ENGINEERING RESEARCH INSTITUTE TEE UNIVERSITY OF MICHIGAN ANN ARBOR PROGRESS REPORT TO JANUARY 1, 1956 INVESTIGATION OF NUCLEAR-ENERGY LEVELS J. M. ORK Professor of Physics Project 2375 OFFICE OF NAVAL RESEARCH, U. S. NAVY DEPARTMENT CONTRACT NO. Nonr 1224(13) SPONSORING AGENCY PROJECT NO. NR024-015

7ct an e eS|L| (AM AAle cgi~~Iq.

F OREWORD This group of reprints of papers published in The Physical Review during the year is submitted as a progress report for the year 1955. 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 ii

TAB LE OF C ONTENTTS Paper No. RADIOACTIVITIES OF Zn69 AND Zn7. Phys Rev., 97, 750 (1955). LeBlanc, Cork, and Burson. I 122 DECAY OF THE 3.5-min METASTABLE STATE OF Sb. Phys. Rev., 98, 39 (1955). LeBlanc, Cork, and Burson. II RADIATIONS FROM Ce143 (33 hr). Phys. Rev., 99, 670 (1955). Martin, Cork, and Burson. III ENERGIES OF THE RADIATIONS FROM Co57 AND Co58 Phys. Rev., 99, 703 (1955). Cork, Brice, and Schmid. IV RADIOACTIVE DECAY OF RUTHENIUM-97. Phys. Rev., 100, 188 (1955). Cork, Brice, Schmid, and Helmer. V NUCLEAR LEVELS IN TMm169, Lu135 AND Lu177 AS DERIVED FROM THE RADIOACTIVE ISOTOPES OF Yb. Bulletin Amer. Phys. Soc., 30, 10 (1955). Cork, Brice, Martin, Schmid, and Helmer. VI DECAY OF Ca (8.4-min). Bulletin Amer. Phys. Soc., 30, 9 (1955). Martin, Burson, and Cork. VII iii

I RADIOACTIVITIES OF Zn AND Zn7

Reprinted from THE PHYSICAL REVIEW, Vol. 97, No. 3, 750-753, February 1, 1955 Printed in U. S. A. Radioactivities of Zn69 and Zn7' J. M. LEBLANC, J. M. CORK,* AND S. B. BURSON Argonne National Laboratory, Lemont, Illinois (Received October 22, 1954) The beta and gamma rays emitted in the decay of Zn69 and Zn7' have been studied with a ten-channel coincidence scintillation spectrometer. The previous assignments of a 435-kev isomeric transition to the 14-hr Zn69 activity and a 900-kev beta ray to the 1-hr Zn69 activity were confirmed. In addition to the 2.2min activity of Zn71, a previously unreported 3-hr activity of Zn7' was detected. A beta ray with an end-point energy of 2.440.2 Mev and gamma rays with energies of 0.12, 0.51, 0.90, and 1.09 Mev were detected and assigned to the 2.2-min activity. A beta ray with an end-point energy of 1.54-0.1 Mev and gamma rays with energies of 0.38, 0.49, and 0.61 Mev were detected and assigned to the 3-hr Zn7' activity. It was established that each of the gamma rays in the 3-hr activity is in coincidence with the other two gamma rays as well as the 1.5-Mev beta ray. Decay schemes for the two Zn7' activities are proposed. T HE short-lived activities produced by neutron The present investigation is concerned mainly with capture in zinc have been previously studied with the study of Zn71. A preliminary report6 was presented varying degrees of completeness. The 14-hr and 52-min at the Detroit meeting of the American Physical activities of Zn69 had been investigated in some detail, Society. The sources were obtained by the neutron whereas the 2.2-min activity of Zn7' had been examined irradiation of both normal Zn and enriched Zn70. only by absorption and half-life studies. Zn69 had been The relative abundance of the Zn isotopes in both found to have a metastable state which decays with a normal Zn and enriched Zn70 are illustrated in Fig. 1. 14-hr half-life by the emission of a 436-kevly2 M4 Since in the enriched sample, Zn70 is enriched by a transition3 to the ground state of Zn69. The ground factor of 80, whereas Zn68 is only enriched by a factor state then decays with a 52-min half-life4 to the ground of 1.7 and all other isotopes are depleted, one can state of Ga69. The beta ray emitted by the 52-min conclude that any activity which is observed in the state had been found3 to have a maximum energy of enriched samples but not in the normal Zn samples is about 900 kev. to be assigned to Zn71. The 2.2-min activity of Zn7' was first produced by The sources were examined with a ten-channel Hughes el al.5 by neutron capture in normal Zn. By scintillation coincidence spectrometer.7 In all, four aluminum absorption experiments they determined the activities were found in the enriched Zn70 samples. maximum energy of the beta rays associated with this They had half-lives of 2.2 min, 1 hr, 3 hr, and 14 hr. activity to be 2.1 Mev. They measured the cross section for thermal neutron capture in Zn70 to be about 0.09 barn. According to the nuclear shell theory, there should exist a metastable state in Zn7' similar to the one in --- Au98 4lkeva ~435kev Zn69. One should then expect to find a second activity Zn in the Zn7' and possibly an isomeric transition between the two states. MASS'NUMBER ELEMENT 64 65 66 67 68 69 70 71 I Cu 31% 0I Zn 49% 28% 4% 18% (14 0.6%( _A W KJJ I 1 11: i X S F k \Q\ I R Ico Ga 60%, 40% nriched | Zn 10% 8% 4% 29% 48% FIG. 1. The relative abundance of the Zn isotopes. \ * University of Michi: ar, Ann Arbor, Michigan. o o 30 40 50'A. Guthrie, Phys. R v. 60, 746 (1941). VOLTS 2 B. D. Nag-Chowdhury, Proc. Nat. Inst. Sci. India 10, 317 (1944). FroIG. 2. The NaI(TI) pulse height distributions of Zn69 (14-hr) 3 R. B. Duffield and L. M. Langer, Phys. Rev. 89, 854 (1953). and the 411-kev gamma-ray of Au'98. 4 J. J. Livingood and G. T. Seaborg, Phys. Rev. 55, 457 (1939). 6 Hughes, Wallace, Goldfarb, Eggler, Murcock, and Goldstein 6 LeBlanc, Cork, and Burson, Phys. Rev. 94, 1436(A) (1954). (unpublished). 7 S. B. Burson and W. C. Jordan, Phys. Rev. 91, 498 (1953).

