The decays of 5.5 min Lu and 6.7 min Lu

In order to clear up important discrepancies amongst previous investigations, the decay of ¹⁶⁸Lu, produced through the ¹⁶⁹Tm (α, 5n) reaction, has been re-investigated. Instead of the well-known 7 min activity, evidence has been obtained for two distinct decays with half-lives of 5.5 min and 6.7 min. The corresponding Q-values have been determined to be respectively 4470±80 keV and 4690±100 keV. The decay schemes are given for each isomeric state. The assignments 6⁻(p404↓+n523↓) and 3⁺(p541↓+n523↓) are proposed for ^168gLu (5.5 ruin) and ^168mLu (6.7 min), respectively. The structure of the levels are discussed in the framework of current nuclear models.     

Decay of the 55 min and 12 min Te isomers

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

The decay of 91 min As

The energies and relative intensities of γ-rays following the β-decay of ⁷⁸As (and ⁷⁶As) to levels in ⁷⁸Se (and ⁷⁶Se) have been measured using an 8 cm³ Ge(Li) spectrometer. The β-decay of ⁷⁸As has been measured using a superconducting magnet beta-ray spectrometer with two 3 mm thick Si(Li) detectors. These data plus β-γ and γ-γ coincidence results have been used to construct a level scheme with 18 excited levels in ⁷⁸Se. The half-life of ⁷⁸As was measured to be 90.7±0.2 min.     

The decay properties of 3.25 min 169Hf and 2.05 min 167Hf

The decays of 3.25 min ¹⁶⁹Hf and 2.05 min ¹⁶⁷Hf have been studied with high-resolution Ge(Li) and Si(Li) detectors. The total decay energy of ¹⁶⁹Hf determined from our experimental $\text{K}\text{β}{}^{\mathrm{+}}$ ratio is 3.29^+0.05_?0.13 MeV. The allowed unhindered character of the main β-branches in the decay of both isotopes allows unique Nilsson model assignments.     

The decay of 1.2 min Ag and 5.3 h Ag

The decay schemes of 1.2 min and 5.3 h ¹¹³Ag have been studied using Ge(Li) and NaI(Tl) detectors and a 4096-channel multiparameter pulse-height analyser system. The decay of 5.3 h ¹¹³Ag was found to involve 15 γ-rays and to produce 10 excited states in ¹¹³Cd at energies of 264.7, 298.0, 315.6, 583.9, 604.6, 681.1, 883.6, 936.9, 989.0 and 1195.2 keV. The italicized energies refer to negative parity states, through which 1.3% of the decays go to yield the isomer at 264.7 keV. The 604.6 keV level is thought to be a case|9/2⁻ level similar for those found in several odd-mass Te and Xe isotopes. The 1.2 min ^113mAg decay was found to populate several of the same levels in Cd and two additional levels at 452 and 689 keV. The 1.2 min ¹¹³Ag is the upper isomer with high spin, probably .     

The decay of 23.0 min Rb to levels in Kr

The radioactive decay of ⁷⁹Rb(23.0±0.5 min) has been studied with the aid of semiconductor radiation detectors. Both singles and coincidence spectra have been recorded. The decay energy: 3520±45 keV was determined by measuring the endpoint of the positon spectrum in coincidence with prominent γ-rays. A decay scheme is proposed incorporating most of the measured γ-rays. The following energies in keV and parities of levels are assigned: ground state ( ), , , , , 383.71±0.18, 532.82±0.33, 688.21±0.09, , 934.0±1.4, 1089.4±0.4, 1474.7±0.3. The spin and parity of the ⁷⁹Rb ground state is most probably .     

The decay of 4 min 158Tm

The decay of 4 min ¹⁵⁸Tm has been investigated with on-line mass-separated samples obtained from the Orsay ISOCELE separator. Measurements of γ-rays, conversion electron lines and γ-γ bi-dimensional coincidences were performed. About 180 transitions were ascribed to the decay and two thirds of them were placed in a decay scheme. The β-band and the γ-band were identified with bandheads situated at 806.40 and 820.13 keV respectively. In addition, a number of other vibrational bands (β-γ, β-β, K^π = 0^? and 1^?) are proposed. The decay properties of those bands are discussed in the framework of current nuclear models. The log ft values suggest a 2^? assignment for ¹⁵⁸Tm with the possible configuration (p404J↓-n521↑).     

