H.-U. Siebert

The decay scheme of 127Ba and half-lives of some low-lying excited states in 123, 125, 127, 129Cs

Abstract Radioactive sources of 123, 125, 127, 129 Ba obtained in the spallation reaction have been studied with Ge(Li), Si(Li), NaI(Tl) and plastic detectors. On the basis of γ-ray energies, intensities, energy sums and coincidence information, the decay scheme has been proposed for 127 Ba. No high-spin isomer of 127 Ba has been observed. The lifetimes of 5 2 + → 1 2 + transitions in 123, 125, 127, 129 Cs have been measured. No evidence for the shape isomerism in 127 Cs has been found.

Excited states of the doubly odd deformed nucleus 160Tm

Abstract The decay of 4.8 min 160 Yb has been investigated by means of Ge(Li) detectors, toroidal and magnetic-lens β-spectrometers and scintillation counters. The singles spectra of γ-rays and conversion electrons as well as prompt and delayed γ-γ and γ-ce coincidences have been measured. The 160 Tm level scheme is proposed including 94.5% of the total γ-ray intensity observed in the 160 Yb decay. The lifetimes of the 42.02, 174.40 and 215.78 keV states have been determined to be 1.6±0.3, 17±1 and 0.65±0.15 ns, respectively. From the analysis of the experimental data, the quantum characteristics of 160 Tm levels are proposed. Experimental γ-ray transition probabilities are compared with Weisskopf and Nilsson estimates, the latter also taking into account pairing correlations.

Levels in 163Tm excited by the decay of 11.4 min 163Yb

Abstract The decay of 163 Yb (T 1 2 = 11.4 min ) has been investigated with Ge(Li),Si(Li) and NaI(Tl) detectors, a toroidal β-spectrometer and magnetic β-spectrographs by using isobarically separated samples produced by the YASNAPP facility at Dubna. The singles γ-ray spectrum, the conversion electron spectrum, prompt and delayed γ-γ coincidences and β + - γ coincidences have been measured. In all, 110 new γ-ray transitions have been observed. A decay scheme for 163 Yb is proposed involving thirty excited states in 163 Tm. The first members of the rotational bands 1 2 + [411], 7 2 + [404], 1 2 − [541], 3 2 + [411] and 7 2 − [523] have been identified. Possibilities of interpretation for the high-lying levels are discussed. The Q -value of 163 Yb has been determined to be 3370±100 keV.

The decay chain162Yb (19·0 min) →162Tm (21·8 min) →162Er and the decay of160Tm (9·2 min) TO160Er

The decay of162Yb,162Tm and160Tm has been investigated with Ge(Li) and Si(Li) detectors using isotopically separated samples produced by the YASNAPP facility at Dubna. The singles γ-ray spectrum, β-γ and γ-γ coincidences were measured. Strong ytterbium and thulium activities were used for conversion electron measurements with high resolution magnetic β-spectrographs. 3, 134 and 39 new γ-rays were attributed to the decays of162Yb,162Tm and160Tm, respectively. Decay schemes of these isotopes are proposed. Three and 12 new levels were found in162Er and160Er, respectively. TheQ-values of162Yb,162Tm and160Tm were determined to be ≦2·2, MeV, 4·6±0·3 MeV and 4·9±0·5 MeV, respectively.

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

The decay of 159Tm (T12 = 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 32−[521], 52−[523], 32+[402 + 651], 112−505 and 72−[514] and the 52, 72 and 92 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 in165Tm excited by the decay of 9·8 min165Yb

The decay of165Yb (T1/2=9·8 min) has been investigated with Ge(Li), Si(Li) and NaI(Tl) detectors, a toroidal Β-spectrometer and magnetic Β-spectrographs. The isobarically separated samples produced by the YASNAPP facility at the Dubna Institute were used. The single γ-ray spectrum, the conversion electron spectrum, prompt and delayed γ-γ coincidences have been measured. The decay scheme of165Yb involving 40 excited states in165Tm has been proposed. The first members of the rotational bands l/2+[411], 3/2+[411], 5/2+[402], 7/2+[404], 1/2−[541], 7/2−[523] and 9/2−[514] have been identified.