751 RADIOACTIVITIES OF Zn69 AND Zn7' 0.12Mev Pb X-RAY 0.44(Zn 69 800 0..44(2,69) 0 38 700Y 0.61 Mev COMPTON 0.38 600 - ~2~~~~ -~ / 5to~~0.49 ~~~~~~~~~~F400 -. NORMAL / 0.51 M.v,' SPECTRUM L B 1 0.91 Mev ~300v COINCIDENCE Sic the whh oIOSPECTRUM 0.6d 200 0 1.09Mev 100 t\ \/ 0 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 O 0.2 0.4 0.6 0.8 1.0 1.2 ENERGY IN MEV ENERGY IN MEV FIG. 4. Zn 71t (3-hr) NaI(TI) pulse-height distribution. FIG. 3. Zn7' (2.2-min) NaI(T1) pulse-height distribution. Of these, only the 1-hr and 14-hr activities were with the 2.2-min half-life. Their energies are 0.12, detected in the normal Zn sources and are thus identified 0.51, 0.90, and 1.09 Mev. The 0.51- and 0.12-Mev as the previously reported activities of Zn69. The gamma rays are by far the most intense ones in the 2.2-min and 3-hr activities must then be due to Zn71. spectrum. The results of gamma-gamma coincidence Since the Gal' which is formed by the beta decay of measurements, however, show that the 0.51- and ZnW' is stable, the fact that two activities are associated 0.12-Mev transitions are not in coincidence with each with Zn7' implies that one of them must be due to a other. The 0.90- and 1.09-Mev transitions were too metastable state in Zn7, weak for one to be able to obtain reliable gammaSince the Zn69 activities appeared to some extent gamma coincidence measurements with them. in all of the samples, it was necessary to examine their It was established that all of the gamma rays are in photon spectra, coincidence spectra, and beta rays coincidence with beta rays. The results of aluminum in order that they might be easily identified in the absorption experiments on the beta rays indicate a presence of the radiations from Znv. maximum beta-ray energy of 2.44-0.2 Mev. The slope of the aluminum absorption curve for the beta rays 1. 14-Hr ACTIVITY OF Zn69 in coincidence with the 0.51-Mev gamma ray is not The NaI pulse-height distribution from the gamma significantly different from that of the absorption rays of the 14-hr decay is shown in Fig. 2. The figure curve for single counts. Because of the rapid decay of also contains the pulse-height distribution from the the sample, however, statistics of the absorption 41 1-kev gamma ray emitted in the decay of Au'98 wdata are not good enough to allow one to determine Figure 2 is interpreted to indicate that only one gamma if there is any branching to the ground state. ray is associated with the 14-hr activity and that it has an energy of about 435 key. In addition, it was estab- 4. 3-Hr ACTIVITY OF Zn7 0 lished that the 435-key gamma ray is not in coincidence The 3-hr activity which was detected in this investiwith beta rays. This confirms the previous assignment gation and assigned to Zn71 had not been previously of the 14-hr activity to the metastable state. observed. Even with enriched isotopes, it was not possible to obtain the 3-hr activity without the presence 2. 52-MIN ACTIVITY OF Zn9 of strong 1-hr and 14-hr activities of Zn69 There were no gamma rays detected which could be The NaI(T1) pulse-height distribution obtained from assigned to this activity. Very strong beta rays were the gamma rays- of the 3-hr activity of ZnW7 is shown observed, and their maximum energy was measured by as the top curve in Fig. 4. The photopeak of the 0.435aluminum absorption experiments to be about 0.85 Mev transition of Zn69 is the dominant feature of the Mev. This agrees with previous measurements. distribution; however, another photopeak is clearly resolved at 0.61 Mev. In addition, the 0.435-Mev 3. 2.2-MIN ACTIVITY OF Zn7' photopeak is distorted on both the low- and highSamples of the 2.2-min activity of Zn7' were produced energy sides, indicating the possibility of more gamma by the irradiation of enriched Zn70 for periods of about rays being present. This region of the spectrum was 5 minutes. The half-life of the radioactivity from these examined with better resolution and the results are samples was measured to be about 2.2 min, in good shown in the inset of Fig. 4. It is clear, from these agreement with previous results. The gamma-ray data, that the peak at about 0.44 Mev is complex. spectrum was obtained by means of the scintillation In order to examine this region without the presence spectrometer and is shown in Fig. 3. The photopeaks of the Zn69 gamma ray, the pulse-height distribution for four gamma rays are identified and found to decay of gamma rays which are in coincidence with beta rays