Decay of 59.3 min 128Sn to levels of 128Sb

The γ-ray spectra associated with the decay of 59.3 min ¹²⁸Sn have been measured with Ge(Li) detectors. In order to recognize γ-rays of ¹²⁸Sn and ^128mSb, the decay and/or growth of γ-rays emitted from a tin sample separated chemically from fission products were measured. The decay of ¹²⁸Sn is followed by the intense Sb X-rays and 32.1, 45.8, 75.1, 80.9, 115.9, 152.6, 404.4, 482.3, 557.3 and 680.2 keV γ-rays. On the basis of the measured singles and γ-γ coincidence spectra and the analysis of intensities of true sum peaks, a new decay scheme has been constructed. The 10.0 min isomer in ¹²⁸Sb decays by β-emission (96.4%) to excited levels in ¹²⁸Te and by an isomeric transition (3.6 %) to the 9.1 h ground state.     

The decay of 159Tm (9.0 min) to 159Er

The decay of ¹⁵⁹Tm ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 9.0±0.4min}$) has been investigated with Ge(Li) andSi(Li) detectors, B-spectrographs and a toroidal spectrometer using isotopically separated samples produced by the YASNAPP facility at Dubna. The singles γ-ray spectrum, the conversion electron spectrum, the positron spectrum, prompt and delayed γ-γ coincidences were measured. Using strong thulium activities, conversion electrons were also measured with high resolution b-spectrographs. In the ¹⁵⁹Tm decay 81 new γ-ray transitions were observed. A decay scheme of ¹⁵⁹Tm is proposed involving 12 excited states in ¹⁵⁹Er. The first members of the rotational bands $\text{3}\text{2}$^?[521], $\text{5}\text{2}$^?[523], $\text{3}\text{2}$⁺[402 + 651], $\text{11}\text{2}$^?505 and $\text{7}\text{2}$^?[514] and the $\text{5}\text{2}$, $\text{7}\text{2}$ and $\text{9}\text{2}$ states of a strongly perturbed positive parity band were identified. The Q-value of ¹⁵⁹Tm was determined to be 3.4±0.3 MeV.     

Levels in 161Tm excited in the decay of 4.2 min 161Yb

The decay of ¹⁶¹Yb ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 4.2}\text{min}$) has been investigated with Ge(Li) and Si(Li) detectors and a toroidal β-spectrometer. Isobarically separated samples produced by the YASNAPP facility at Dubna Institute were used. The singles γ-ray spectrum, the conversion electron spectrum, γ-γ-τ and e-γ coincidences have been measured. In all, 67 γ-ray transitions have been observed. A decay scheme for ¹⁶¹Yb is proposed involving 12 excited states in ¹⁶¹Tm. The $\text{7}\text{2}$⁺[404], $\text{7}\text{2}$^?[523] and $\text{5}\text{2}$⁺[402] levels have been identified. The interpretation of the high-lying levels is discussed. The Q-value of ¹⁶¹Yb decay has been determined to be 3850 ± 250 keV. The A-dependence of the energies of the one-quasiparticle states in odd-A Tm isotopes is demonstrated.     

The decays of 21.55 min 162gTm and 24.3 s 162Tm (a new isomer)

