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.     

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.     

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 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↑).     

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.     

The decays of 121g,mCd to 121In

The decay of isotope-separated activities of ¹²¹Cd produced in fission have been studied by γ-ray and conversion-electron spectroscopy. A level scheme of ¹²¹In has been constructed. Transition probabilities between some levels have been deduced from a lifetime measurement. The experimental results are compared to a recent theoretical study of ¹²¹In.     

The half-life of 207Bi and decays of 211At and 211Po

The half-life of ²⁰⁷Bi was obtained from the genetic relation between ²⁰⁷Po and ²⁰⁷Bi, and between ²¹¹At and ²⁰⁷Bi. The half-life was found to be 33.4 ± 0.8 y. The half-life of ²⁰⁷Po was determined to be 5.81 ± 0.04 h by following the decay of the characteristic γ-rays from ²⁰⁷Po. The half-life of ²¹¹ At was determined tobe 7.23 ± 0.02 h by following the decay of γ-rays and α-particles from ²¹¹At and ²¹¹Po. The half-lives determined in the present work for ²⁰⁷Po and ²¹¹At agree with the literature although the half-life of ²⁰⁷Bi differs considerably from the currently accepted value of 38 y. The branching ratio of ²¹¹ At decaying through EC and α-decay modes was determined together with the branching ratios of the three α-particles emitted from ²¹¹Po.     

Positron decays of 25Al, 37K, 38K and 39Ca

Allowed β⁺ decay branches from ²⁵AI, ³⁷K, ³⁸K and ³⁹Ca have been sought by observation of delayed γ-radiation. The precision of previously known branches has been increased and improved limits obtained for unobserved branches.     

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.     

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.     

Beta decays of 25Na, 25Al and 29Al

The radioactivities ²⁵Na, ²⁵Al, and ²⁹Al were produced in the ²³Na(t, p)²⁵Na, ²⁴Mg(d, n)²⁵Al, and ²⁷Al(t, p)²⁹Al reactions using a 3.5 MV Van de Graaff. γ-radiations were measured by means of a target-transfer system and a Ge(Li) detector with or without Compton suppression. Decay schemes derived for ²⁵Na and ²⁹Al are in general agreement with earlier results, but with improved accuracy of branching ratios and much sharper limits on the intensities of certain unobserved β- and γ-ray transitions. Precision measurements of the energies of principal γ-rays gave results in keV for the listed decaying bodies as follows: ²⁵Na ? 1611.716(11); ²⁵Al ? 1611.708(11); and ²⁹Al ? 1273.361(9). The energy determinations of the ²⁵Mg 1612 keV γ-transition measured in the decays of ²⁵Na and ²⁵Al differ by 8 ± 9 eV.     

Investigation of parity mixing in Ta and Lu by measurement of the circular polarization of γ-rays

The circular polarization of the 482 keV γ-radiation of ¹⁸¹Ta and the 343 keV γ-radiation of ¹⁷⁵Lu was measured with a Compton polarimeter. Spurious effects arising from higher order contributions of quantum electrodynamics to the Compton scattering cross section were discovered. The results for the polarization are P = − (4.1±1.3)10⁻⁶ for ¹⁸¹Ta and P = − (1.5±6.0)10⁻⁶ for ¹⁷⁵Lu. These values are corrected for instrument asymmetries, bremsstrahlung and intensity of other lines.     

Levels of 190Os populated in the decays of 3.3 h 190mRe and 12 d 190Ir and in the 189Os(d,p)190Os reaction

The level structure of ¹⁹⁰Os has been investigated by the techniques of radioactive decay and neutron transfer reaction spectroscopy. The existence of 3.3 h ^190mRe has been confirmed; it decays ≈ 49% by isomeric transitions and ≈ 51% by β^? decay to levels in ¹⁹⁰Os with spins $\text{\$}\text{?}\text{= 5}$. In a re-investigation of the 12 d ¹⁹⁰Ir decay, a virtually complete decay scheme has been established and discrepancies between the I^π values assigned to several ¹⁹⁰Os levels by earlier workers have been resolved. The reaction ¹⁸⁹Os(d, p)¹⁹⁰Os has been studied and information about the locations of two-quasiparticle states involving the $\text{3}\text{2}\text{[512]ν}$ orbital and about the microscopic compositions of collective excitations has been derived. Various aspects of the ¹⁹⁰Os level structure are discussed in the light of the combined radioactivity and transfer reaction results.     

The decays of the Tz = 32 β-delayed proton precursors 83Zr, 87Mo and 91mRu

The decays of the nuclides ⁸³Zr,⁸⁷Mo and ^91mRu have been studied with singles proton counting as well as with pX and pγ coincidences. The half-lives for the three nuclides were measured to be 37.8 ± 1.1 s, 13.3 ± 0.4 s and 7.6 ± 0.8 s, respectively. The proton branch in the decay of ⁸³Zr that populates the first excited state in ⁸²Sr was measured to be (6 ± 4) % of the total delayed proton decay. The corresponding branch in the decay of ⁸⁷Mo, populating the first excited state in ⁸⁶Zr was measured to be (15 ± 8) %. Restrictions to the possible spin and parity assignments of ⁸³Zr and ⁸⁷Mo were deduced from comparisons between the experimental excited-state branches, and those predicted from a statistical model of delayed particle decay. Fits to the endpoints of the delayed proton spectra from ⁸³Zr and ⁸⁷Mo yielded values of the energy available for delayed proton decay (Q_e.c.?B_p) of 2.75 ± 0.10 MeV and 3.7 ± 0.3 MeV, respectively. Comparison between calculated and experimental proton spectra was used as an argument that the source of ⁹¹Ru activity is actually a $\text{1}\text{2}{}^{\mathrm{?}}$ isomer.     

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.