LEBLANC, CORK, AND BURSON 752 was determined (see bottom curve of Fig. 4). The Gamma-gamma coincidence experiments were perpeaks which occur in this spectrum at 0.38, 0.49, and formed with the three gamma rays in this decay. The 0.61 Mev are interpreted as photopeaks of gamma rays results are shown in Fig. 5. The positions of the three of these energies. The peak at about 0.17-0.20 Mev is gamma-ray photopeaks in the pulse-height distribution interpreted as due to Compton electrons and Compton- were determined from the beta-gamma coincidence scattered gamma rays. The rate of decay of each of pulse-height distribution shown in Fig. 5(a). The these peaks was determined and found to correspond single-channel analyzer was then set to cover one of the to a half-life of about 3 hr. regions bounded by the dotted lines, and the ten-channel The source was allowed to decay for one day, and analyzer swept across the 0.30- to 0.65-Mev region of then another normal pulse-height distribution was the distribution. The resulting coincidence distributions determined. The only activity which remained was that are shown as curves b, c, d, e, and f in Fig. 5. It can be of the 14-hr Zn69. This pulse-height distribution was seen from these curves that each gamma ray is in then normalized, at the 0.44-Mev peak, to the pulse- coincidence with the other two; thus, the three transiheight distribution of the previous day and subtracted tions are in cascade. from it. The resulting distribution was the same as that of the gamma rays in coincidence with beta rays 5. DECAY SCHEME OF Zn71 which was obtained the first day. Thus, it is concluded The present investigation has confirmed the predicthat all of the gamma rays which were found in the tion of the nuclear shell theory that a metastable state 3-hr activity are in coincidence with beta rays. should exist in Zn71. It has not been possible, however, The maximum energies of the beta rays which are in to determine from the data which of the two activities coincidence with the 0.38, 0.49, and 0.61-Mev gamma is due to the ground state. For this reason the suggested rays were determined by measuring the attenuation of~ decay schemes of the two activities are shown the beta rays in aluminum. It was established that separately. See Fig. 6. The decay scheme of the 3-hr each gamma ray is in coincidence with a single beta ray activity is strongly supported by the beta-gamma and whose maximum energy is 1.5-0.1 Mev in each case. gamma-gamma coincidence measurements. There is no his s s g s t t ee g ase. information to indicate in what order the three gamma This strongly suggests that the three gamma rays are rays are emitted; the lowest energy transition is arbitrarily placed at the bottom. The portion of the decay scheme of the 2.2-min 0. SPECTRUM OF 3hr state which is indicated by solid lines is confirmed by GAMMA RAYS IN COINCIDENCE WITH C coincidence measurements. The portion of the level 0.4 9 l scheme represented by dashed lines is based entirely on the energies of the transitions. The energy of the I I/ I 1.09-Mev gamma ray does not agree very well with I 0. 611 | the sum of the 0.12- and 0.91-Mev transitions. This I/ | 10 is not considered to be a serious objection since the fI i I d | V i\accuracy of measurement of the energy of the 1.09-Mev I A 8 B 1 C I D I E l \ transition is rather poor, due to the very low intensity of the peak. There may be additional beta transitions J IN COINCIDENCE WITH A IN COINCIDENCE WITH D to the 0.12-Mev level and to the ground state. It is difficult to understand why there are no common Cr ~ I states in Ga7' in the two decay schemes. One might I- 1/\ I Zn7' Zn7I 30 30 4~ (3H) 2.2 M) 1.5 0.1Mev \ IN COINCIDENCE WITH B IN COINCIDENCE WITH E lGa7 CGO I G' 2.4 0.2\ \ 3a Mov 3 ~C I/ ~~ t 4 —1.09 I T7 0.49Mev Mev 0.40 0.50 0.60 0.40 0.50 0.60 I ENERGY Mev ENERGY Mev -.Mv _ —' FroIG. 5. Zn7' (3-hr) gamma-gamma coincidences. FIG. 6. Decay schemes of Zn7'M and Zn71.

753 RADIOACTIVITIES OF Zn69 AND Zn7' suspect that the 0.49-Mev transition which follows the common states in the two decay schemes might be 3-hr beta decay is the same as the 0.51-Mev transition due to some selection rule other than those arising in the 2.2-min decay. In order to check this, the energies from the conservation of total spin and parity. of the two transitions were compared without altering The total energy of the Zn7l decay is measured to be the spectrometer settings. It was determined that there about 2.9 Mev. This value is in good agreement with were indeed two distinct gamma rays with energies that predicted from the beta decay systematics.8 that differed by about 0.03 1Mev. The absence of 8 K. Way and M. Wood, Phys. Rev. 94, 119 (1954).

II DECAY OF THE 3.5-min METASTABLE STATE OF Sb

Reprinted from THE PHYSICAL REVIEW, Vol. 98, No. 1, 39-40, April 1, 1955 Printed in U. S. A. Decay of the 3.5-min Metastable State of Sb122 J. M. LEBLANC, J. M. CORK,* AND S. B. BURSON Argonne National Laboratory, Lemont, Illinois (Received November 4, 1954) The radiations associated with the 3.5-min activity of Sb122 have been studied with 1800 magnetic photographic spectrometers and a ten-channel coincidence scintillation spectrometer. Two gamma rays with energies of 60.7 and 75.3 kev were detected by means of internal conversion electrons and also by means of the scintillation spectrometer. The 75.3-kev transition is the more strongly converted of the two, and it is concluded that it is the isomeric transition. The two gamma rays are emitted in cascade. AN isomeric state in Sb'22 was first reported by der groups, one employing a scintillation spectrometer2 and Mateosian et al.l in 1947. They measured its the other an ionization chamber.3 The results of the half-life to be 3.5 min. The gamma rays associated scintillation spectrometer study indicated the presence with the 3.5-min decay have been investigated by two of one gamma ray with an energy of 68 kev, whereas X- RAY.27kev (A) SMALL CRYSTAL (B) LARGE CRYSTAL IW FIG. 1. NaI(Tl) pulse-height 71 kev distributions of gamma rays cc from Sb22mn. Goh63ekevr X-RAY OF TY,:: 60 kev x 4 I Ib x? H. ak RgNiae Ske N.191 (pb75kev 10 20 30 40 30 40 50 VOLTS * University of Michigan, Ann Arbor, Michigan. der Mateosian, Goldhaber, Muehlhause, and McKeown, Phys. Rev. 72, 1271 (1947). 2 E. der Mateosian and M. Goldhaber, Phys. Rev. 82, 115 (1951).'J. H. Kahn, Oak Ridge National Laboratory Unclassified Report ORNL-1089, Nov. 1951 (unpublished).