The decay of the 21.55 min ground state and of the 24.3 s isomeric state of ¹⁶²Tm was investigated with semiconductor detectors. The γ-ray spectrum was investigated with a Compton-suppression Ge(Li)-NaI(Tl) arrangement. A Si (Li) detector, mounted in an electron transport solenoid, was used to investigate the conversion electron spectrum. Three-dimensional coincidence measurements were performed with large-volume Ge(Li) detectors. The ¹⁶²Tm ground state has spin-parity 1^? and Nilsson assignment p[411]↓?n[521]↑. An allowed β-transition (log ft ≈ 6.4) was observed to a 2^?, 2 octupole vibrational level at 1572.84 keV. The Q-value determined from positon-gamma coincidence measurements is 4705 ± 70keV. The discrepancy of the experimental K /β⁺ ratio with theoretical predictions might possibly be explained by a large number of unobserved weak γ-rays besides the total of 315 stronger ones observed in this study. The average β-strength function was calculated to be 1.2 × 10^?5. Among the 50 levels observed in the decay, the 2⁺, 4⁺ and 6⁺ members of the ground-state band, the 2⁺, 3⁺ and 4⁺ members of the γ-band, several 0⁺ and 2⁺ members of the K = 0 β-bands and 1^?, 2^? and 3^? octupole vibrational levels were identified. Parameter values Z_γ(0) and Z_γ(2) determining the mixing between the γ-band and the ground-state band, allow no conclusive evidence about unequalness of the intrinsic quadrupole moments of the ground states and the γ-band. The Z(0) parameters, determining the mixing between the β-bands and the ground-state band, and X parameters determining the ratio of E0 to E2 transition probabilities, were deduced. A previously unreported 24.3 sec isomer in ¹⁶²Tm was observed to decay in 10% of the cases by an allowed unhindered (log ft = 4.7) β-ray transition to a level at 1712.20 keV in ¹⁶²Er. The Nilsson configurations assigned to the isomeric and 1712.20 keV levels are p[523]↑ + n[521]↑₅₊ and n[523]↓ + n[521]↑₄₊ respectively. The isomeric level decays in 90% of the cases by an E3 transition (E_IT < 125 keV) to a p[404]↓ ?n[521]↑_2? level at 66.90 keV in ¹⁶²Tm, which decays by an (M1+ < 40 % E2) to the 21.55 min ¹⁶²Tm 1^? ground state.     

Delayed-neutron emission from short-lived Br and I isotopes

Rapid radiochemical separation techniques have been used to investigate the delayed-neutron emission from bromine and iodine isotopes produced by thermal-neutron induced fission of ²³⁵U. The nuclides 0.63 sec ⁹¹Br, 0.26 sec ⁹²Br and 0.41 sec ¹⁴¹I have been identified as delayed-neutron precursors. Relative neutron abundances of these and of the known precursors ^87–90Br and ^137–140I have been measured and absolute neutron abundances and neutron emission probabilities have been deduced. The P_n values are discussed within a simple semiempirical picture.     

Identification of the nuclide 226U

Identification of the uranium isotope ²²⁶U is reported. This nuclide was produced in bombardments of ²³²Th with 140 MeV ⁴He ions. It is observed to decay by α-particle emission with a half-life of 0.5±0.2 sec and has an α-particle energy of E_α = 7.43±0.03 MeV, giving a Q-value of Q_α = 7.56±0.03 MeV. Detection was achieved by on-line counting and pulsed-cyclotron beam techniques. It is also observed that the maximum yields for (α, p(x ? 1 )n) reactions are about ten times greater than those for (α, xn) reactions at these energies.     

Comparison of the spontaneous fission of 244Cm and 252Cf: (I). Fragment masses and kinetic energies

The energy of both fission fragments of ²⁴⁴Cm and ²⁵²Cf, respectively, was measured in coincidence with the prompt neutrons (see part II). Energy calibration of the surface-barrier detectors was done after the method of Schmitt et al. with the ²⁵²Cf fragments. Mean values and rms widths of the mass and energy distributions of both isotopes are calculated and compared with the results of other authors. The total kinetic energy of ²⁴⁴Cm fragments is at least as high as that of ²⁵²Cf fragments.     

Energy spectra of delayed neutrons from separated fission products: (III). The precursors 88Br, 90Br, 138I, 140I, 142(Xe+Cs) and 144Cs

Energy spectra of delayed neutrons from the mass-separated fission products ^{88. 90}Br, ^{138, 14}I, ¹⁴²(Xe+Cs) and ¹⁴⁴Cs have been measured. Average level spacings, neutron envelopes and P_n values were calculated and compared with the experimental data. The neutron envelopes are well reproduced for all precursors except ⁹⁰Br and ¹⁴⁰I. For the latter the neutron window predicted by various mass formulae is too wide and a considerable reduction was found necessary to bring calculated envelopes in agreement with the experimental distributions.     

