C. Foin

New insight in the level structure of 153Er

Abstract: The high-spin level structure of the 153Er nucleus has been reinvestigated by in-beam γ-ray and electron spectroscopy with (14N,pxn) reaction. Excitation energies, spin and parity assignments are unambiguously established for the two lowest isomers T1/2≃ 380 ns and T1/2\simeq 10 ns. The characteristics of the third one (T1/2≃ 250 ns) at 5.2 MeV are still questionable but its main decay modes are better known. An extension of the level scheme is proposed up to 8.4 MeV.Experimental results have been discussed in terms of shell model multiplets and compared with the other structures observed in N=85 neighbouring nuclei.

On the nature of the 17 μs isomer of the 133Sb valence nucleus

Abstract: The decay of the 17 μs isomer of 133Sb was re-investigated experimentally. It was produced by thermal neutron induced fission of 241Pu. Its detection is based on time correlation between fission fragments selected by the LOHENGRIN spectrometer at ILL (Grenoble), and the γ-rays, and conversion electrons from the isomer. The interpretation of the level scheme is based on shell model calculations, where empirical two-body matrix elements were employed. The good agreement between theory and experiment suggests that the isomer is the 21/2+ member of the 2p-1h πg7/2ν(f7/2h11/2−1) configuration.

High spin states in the transitional odd-odd nuclei150Eu and152Tb

The (7Li, 5n) and (11B, 5n) reactions have been used to study the high-spin states in the two odd-odd nuclei150Eu and152Tb. Three decoupled bands have been evidenced in each nucleus belonging to the same configurations [f7/2]n [h11/2]p, [h9/2]n [h11/2]p and [i13/2]n [h11/2]p. The latter one is well developped and improves our knowledge of this system between the spherical and deformed region. The analysis of the collective moment of inertia and transition ratios strongly suggests an increase of the deformation when the rotational frequency increases in these two transitional nuclei150Eu and152Tb.

On the level scheme of the159Tm nucleus

Level in159Tm have been excited in the150Sm(14N,5n reaction. The yrast band 7/2−[523] observed up to spin 45/2− is built on a isomeric state at 166 keV (T1/2=37±5ns). Connections between the 7/2−[523] and 7/2+ [404] bands fix the band-head energies.

On-line γ-ray investigation of the14N+27Al reaction at 30 MeV/u

The cross-sections of target-like residues following the14N+27Al reaction at 30 MeV/u have been measured from in-beam and radioactiveγ-ray spectra. The recoil velocities of some fragments have been estimated from theγ-ray Doppler broadening.

High-spin yrast isomer in theN=83151Er nucleus

An highspin yrast isomer (T1/2 ∓ 420ns, E>10.286 MeV, 67/2≤ I≤ 71/2) is observed in the151Er nucleus excited in the116 Sn+40 Ca reaction, using the recoil shadow method.

Four quasi-particle band in the odd-odd158TM nucleus

The125Te (37CI,4n) reaction has been used to study the high spin states of158Tm by means of in beam gamma ray spectroscopy using Compton suppressed germanium detectors of the “Château de Cristal” facility. Besides the Yrast band, the rotational character of which is clearly established up to the 23− level only, a new rotational band developed up to spin 33+ is also observed. It is interpreted as a 4QP band.

Yrast and side bands in the odd-odd160, 162Tm nuclei

Abstract160, 162Tm nuclei have been reinvestigated at high spins by128, 130Te(37Cl, 5n) reactions, respectively. In the yrast bands of both nuclei the crossing frequencies correspond to the second neutron backbending (BC). The same is true for the side bands in162Tm but not in160Tm where the first neutron backbending(AB) is observed.