40 LEBLANC, CORK, AND BURSON TABLE I. Internal conversion electrons associated ably weaker than that of the 60-kev transition. Since with the decay of Sb22m. the internal conversion electron lines of the 75-kev transition were stronger than those of the 60-kev Electron line Energy sum energy (in kev) Interpretation (in kev) gamma ray, one concludes that the 75-kev radiation 30.2 K' 60.7 is the more strongly converted of the two. The 75-kev 45.1 K2 75.6 gamma ray is therefore identified as the isomeric 70.2 LI2 74.9 transition. From the energy lifetime relations for 70.9 LII12 75.0 gamma rays, it is concluded that the 75-kev radiation has a multipolarity of 3. the results of the ionization chamber study indicated 122 m the presence of two gamma rays with energies of 59 51 Sb and 74 kevy. (3.5min ) The Sb122m sources which were used in the present investigation were obtained by the irradiation of enriched Sb121 in the Argonne Heavy Water Reactor (CP-3'). They were examined with both 180~ magnetic 75.3 kev photographic spectrometers4 and a ten-channel coin- E3or M3 cidence scintillation spectrometer.5 Four internal conversion electron lines were detected with the 180~ spectrographs. They are listed in the first column of Table I. They are interpreted as internal conversion FIG. 2. The decay scheme of,,Sbi2" (3.5-min). electrons from gamma rays with energies of 60.7 and 75.3 kev. The electron lines for the 75.3-kev gamma ray are much stronger than the K line of the 60.7-kev 60.7 key transition. The NaI pulse-height distribution produced by the gamma rays from Sb122m is shown in Fig. 1(a). The peaks decayed with a half-life of about 3.3 min. The _ (2.8d) low-energy peak, at about 27 kev, is due to the x-rays of Sb. The other peak is quite broad and is distorted on the high-energy side, indicating that it is due to more than one gamma ray. This peak was examined with better resolution and the resulting distribution is shown in Fig. 1 (b). The strong component of this peak Coincidences were observed between the x-ray and occurs at about 63 kev, and the distortion of the high- the 60-75-kev peak. Since the x-rays are produced as a energy side indicates the presence of a gamma ray consequence of the internal conversion of one of the with an energy in the neighborhood of 75 kev. This gamma rays, one should not observe x-ray gamma-ray agrees with the internal conversion data. coincidence unless the two gamma rays are in cascade. The photopeak of the 75-kev gamma ray is consider- It is concluded from these experiments that the -4H. Keller, and J. M. Cork, Phys. Rev. 84, 1079 1951 3.5-min metastable state decays by means of a 75-kev Rutledge, Cork, and Burson, Phys. Rev. 86, 775 (952). (195); isomeric transition which is followed by a 60-kev R utledge, Cork, and Burson, Phys. Rev. Re. 86, 775 (1952). 5 S. B. Burson and W. C. Jordan, Phys. Rev. 91, 498 (1953). transition as shown in Fig. 2.

III RADIATIONS FROM Ce143 (33 hr)

Reprinted from The Physical Review, Vol. 99, No. 2, 670, July 15, 1955 Radiations from Cel43 (33 hr).* D. W. MARTIN, J. M. CORK, AND S. B. BURSON, Argonne National Laboratory.The radiations from Ce'43 (33 hr) have been studied with the scintillation coincidence spectrometer and with magnetic photographic spectrographs. Enriched Ce'42 was irradiated with reactor neutrons. Gamma rays of 1.10-0.01, 0.861 ~0.005, 0.724=0.002, 0.668 ~0.002, 0.565i~0.005, 0.493 ~0.002,,0.351I0.001, 0.294~0.001, 0.23240.001, and 0.0574~=!0.0002 Mev are found to decay with the 33-hr period in the NaI (Ti) pulse-height distribution. Conversion lines are seen for all but the 1.10- and 0.57-Mev transitions. Gammagamma and beta-gamma coincidence data define the decay scheme with considerable certainty. The Pr'43 nucleus is shown to have excited states at 0.0574, 0.232 (or 0.493), 0.351, 0.724, 0.918, and 1.16 Mev. Qualitative observations of the beta-ray components were made by observing the pulseheight distributions from an anthracene crystal in coincidence with the principal gamma components. In addition to the known strong components at 1.38, 1.09, and 0.71 Mev, two distinct weak components at -0.5 and -0.3 Mev are observed, coincident with radiations from the 0.918- and 1.16Mev levels respectively. The pulse distribution coincident with the 57-kev gamma ray is indistinguishable from the noncoincidence distribution above 1 Mev. Thus, the 1.38-Mev beta ray feeds the 58-kev level, and any ground-state beta transition is of low intensity. * Work done under auspices of U. S. Atomic Energy Commission.

