95.0-kev gamma radiation. magnetic photographic spectrometers to check the There is evidence for Auger lines at low energy, but previously reported results. The energies of the ob- the electron line at 26.6 kev is too low in energy to be served electron conversion lines are presented in of this nature. The electron lines which yield the gamma Table I, along with their interpretations. By carefully ray at 40.8 kev could conceivably be of Auger origin as considering each electron line in relation to its neigh- they correspond in energy to the difference in Pr work boring lines, it now appears reasonably certain that in functions, K minus L minus M, and K minus M minus several cases the gamma energies are not correct as M. However, if these rather strong electron lines are of this nature then other stronger lines should be expected TABLE I. Electron energies from Ce'44. but are not found at lower energies, corresponding to such more probable transitions as K minus L, minus L2. InterElectron Interpre- Energy Electron preta- Energy TABLE II. Summary of gamma energies from Pr'44, in kev. energy tation sum energy tion sum 26.6 kev L1 (59) 33.4 kev 57.6 kev M 59.1 kev Observer 28.5 Auger KLIL, 73.1 L1 79.9 EJKa KCb LJKo PCd Present 31.7 M 33.4 73.9 L3 79.9 34.0 L1 40.8 78.4 M 79.9 33.6 34.0 33.7 33.4 38.1 K 80.1 88.2 L 95.0 41.0 41.3 40.8 39.3 M 40.8 91.6 K 133.6 46.8 46.4'L 53.2 103.2 K 145.2 53.0 53.7 54.7 53.5 53.2 52.2 M 53.7 126.7 L 133.5 60.3 59.0 or L1 59.0 131.9 M 133.4 80.2 80.9 79.4 80.7 79.9 53.0 La 59.0 138.6 L 145.4 94.8 95.0 95.0 or K 95.0 143.7 M 145.3 99.6 100.5 100.3 134.0 134.5 134 134.2 133.5 145.2 231 t This investigation received the joint support of the U. S. Atomic Energy Commission and the Office of Naval Research. 1 D. Hahn and F. Strassman, Naturwiss. 28, 543 (1940). a Emmerich, John, and Kurbatov, Phys. Rev. 82, 968 (1951). 2 See Hollander, Perlman, and Seaborg, "Table of Isotopes," b H. Keller and J. Cork, Phys. Rev. 84, 1079 (1952). rio~iancer i-erman eaorgpe c Lin-Sheng, John, and Kurbatov, Phys. Rev. 85, 487 (1952). Revs. Modern Phys. 25, 469 (1953). d F. Porter and G. Cook, Phys. Rev. 87, 464 (1952). 1295

1296 CORK, BRICE, AND SCHMID The 80-kev peak is also found to be in coincidence with 250 - 72.7 both the 33- and 40-kev gamma with some evidence for a coincidence peak at 145 kev. 200 P / X-RAY For the 133.5-kev gamma ray the K/L conversion ratio is found to be 5.8~40.5 and the L3/L1 ratio is small o _ /- \Y (-0.1) with no L2 line present. It thus appears that 150o799 95.0 this corresponds to an M1 transition although the K/L 0 I I ratio is less than that expected from the empirical oo0100 curves of Goldhaber and Sunyar. For the 79.9-kev gamma ray the K/L ratio is 3.0=t0.5 and the L3/L, 50 _ ///I~'+ ~/ \ ratio is small (,0.15), so that this is probably an M2 50. /,+ i\ transition. The 59.0-kev gamma ray has a K/L ratio smaller than unity. If the L3 line did not have a double l 50 1 1 interpretation the L3/L, ratio would be about unity, VOLTS since the L3 line is almost as strong as the L1 with no FIG. 1. Low-energy gamma rays in PrT44, scintillation spectrometer. L2 line present. This would then be a high-order magnetic multipole transition, probably designated as The beta spectrum for Ce44 has been resolved by the aid of the double-focusing, constant-radius, magnetic Ce4 spectrometer. The high-energy electrons due to the+ 5 decay of PrM44 are always present and must be sub- \00o pt,44 tracted from the over-all distribution. The residual curve is complex and yields components with upper \ 59.0 145. energy limits at 3274-7 kev and 160415 kevy, whose. 166.9relative abundances are 75 percent and 20 percent, re- 95.0 408 spectively. There is good indication of another com- -5 335 ponent with an upper energy limit of 258~-15 kev and 327 a relative abundance of about 5 percent. There could 1 79.9 possibly still be some lower-energy component that is 133.5 79.9 not seen because of the many conversion electrons. With the scintillation spectrometer the low-energy peaks are not completely resolved. The 133.5-kev peak Nd M1 v is relatively strong as shown in the singles curve of -2.18 Fig. 1. The gamma-gamma coincidence curve between \ 2.18 the 133.5-kev gamma ray and others at lower energies 1.49 is also shown in Fig. 1. It is quite apparent that coin-.688 cidence exists and hence the upper energy level repre- O+ 0 senting the Pr'44 nucleus must be higher than 134 kev FIG. 3. Proposed nuclear level scheme for mass 144. as had been previously proposed.2 The 133-kev gamma is in coincidence with both the 33- and 40-kev gammas. M3. In this event it should not be a prompt emission but the half-life of the initial state should be of the.662 2.18-26oc order of 100 seconds. This is presumably not the case. 50C 0 CS17 }No conversion electron lines are observed that have 50 491\~~~~ X1energy differences corresponding to that of the work 40C0 || functions for neodymium. It is quite certain that the -.688 \/\2.18 -M.CI 60-kev gamma previously reported does not exist in I. ~ L / Wthis nucleus. Scintillation spectrometer observations -0300t A 1.17 2.18 of the high-energy region confirm, with some adjustCo" \ ment in energies, the previous reports.3 The singles ~2~oo2 l l J l L33 curve shown in Fig. 2 for this region yields energies at 0.688, 1.49, and 2.18 Mev. For the 2.18-Mev gamma _00 \ V \ ray, peaks due to the loss of both single and double annihilation radiation quanta are apparent. The upper energy limit of the beta spectrum is found to be at,o )0 30 40 50II 620 3.12 Mev, a value somewhat higher than the previously VOLT S FIG. 2. High-energy gamma rays in Nd'44, 3 D. Alburger and J. Kraushaar, Phys. Rev. 87, 448 (1952); scintillation spectrometer. C. Cook and W. Kreger, B3ull, Am. Phys. Soc. 29, No. 6, 20 (1954).

ENERGIES OF RADIATIONS FROM Ce144 AND Pr144 1297 reported value of 2.97 Mev. A lower-energy component to be equivalent to the sum of others, suggesting crosswith a relative abundance of 1.5 percent has its upper over transitions. It is possible to postulate a reasonable energy limit at 0.92 Mev. No strong evidence appeared nuclear level scheme for Pr144, as shown in Fig. 3, which for the existence of a beta ray at an intermediate energy, satisfies most of the observed data. The intensity relaas previously reported.3 tions as well as the coincidence data are about as would The energies of certain gamma rays are observed be expected from the level scheme.

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