Level structure of the 89-neutron nucleus 153Gd: (I). Levels and gamma-transitions in 153Gd excited in the decay of 153Tb

Investigations of the properties of ¹⁵³Gd excited states populated in ¹⁵³Tb decay were continued. The following measurements were performed: coincidence spectra e^?γ with L41, K93 + L52, K110, K129 + L87 + L88 and K195 + L152 keV conversion electron lines, angular correlations of high energy γ-cascades going through the 109.7 keV level, delayed e^?γ and e^?e^? coincidence spectra to determine the half-lives of 41.5, 93.3, 109.7, 129.1,183.5, 212.0 and 216.1 keV states, R(135°, ± B) parameters of IPAC for the 102–110 and 83–129 keV cascades using ¹⁵³Tb sources implanted into Fe foil.A decay scheme of ¹⁵³Tb containing 50 excited levels is proposed. Their spins, parities, $\text{log}\text{?t}$ and, for low-lying levels, also the mean half-lives have been determined. An estimation of the g-factors of the 109.7 and 129.1 keV levels has been given. On the basis of half-lives of investigated states absolute values of reduced γ-transition probabilities for these states have been calculated. The structure of the ground state of ¹⁵³Gd is discussed.     

Decay of Cd and levels of Ag

The γ-ray spectrum following the decay of ¹⁰⁴Cd has been investigated with Ge(Li) spectrometers. Two unreported γ-rays with energies of 625.2 and 709.2 keV were observed and placed in the proposed decay scheme.     

The decay schemes of Y and Y and γ-rays observed in the decay of Y

Active yttrium was separated from ²³⁵U fission products and the decay of ⁹⁴Y, ⁹⁵Y and ⁹⁶Y to the levels of ⁹⁴Zr, ⁹⁵Zr and ⁹⁶Zr, respectively, has been studied with the aid of a 17 cm³ Ge(Li) detector. Gamma-ray energies and intensities were accurately determined. In the decay of ⁹⁴Y four new transitions at 1232.78 ± 0.35, 1324.97 ± 0.35, 1363.48 ± 0.35 and 2467.00 ± 2.75 keV were observed. The data obtained support the level scheme proposed for ⁹⁴Zr by Knight et al. and that deduced from more recent reaction data. Evidence supporting the location of the 0⁺ excited state at 1300 keV is presented. Branching ratios are calculated and a modified level scheme for ⁹⁴Zr is proposed. In the decay of ⁹⁵Y the energies of 13 γ-rays, previously identified with the decay of this nuclide, have been accurately measured and are presented in a partial level scheme for ⁹⁵Zr. The data obtained in this work support the level structure deduced from reaction data by Cohen and Chubinsky and by other workers. New γ-transitions at 550.10 ± 0.23, 1723.30 ± 0.90 and 1805.0 ± 1.0 keV were measured in the decay of ⁹⁶Y.     

The decay of Sc and V

The decays of ⁴⁸Sc and ⁴⁸V have been studied with Ge(Li) diodes, scintillation spectrometers and a double focussing beta-ray spectrometer. The 3507 keV level, from which originates the quadruple cascade (9.4±0.5)% in the ⁴⁸Sc decay, is also de-excited by a 1212 keV cross-over transition to the 2295 keV (4⁺) level and supports the assumption, that the 3507 keV level has a spin 6⁺. The first member of the reported triple cascade in the ⁴⁸V decay is shown to be a doublet of 928.9±0.7 (1.2±0.2)% and 944.3±0.5 keV (8.0±0.5)% gamma rays, both followed by the 1311.4–983.3 keV cascade. Evidence was found, that the 2421 keV (2⁺) level is excited by weak gamma rays from high-energy levels. The K/β⁺ ration in the ⁴⁸V decay is 0.69±0.05 The Q-values of ⁴⁸Sc and ⁴⁸V are calculated to be 3986±7 keV and if 4015±4 keV, respectively. The energy of the gamma ray of ⁴⁷Sc, which is present as an impurity, is 159.2±0.5 keV.