IV ENERGIES OF THE RADIATIONS FROM Co57 AND Co58

Reprinted from THE PHYSICAL REVIEW, Vol. 99, No. 3, 703-705, August 1, 1955 Printed in U. S. A. Energies of the Radiations from Co57 and Co58t J. M. CORK, M. K. BRICE, AND L. C. SCHMID Department of Physics, University of Michigan, Ann Arbor, Michigan (Received March 28, 1955) Using magnetic and scintillation spectrometers the energies of the radiations from Co57 and Co58 have been evaluated. Several gamma rays not previously reported have been observed. Co57 decays mainly by K capture but also to a slight extent by positron emission with an upper energy limit of about 300 kev, followed by gamma rays with energies 14.6, 29, 99.8, 122.8, 137.4, and 700 kev. Co5s decays by K capture and with positron emission of upper energy 485+10 kev. Gamma rays with energies of 814 and 500 and possibly 1300 kev accompany the decay. AS early as 1937 it was found' that iron bombarded addition to these three gamma rays, others appear with deuterons in the cyclotron yielded several with energies of 700, 99.8, and 29 kev. These additional long-lived cobalt radioactivities. Subsequent investiga- gamma rays are observed with the scintillation spections2 resulted in the assignment of activities with half- trometer. Of them, only the 99.8-kev gamma appears by lives of 270 and 72 days to Co57 and Co58, respectively. conversion and this with a single line assumed to be due The reports on the energies of the radiations show con- to Fe K-electrons. siderable disagreement indicating a need for further For the three gamma rays shown in Table I, many study. electron lines are observed whose energies and relative In the present investigation magnetic photographic, intensities are shown in Table II. The relative intensities and scintillation spectrometers were employed to study for the lines due to the 14.6-kev gamma ray are from gamma rays, and the double-focusing, magnetic spec- visual estimates of the photographic densities, corrected trometer was used to observe the positron spectrum of for variation in radius and sensitivity of the emulsion Co58. In addition to the gamma energies previously with energy. The intensities for the other two gamma recorded certain gamma transitions not previously rays were obtained both by microphotometer traces of reported are observed. The Co57 source was obtained the photographic plates and by comparing the resolved from the Oak Ridge National Laboratory and was peaks obtained with the source in the double-focusing produced by a p,2n reaction on Ni58 in a target of spectrometer. The 14.6-kev in Fe57 has been reporteda ordinary nickel. The resulting Cu57 in turn decays by to have a half-life of 1.1X 10-7 sec and the transition positron emission through Ni57 to Co57 and thence to to the ground state was assumed4 to be MI. The Z2/W Fe57. The Co58 specimen was from the same source but for this radiation is 46.2. From the empirical summary produced in the reactor by the (n,p) reaction on Ni58. of Goldhaber and Sunyar, the observed K/L ratio of It decays mainly by K capture but also by weak 3 appears to be somewhat lower than expected for an positron emission to Fe58. M1 transition. It would seem to be more compatible with an El or an M2 transition. The lifetime for the COBALT-57 M2 transition at this energy would be of the order of Some of the previously reported energies for the seconds and this designation is thus improbable. three well-known vigama.ras rtoet ergwites forelts The large values of the K/L ratios for the 122.8- and three well-known gamma rays, together with the results 137.4-kev gamma rays suggest El, E2, M1, or M2 of the present investigation, are shown in Table I. In 1 4 g transitions. The half-life of the M2 transition would TABLE I. Gamma energies of Co67 as reported, in kev. TABLE II. Energy and relative intensity of electron conversion lines from Co57. Present Observer pa EDb DWc AGd CMe work Electron Energy 1l 117 119 122.8 119 122.8 energy, Relative sum, 72 130 131 137.6 133 137.4 Designation kev intensity kev 73 14 14.6 K1 7.3 3 14.4 - _-_:_-_L1 13.7 1 14.6 a E. H. Plesset, Phys. Rev. 62, 181 (1942). M1 14.5 0.25 14.6 b E. Elliott and M. Deutsch, Phys. Rev. 64, 321 (1943). K 92.7 99.8 o M. Deutsch and W. Wright, Phys. Rev. 77, 139 (1950). K2 115.7 10 122.8 d D. Alburger and M. Grace, Proc. Phys. Soc. (London) A67, 280 (1954). L 121.8 0.9 122.7 e B. Craseman and D. Manley, Phys. Rev. 98, 279 (A) (1955). M2 122.7 015 122.8 Ms 122.7 0.15 122.8 Ka 130.3.8 137.4 t This investigation received the joint support of the U. S. K3 130.3 8 137.4 Atomic Energy Commission and the Office of Naval Research. 1Livingood, Seaborg, and Fairbrother, Phys. Rev. 52, 135 (1937)..... 2 Hollander, Perlman, and Seaborg, "Table of Isotopes," 3 M. Deutsch and W. Wright, Phys. Rev. 77, 139 (1950). Berkeley (1952). 4 M. Goldhaber and A. Sunyar, Phys. Rev. 83, 906 (1951). 703

