M. Honusek

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.

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.

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

Abstract The decay of 161 Yb ( T 1 2 = 4.2 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 161 Yb is proposed involving 12 excited states in 161 Tm. The 7 2 + [404], 7 2 − [523] and 5 2 + [402] levels have been identified. The interpretation of the high-lying levels is discussed. The Q -value of 161 Yb 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.

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.

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.