W. Trautmann

Yrast isomers and very high spin states in 148, 149, 151, 152Dy and 147Gd

Abstract We have studied level schemes for the feeding and decay of high-spin isomers in the nuclei 148, 149, 151, 152 Dy and 147 Gd. A variety of techniques involving γ-ray spectroscopy with pulsed heavy-ion beams have been applied including linear polarization, γ-γ correlations and recoil distance measurements. The general aspect of these level schemes is in accordance with the idea that the states near and along the yrast line can be described by a spheroidal shell model in which the nucleus is axially symmetric with respect to the total spin. In these cases the spin is generated not by collective rotation, but by alignment of many single-particle orbits around a common axis.

Single particle nature of the yrast line at high angular momentum in 152Dy

Abstract Linear polarization and Doppler shift recoil-distance decay curves for γ-ray transitions deexciting very high spin yrast states up to spin 36ħ in 152 Dy were measured with a delayed-promt γ-γ coincidence technique via the reactions 122 Sn ( 34 S, 4n) and 124 Sn( 32 S, 4n), at 150 MeV incident beam energy. The deduced experimental transition probabilities are consistent with those obtained for non-rotational nuclei indicating that the yrast angular momentum originates mainly from the alignment of individual particle spins.

Measurement of the linear polarization of continuum gamma rays from (32S, xn) reactions to prolate and oblate rare-earth nuclei

Abstract We describe the techniques and report the results of a measurement of the linear polarization, Pγ of continuum γ-rays from Er and Dy nuclei produced in (32S, xn) reactions on 130Te and 124Sn targets. For the prolate 156–158Er isotopes we find Pγ ≈ 0.35 in the γ-ray energy range if0.3 MeV ≦ Eγ ≦ 1.5 MeV, thus confirming the E2 nature of the unresolved yrast cascades in rotational nuclei. In contrast, the rather small polarization Pγ ≈ 0.05 for Eγ ≦ 1.0 MeV measured for the oblate 151,152Dy isotopes, and the shape of the spectrum of continuum γ-rays suggest a rather direct feeding of the yrast states by statistical cascades. For 1.0 MeV ≦ Eγ ≦ 1.5 MeV we find Pγ ≈ 0.3 indicating collective rotations of the Dy nuclei at spin I ≧ 40 h z.shtsls; . Measurements of γ-ray angular distributions with a collimated NaI detector support these results. From the reduction of the Pγ, and A2 values of the γ-ray continuum in 156–158Er, compared to those measured for discrete E2 yrast transitions, we obtain estimates for the intensities of the M1 and statistical components in the continuum of these nuclei.