G.E. Gordon

Ranges of fragments from fission of U235 with thermal neutrons and the kinetic energy deficit

Abstract Differential- and average-range measurements have been made on several fission-product recoils in aluminium from fission of U 235 with thermal neutrons. The observed average ranges are, in mg/cm 2 Al: Mo 99 , 3.98±0.02; Ag 111 , 3.55±0.01; Cd 115 , 3.32±0.01; Sn 121 , 3.18±0.02; Sn 125 , 3.21±0.01; Sb 127 , 3.25±0.01; Sb 129 , 3.34; Ba 140 , 2.98±0.01. Resolution of the range distributions, defined as full width at half maximum divided by average range, after removal of various experimental effects, runs from 10±5% (Mo 99 ) to 18±5%(Cd 115 ). Ranges of the fragments were converted to energies in order to determine the magnitude of the deficit in total kinetic energy release at symmetric fission, which we found to be 21 MeV. From the range-dispersion data, we find that the dispersion in total kinetic energy release is not as great in the symmetric region as has been previously indicated by time-of-flight experiments. We find no indication that the kinetic energy deficit at symmetric fission is connected with the two-mode fission hypothesis which has been successful in explaining energetics of fission induced at higher energies.

Decay scheme of 13.3 h 123I

Abstract The decay scheme of 13.3 h 123 I to levels of 123 Te has been determined with the use of Ge(Li) and NaI(Tl) γ-ray detectors and coincidence equipment. Sources were produced by the 121 Sb(α, 2n) 123 I reaction. A total of 14 γ-rays was observed and placed in the decay scheme. Excited states of 123 Te were established at 159, 248 (117 d 123m Te), 440, 506, 688, 698, 784 and 895 keV. The upper limit for position decay of 123 I is 0.01%. The 11 2 − isomer 123m Te is fed in 0.010±0.005% of the decays of 123 I. The levels of 123 Te are fitted considerably better by the recent predictions by Kisslinger and Kumar than by the older calculations of Kisslinger and Sorensen.

Decay of 19 min 67Ge to levels of 67Ga

Abstract The decay of 19 min 67 Ge to levels of 67 Ga has been studied with large Ge(Li) detectors and Ge(Li)-Ge(Li) coincidence experiments. A total of 56 γ-rays were observed and all but 8 have been placed in the decay scheme. Levels are observed in 67 Ga at 167, 359, 828, 911, 1082, (1203), (1556), 1640, 1810, 1976, 2527, 2620, 2731, 3162, 3225, 3402, 3632, 3655 and 3728 keV. The levels below 3600 keV have also been seen in one or more nuclear-reaction studies. We found no evidence for a level at 333 keV that was previously proposed to decay via a cascade of unresolved 166.5 keV γ-rays. Levels observed in odd-mass isotopes of Cu, Ga and As are discussed and compared with theoretical predictions.

Decay schemes of 70 min 129gTe and 33 d 129mTe

Abstract Gamma rays emitted in the decay of 70 min 129g Te and 33 d 129m Te have been investigated with Ge(Li) and NaI(Tl) detectors. Results of Ge(Li)-NaI(Tl) coincidence studies, coupled with relative intensity measurements for both isomers, suggest a decay scheme considerably different from those recently proposed by other workers. Excited levels are placed in 129 I at 27.7, 278.4, 487.4, 559.8, 696.0, 729.8, 829.8, 844.7, 1050, 1111.4, 1260, 1291, and 1402 keV. Beta decay of 129g Te feeds all of these except the ones at 696.0, 729.8, 768.9, 844.7, 1050 and 1402 keV. Beta transitions form 129m Te populate all of the latter set of levels and the ground state. The I.T. branching fraction of 129m Te is about 72%. With some exceptions the levels of 129 I agree rather well with those predicted by Kisslinger and Sorensen. Considerable evidence for the previously suggested hindrance of β-decay caused by phonon mixing of the wave functions has been observed.

Decay scheme of 3.9 d 127Sb

Abstract Beta and γ-rays emitted in the decay of 3.9 d 127 Sb have been studied with the use of Si(Li), Ge(Li) and NaI(Tl) detectors and coincidence equipment and the level scheme of 127 Te has been constructed. In order to check on interference from other antimony isotopes, sources were prepared by separating antimony directly from fission products, by milking antimony from separated tin fission products, and by use of the 128 Te(γ, p) 127 Sb reaction followed by chemical separation. A total of 33 γ-rays were observed, of which 32 were placed in the level scheme of 127 Te. Levels of 127 Te populated by decay of 127 Sb were observed at the following energies: 61, 88, 341, 473, 503, 631, 686, 764, 784, 786, 924, 1077, 1142, 1155, 1290, 1323 and 1378 keV. The properties of low-lying, even-parity levels of 127 Te are in reasonable agreement with the predictions of Kisslinger and Sorensen. Evidence for 9 2 − “intruder” state at 341 keV in 127 Te similar to that at 322 keV in 125 Te was found. Additional evidence for apparent hindrance of allowed β transitions was obtained.

