T.A. Islamov

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.

166Er levels populated in the166Tm decay

The decay of166Tm has been investigated with samples obtained by chemical extraction and mass-separation from spallation products of tantalum irradiated with 660 MeV protons. Measurements of gamma rays, γ-γ bi-dimensional coincidences, CE-γ coincidences and internal conversion electrons have been performed. About 300 γ-transitions have been observed; most of them are placed in a level scheme of166Er. The properties of some rotational and vibrational bands and of some other levels are discussed.

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.

Study of167 Yb levels excited in the decay of167Lu

The167Lu source was isolated from products of spallation reaction induced by 660 MeV protons on tantalum target. The direct and the prompt coincidence spectra of gamma rays from the167Lu decay have been studied with different Ge(Li) detectors. Half-lives of several excited states in167Yb have been measured using the delayed coincidence technique. The internal conversion spectra were investigated with Si(Li) detector and with permanent magnet spectrograph as well. The energies and intensities of more than 400 gamma-transitions were determined. The multipolarities of 225 gamma-transitions were established. The proposed decay scheme of the167Lu is based on coincidence measurements, the analysis of energy sums and reaction data. The states in167Yb are interpreted in terms of the unified model. The role of the Coriolis coupling is discussed.