704 CORK, BRICE, AN:D SCHMID 27CO53O this high energy. The well-established transitions are shown as heavy lines in the nuclear level scheme of G57 K' /2 Fig. 1. The 99.8-kev transition is not included. 26Fe31 / The half-life of the Co57 sample observed over a I -- -" -- / period of 8 months appears to be 267 days. COBALT-58 K 700 Co58 decays by both K capture and positron emission to Fe58. A single gamma ray of energy 0.81 Mev had been reported.2 In the present investigation this gamma ray is observed both by electron conversion and by the 1374 scintillation spectrometer. The K-conversion line has an energy of 807 kev, indicating a gamma energy of 137.4 22.8 - 814 kev. The L line is very weak so that the K/L ratio E2 Ml is exceedingly large. It is impossible to infer from this FOR ratio the type of multipole radiation, since at this small --- T — Z2/W (0.8), the K/L ratio is large for all types of 1 29 el4.6 Mi OR El,4. radiation. However, the ground state for the even-even -,0 oke 26Fe58 nucleus is undoubtedly a level of even parity and FIG. 1. Nuclear level scheme for Fe57. zero spin. In such nuclei the first excited state is usually one of even parity and spin 2, so that an E2 transition still be of the order of a thousandth of a second and is expected. hence should probably be excluded. While the K-con- The Co58 source also contains some Co60 with its version lines for the two gamma rays are of the same long-lived radiation at 1.17 and 1.33 Mev. With the order of darkness and their K/L ratios are about the scintillation spectrometer, strong peaks are obtained same, it is observed that the unconverted peak at at 500 and 800 kev, and a weaker peak at 1.3 Mev. 122.8 kev is many times5 ~stronger than the peak at The 500-kev peak was at first assumed to be annihilation 137.4 kev. Hence, if the absolute conversion coefficient radiation. On observing coincidences between all betas for the 137-kev gamma ray is ten times that for the in an anthracene crystal, and the gamma distribution 123-kev gamma ray, then the former is probably due in a NaI crystal, the 500- and 800-kev peaks were to an E2 and the latter to an El or M1 transition. The present in about the same relative intensity. On obpositron spectrum was found to be extremely weak, serving gamma-gamma coincidences with one crystal with an upper limit of about 300 kev. It was not resolved into the two components reported.6 The 29-kev peak was found to be in coincidence with both the 100- and 700-kev radiations but not with the 350 w 123- or 137-kev gammas. No coincidences could be observed between the 700- and the 100-, 123-, or 137-kev 0,o kev radiations. It should be noted that coincidences as ob- 30 GEOMERY served might result from the iodine x-ray (28 kev) 5 escaping from one crystal back to the opposite crystal, \ resulting in an apparent peak due to the true peak 250 \ energy minus the x-ray energy. Evidence that the low- J \ f energy peak is a gamma ray comes from the fact that it " M5 Al appears in the "singles" curve when there is no idoine 2 or other scatterer back of the source. When iodine is A- SINGLES, COINCIDENCES intentionally placed directly back of the source the WBNCIDTH 510 peak shifts slightly toward lower energy. Moreover, IA the 100-kev gamma ray yields a conversion line. The weak 700-kevy transition probably follows K capture, t00 and from the coincidence observation it might be concluded that it terminates at a level other than the I ground state although this evidence is not incontrovertible. The escape peak is less likely to be significant at 6 D. Alburger and M. Grace, Proc. Phys. Soc. (London) A67, 40 50 60 280 (1954). V.LTS 6 B. Craseman and D. Manley, Phys. Rev. 98, 279 (195'5). FIG. 2. Coir]ldene dat4 for Co58, with crystals at right angles.

RADIATIONS FROM Coa7 AND Cos8 705 set to receive the 500-kev peak, again the other crystal 27C noted the two peaks in the same relative intensity. 2-7Since the annihilation photons travel in opposite direc- / 2Lc tions and could yield 500-500 kev coincidences, the crystals were arranged at right angles with the source as shown in Fig. 2. The singles and coincidence curves 485 are represented by solid and dotted lines, respectively, strongly indicating the existence of a gamma ray of about 500-kev energy. The peak at 1.3 Mev could be a summation peak for the other gamma rays or represent a crossover transition, or be in part due to the L3 500 slight amount of Co60 that is known to be present. On l inserting about 2 cm of lead between source and crystal.814 the intensity is reduced much more than would be the case if it were all 1.3-Mev radiation, with its absorption coefficient of 0.66 cm-1. This indicates that it is largely.814'~...0 Mev FIG. 4. Nuclear level scheme for Fe58. k\ a summation peak, but in part it may be due to a cross-over transition. ~K The positron spectrum was investigated in the double-focusing spectrometer and was found to have only one component. The almost massless source conFN~'l sisted of a line of the carrier-free material ruled on a \ conducting zapon film. The spectrometer window, also of zapon, was of minimum thickness (about 15 micrograms per cm2) to withstand a pressure difference of 6 or 7 cm of Hg. The linearity of the Fermi plot, shown in Fig. 3, down to very low energies, indicates the very small stopping power of the film. The upper energy limit is 485-10 kev. If the positron decay occurs for about 15 percent of the decays, then the logft value is }I about 6.5, which indicates a first forbidden transition. The simple decay scheme is shown in Fig. 4. The halfo~-'oo!800 3~o~-~j00 400 \- life of the Co58 source corrected for the presence of a Rev slight amount of longer-lived activity is found to be FIG. 3. The Fermi plot for the positron spectrum of Co68. 71.0 days.