Decay of 56 min 69gZn, 14 h 69mZn and 39 h 69Ge to levels of 69Ga

Abstract The decay of 69mZn was found to have weak β-branches to the 574 (0.032±0.005%) and 872 keV (0.004±0.002%) levels of 69Ga in addition to the prominent (>99.9%) 439 keV isometric transition to 69gZn. Decay of the latter includes a weak (0.0015±0.0005%) β-branch to the 318 keV level of 69Ga. Ten of the 36 γ-rays assigned to the decay of 69Ge in this work had not previously been observed. Levels are established in 69Ga at 318, 574, 872, 1106, 1336, 1487, 1525, 1723, 1891, 1923, 2022 and 2043 keV. The recent level predictions by Kisslinger and Kumar are in better agreement with the observed levels of 69Ga than previous calculations although discrepancies in levels positions are still rather large. As the energies of the excited states of even nuclei in the vicinity of 69Ga do not vary smoothly with N and Z, it is doubtful that a generalized type of calculation (e.g. Kisslinger-Kumar) can provide a very good fit to levels in the region. The log ft value of 8.6 for the β− transition from 1 2 − 69gZn to the 1 2 − level at 318 keV in 69Ga is among the largest known for allowed transitions. The half-lives of the species studied were determined to be 69gZn, 55.6±1.6 min; 69mZn, 14.4±0.1 h and 69Ge, 39.05±0.10 h. A value of 0.102±0.004 was obtained for the isomer-yield ratio 69mZn/69gZn in the 68Zn(n,γ)69Zn reaction.

Decay of 13.5 h 109gPd to levels of 109Ag

Abstract The β- and γ-decay of the 13.5 h 109gPd to levels of 109Ag has been studied with the use of Ge(Li) detectors, NaI(Tl) crystals and coincidence equipment. The energies (in keV) and relative intensities of γ-rays observed are: 45(3.6), 88(8900), 104(2.2), 135(3.2), 146(2.7), 311(100), 391(2.5), 413.5(26), 415.2(23), 425(1.8), 448(2.6), 551(1.5), 558(6.2), 602(21.5), 636(27), 647 (65), 702(9.2), 707(4.5), 737(5) and 782(33). Excited states in 109Ag were observed at 88 (41 sec 109Ag), 133, 311, 415.2, 702, 724, 736, 840, 863 and 870 keV. Spin and parity assignments for most of the levels were made on the bases of log ft values and γ-ray branching ratios along with data on Coulomb excitation from previous workers. The levels at 0, 311, 415.2, 702 and 863 keV have negative parity and have previously been observed in Coulomb excitation studies. The positive-parity levels at 133 keV has high spin and is apparently the g 9 2 single-quasi-particle level. The negative-parity levels of the odd-mass silver isotopes are understandable in terms of phonons coupled with the p 1 2 single-quasi-particle. However, properties of the positive-parity levels, particularly the low-lying 7 2 + level are not well explained by current nuclear models.

Decay of the 55 min and 12 min 133Te isomers

Abstract Gamma rays emitted in the decay of the 133 Te isomers, 55.4 min 133m Te and 12.5 min 133g Te, have been observed with Ge(Li) detectors. Sources were prepared by separating Sb from fission products, allowing several minutes for decay of 2.7 min 133 Sb and then separating the Te daughter activities. A total of 29 γ-rays between 312 and 2541 keV were attributed to decay of 133g Te and 30 from 74 to 2050 keV to that of 133m Te. Gamma-gamma coincidences in the decay of 133g Te were observed with a NaI(Tl) Ge(Li) set-up. The decay scheme of 133g Te was constructed, involving placement of 25 of the γ-rays emitted. The decay of 133g Te populates levels in 133 I at 0, 312, 720, 787, 1313, 1333, 1374, 1565, 1718, 2137, 2194 and 2541 keV. The decay of 133m Te is very complicated, and we have not attempted construction of a complete decay scheme for it; however, levels at 913 and 1561 keV in 133 I are definitely populated in 133m Te decay. The value for Q β of 133 Te was measured as 3.52±0.10 MeV. The low-lying levels of the odd-mass iodine isotopes vary smoothly through the series 125 I through 133 I. The levels of 133 I are fitted rather well by predictions based on quasi-particle-phonon coupling.

Decay schemes of 109 d 127mTe and 9.4 h 127gTe

Abstract Gamma rays emitted in the decay of a secular equilibrium mixture of 109 d 127m Te and 9.4h 127g Te and in the decay of 127g Te alone have been investigated using high-resolution Ge(Li) detectors. In the decay of the equilibrium mixture, five new γ-rays have been observed with energies: 172.1, 375.0, 618.6, 628.6 and 651.0 keV. New β-transitions observed in the decay of 127g Te are to levels at 375.0 keV and 618.6 keV, and a new transition to a 628.6 keV level is observed in 127m Te decay. Comparative β- and γ-ray counting of equilibrium 127 Te sources with a low-background, proportional counter and Ge(Li) detectors, respectively, established absolute values for β-group intensities to levels of 127 I. The I.T. branching of 127m Te was found to be 97.6 %, and the β-group intensity from 127g Te to the 127 I ground state is 98.8 %. The log ft values of 8.7, 9.7 and 8.7 for allowed β-transitions to the levels at 619, 375 and 203 keV, respectively, disclose severe hindrances that reflect dissimilarities in parent and daughter state wave functions. Hindered first-forbidden β-transitions were also observed.

Decay of 35 min 111Sn to levels of 111In

Abstract The EC/ β + and γ-decay of 35 min 111 Sn to levels of 111 In has been studied with Ge(Li) and NaI(Tl) detectors. A total of 16 γ-rays between 373 and 2325 keV are definitely assigned to the decay scheme. Excited states of 111 In are established at 536 ( 111m In), 1101, 1153, 1610, 1915, 2107, 2178, 2213 and 2325 keV. The isomer 7.3 min 111m In is produced in 0.09% of the 111 Sn decays. The spin-parity assignment of 111 Sn is 7 2 + and those of 111 In and 111m In are 9 2 + and 1 2 − , respectively. The EC transitions to all of the observed higher levels of 111 In, except possibly the one at 1543 keV are allowed, leading to assignments of 5 2 , 7 2 , or 9 2 + for those levels. We obtained no evidence for any transitions to 1 2 + or 3 2 + levels similar to those in 115 In and 117 In that have been suggested as the lowest members of a rotational band.