V RADIOACTIVE DECAY OF RUTHENIUM-97

Reprinted from THE PHYSICAL REVIEW, Vol. 100, No. 1, 188-190, October 1, 1955 Printed in U. S. A. Radioactive Decay of Ruthenium-97t J. M. CORK, M. K. BRICE, L. C. SCHMID, AND R. G. HELMER Department of Physics, University of Michigan, Ann Arbor, Michigan (Received June 6, 1955) Ruthenium enriched in mass 96 was irradiated for short and long periods in the pile and the radioactivity of Ru97, produced by neutron capture, was studied by magnetic and scintillation spectrometers. Several gamma rays not previously reported were found to exist. The observed gamma rays in Tc97, following K capture in Ru97, have energies of 109.1, 216.1, 325.1, and 570 kev. A long-lived metastable state in Tc97 decays by the emission of gamma rays whose conversion electrons indicate gamma energies of 90.2 and 99.2 kev. The multipolarities of most of the transitions are determined and a satisfactory nuclear level scheme is proposed. BY the bombardment of ruthenium with both not previously reported. Since the separated Ru96 deuterons and neutrons an activity of half-life 2.8 specimen contained about 1%0 of Ru102, the welldays was observed1 and attributed to Ru97. A single known gamma rays for Ru103 were found to be present gamma ray following K capture had been noted with an but weak. There was also a very weak iridium impurity energy variously'reported to be 0.2301 or 0.2172 Mev. in the separated Ru isotope, so that its well-known This transition, following K capture, should occur in spectrum was faintly observed. The half-life of the Tc97, presumably leading to a reported3 metastable Ru97 activity, was followed through more than eight level whose half-life has been given as 90 to 95 days. octaves and was found to be 2.44 days, or 58.6 hours. A gamma ray with an energy somewhere between 96 The energies of the observed electron conversion and 108 kev had been found to be associated with lines, exclusive of those due to Ru103 and Ir192, are Tc97m. presented in Table I. The interpretation of each line In the present investigation a specimen of ruthenium, is given in the second column and where possible the enriched in mass 96 from its normal 5.7 percent up to relative intensities are presented in column 3. From 95.5 percent, was irradiated in the maximum flux of these observations it can be concluded that there are the Argonne heavy water pile. In order to distinguish at least four gamma rays associated with the 2.44-day the lines due to Ru97, both short (3-day) and long radiation, with energies of 109.1, 216.1, 325.1, and 570 (30-day) irradiations were made. Radioactive sources kev. These energies were also observed as peaks with were studied in photographic magnetic and scintillation the scintillation spectrometer on "singles" studies, spectrometers. Strong electron conversion lines were with the exception of the 109.1, which does, however, observed indicating the presence of several gamma rays appear in strong coincidence with the 216.1. Coincidences between the 216.1- and 325.1-kev gammas are TABLE I. Energies and relative intensities of the not observed. The spectrum in coincidence with the electron lines from Ru97... Tc K x-rays is identical with the "singles" spectrum out to 400 kev; coincidence work with the 570-kev Electron Energy energy, sum, peak was inconclusive because of its extreme weakness. kev Designation Intensity kev Curve A of Fig. 1 shows the "singles" spectrum and 15.1 Auger KLL1 curve B shows the spectrum in coincidence with the 15.5 Auger KL2L2 216.1-kev gamma ray. The photopeaks and conversion 17.9 Auger KLM 20.1 Auger KMM lines for these four gamma rays, observed over a period 69.2 K(Tc97m) 90.2 of time, all appear to die out with the same half-life. 78.2 K(Tc97m) 99.2 The absence of an annihilation peak at 511 kev in the 88.1 K 3 109.1 89.0 L (TC97m) 92.0 scintillation spectrum and the negative result of a 97.8 L(Tc97m) 100.8 search for positrons with the magnetic double-focusing 106.1 L 100 209.1 spectrometer indicate that Ru97 decays principally, if 213.1 L 14 216.1 not entirely, by K capture. 215.4 M 215.9 In the specimen irradiated for 30 days, the long-lived 303.9 K 8 325.0 322.2 L 1 325.2 Ru103 and the Ir192 electron lines appeared relatively 549 K 570 much stronger in comparison with the lines due to the 2.44-day Ru97. However, certain new lines were evident which were not due to either of the above contaminants t This investigation received the joint support of the Office of Naval Research and the U. S. Atomic Energy Commission. but which appeared to have a long half-life. Successive 1 Sullivan, Sleight, and Gadrow, Phys. Rev. 70, 778 (1946). exposures showed that after the Ru97 short-lived 2 Mei, Huddleston, and Mitchell, Phys. Rev. 79, 429 (1950). activity died out there still remained two pairs of 3 Hollander, Perlman, and Seaborg, Table of Isotopes, Berkeley, activity died out, there still remained two pairs Of 1952 [Revs. Modern Phys. 25, 469 (1953)]. electron lines with energy differences characteristic 188

189 RADIOACTIVE DECAY OF Ru97 of the K and L work functions for Tc. Figure 2 shows (a) a plate made after the 3-day irradiation, (b) one made immediately following the 30-day irradiation, and (c) one made two weeks after the 30-day irradiation, (a) when the 2.44-day activity had largely died out. It seems likely therefore that this is the radiation previously observed3 to be associated with a metastable TcOTi, whose half-life was noted to be from 90 to 95 days. No attempt was made to verify this half-life, or (b) that of the ground state of Tc97(-104Y). The energies of these gamma rays are 90.2 and 99.2 key, and their K/L conversion ratios are both approximately unity. They are of about equal intensity as judged by the density of their K conversion lines, and (c) are both highly converted, as they hardly appear in the 216 FIG. 2. Internal conversion spectra of TC97 and Tc7m for short- and long-period irradiations. and 6.7:t0.6, respectively. The 109.1-key gamma has ENERGY I K w a high conversion coefficient, as it appears only weakly in the scintillation spectrometer although strong conversion lines are observed. Measurements of the relative intensities of both the photopeaks and K conversion lines of the 216.1- and 325.1-key gammas indicate that the ratio of their K conversion coefficients must be approximately unity. The fact that the 216.1key gamma is much stronger than the 109.1, both converted and unconverted, shows that the 216.1 follows the 109.1 and is supplied by an additional K capture branch whose degree of forbiddenness is no 109 570 91Ru 325 2440 f 40 ~Tc97 0 -1b 30 40 50 60 43 54 VOLTS FroIG. 1. Singles and coincidence spectra for Tc97 with the scintillation spectrometer. scintillation spectrum. The high conversion coefficient, low K/L ratio, and long half-life indicate that these are high-order multipole transitions, probably E3 or M4. 9 i- 424 According to shell theory the ground state of Tc97 is 570 w9J / expected to be a g9/2 level and the first excited state a Pl/2 level. The difference in energy of these two gamma 35.3 rays, namely 9 key, suggests the existence of two lowlying states such as gs/ and 7/2+, as has been reported4 325.1 216.1 to exist in Tcm. 2 MI The relative intensities of the electron lines associated P[L 1.2 90 with the 2.44-day activity were determined from 90.2. microphotometer traces of the photographic plates, - + — M4 (.104 y) corrected for variations in radius and emulsion sensi- K~ tivity with energy. The K/L ratios for the 109.1-, / 216.1-, and 325:.1-kev gammas are 3.0ht0.6; 7.3q-0,3, 4 Mihelich,: Goldhiaber, and Wilson, Phys.:Rev. 83, 216 (1951). FIG. 3. Nuclear level scheme for Tc'7.

CORK, BRICE, SCHMID, AND HELMER 190 greater than that of the K capture branch followed by transitions are, respectively, E2, M1, and E2. The the 109.1 transition. It is known from the coincidence 570-kev gamma probably follows another weak K data that the 216.1- and 325.1-kev radiations have capture branch, but its terminal level is uncertain. A half-lives shorter than about 10-6 sec, and the half-life nuclear level scheme for Tc97 consistent with the above of the 109.1 must be of the same order of magnitude information is shown in Fig. 3. as that of the 325.1. A comparison of the measured Note added in proof.-A consideration of the exK/L ratios with the empirical curves5 and of the information on conversion coefficients with the theoretical pected half-lives for the 9-, 90.2-, and 99.2-key transimation on conversion coefficients with the theoretical tions indicates the possibility of interchanging the order values' indicates that the 109.1-, 216.1-, and 325.1-kevy of the 9- and 90.2-kev gammas. The 9-kev transition 5M. Goldhaber and A. Sunyar, Phys. Rev. 83, 906 (1951). would then b e interpreted as. The 9-ke the 0.2-kev 6 Rose, Goertzel, and Perry, Oak Ridge National Laboratory be interpreted as E3 and the 90.2-key Report ORNL-1023 (unpublished). transition as of lower multipole order.

VI NUCLEAR LEVELS IN Tm169 Lu35, AND Lu77 AS DERIVED FROM THE RADIOACTIVE ISOTOPES OF Yb

Reprinted from the Bulletin of the American Physical Society, Vol. 30, No. 7, 10 (1955) Nuclear Levels in Tm169, Lu'75, and Lu'77 as Derived from the Radioactive Isotopes of Yb. J. M. CORK, M. K. BRICE, D. W. MARTIN, L. C. SCHMID, AND R. G. HELMER, University of Michigan.-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 re-evaluation of the energies of the radiations has been made. Several previously unreported gamma rays are found and nuclear level schemes for Tm169, Lu175, and Lu'177 proposed. Several of the levels appear to be rotational states in the unified nuclear model. Yb169 decays with a half-life of 30.6 days by K capture, followed by eleven gamma rays in Tm169. 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. Ybl75 decays with a halflife of 4.2 days by beta emission (474 kev max) followed by five gamma rays in Lul'75. 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. Yb177 decays with a half-life of 1.88 hours by beta emission followed by gamma transitions in Lu177. 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 Lu177, if present at all, is too weak to be observed by the magnetic spectrometers, which suggests some possible error in the assignment of masses in the stable isotopes. V70y69 70' 99 K / / T-169 K K 69 I T'100 K _- X z/-I380.0 / 63.2 / / / -/ 316.8/ 2 61.0 / / 17.7 / / 19. B.6 - 211.9 93.6 1- 1 20.6 1~39.1 136.6 if ", } l 118.3 118.8 1307 109.9 118.3 i+'' 8!4 n'l 8.4 8.4 0 0 OBSERVED CALCULATED

VII DECAY OF Ca ( 8.4-min )

Reprinted from the Bulletin of the American Physical Society, Vol. 30, No. 7, 9 (1955) Decay of Ca49 (8.4-min).* DAVID W. MARTIN, S. BRADLEY BURSON, AND JAMES M. CORK, Argonne National Laboratory.-The beta and gamma radiations of radioactive Ca49 have been studied with the Argonne 256-channel coincidence scintillation spectrometer. Sources were prepared by irradiation in the Argonne reactor (CP 5) of samples enriched to about 12% in Ca48. Gamma rays of 3.2440.05 and 4.30== 0.05 Mev were observed to decay with the 8.4i0.1-minute period in the NaI (TI) pulse-height distribution, in which a well collimated geometry was used. The 4.30-Mev gamma ray has an intensity of about 5% that of the 3.24-Mev transition. Calibration was based on the 4.45-Mev gamma ray of C12 excited by an (%n) reaction in a shielded Po-Be source.1 A beta ray with an end-point energy of 1.934-0.10 Mev is found to be in coincidence with the 3.24-Mev gamma ray from a coincidence absorption curve. A softer beta ray in the neighborhood of 1 Mev is in coincidence with the 4.30-Mev gamma ray. The indicated decay energy of 5.14-0.2 Mev is consistent with the beta decay systematics of this region of the nuclide chart.2 * Work performed under auspices of U. S. Atomic Energy Commission. 1 R. J. Breen and M. R. Hertz, Phys. Rev. 98, 599 (1955). 2 K. Way and M. Wood, Phys. Rev. 94, 119 (1954).

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