M. Lach

Multiparticle- and particle x octupole states in 65 149 Tb84

Yrast- and above-yrast states in149Tb were investigated in (α, 6n) and (7Li, 2n) in-beamγ-ray experiments. The yrastγ-ray cascade strongly populates three-valenceparticle states involving theh11/2 proton and thef7/2,h9/2, or;i13/2 neutron orbitals, as well as the high-spin levels formed by the couplings of the three149Tb valence particles, to the low-lying146Gd octupole phonon and to higher-lying proton particle-hole core excitations. The data give the (πh11/2vi13/2)12− attraction free of octupole contributions as -631 keV. The shell model with empirical two-particle- and particle-phonon residual interactions gives an excellent quantitative description of the149Tb energy levels. It is noted that the observed highspin members of theπh11/2vh9/2vf7/2 configuration closely resemble the lowest symmetric and mixed-symmetry representations of theS3 permutation group.

The 10+ states ofνh 11 2/−2 and πh 11 2/2 character in theN=80 isotones144Gd and142Sm

In-beam studies with (α,4n) and (3He, 3n) reactions have located a second 10+ state closely above the 10+ isomers in144Gd and142Sm. The data characterize the142Sm 10+ isomer as the νh112/−2 excitation in contrast to144Gd where the 10+ isomer is of πh112/2 character.

Shell model yrast states in theN=79 nuclei141Sm and143Gd

In (α,5n) in-beam γ- and electron measurements we have established high-spin states in the 3-neutronhole nuclei141Sm and143Gd. Observed energy levels below 4 MeV are interpreted in terms of shell model configurations where the odd h11/2 neutron hole couples to the N=80 core excitations containing one h11/2 proton particle or one h11/2 neutron hole. Higher-lying yrast states are built on a 23/2− level at Rd 3.2 MeV probably involving the πh12/2guh112/−1 configUTa-tion.

Collective high spin states in 45Sc

Abstract The high-spin states in 45 Sc were studied with the GASP multidetector array. The nuclei were excited by the 30 Si( 18 O,p2n) 45 Sc reaction at E LAB =60 MeV and separated with the Recoil Mass Spectrometer. Several new high-spin levels extending the known single-particle and collective structures were observed. Energies of the negative-parity states agree with the shell model predictions whereas the positive-parity-intruder rotational band extends up to very high rotational frequencies and continues beyond the maximum angular momentum available from the single-particle f 7 2 configuration.

Three-nucleon yrast states in145Sm

In-beamγ-ray and conversion electron measurements with (α, xn) reactions have established the145Sm highspin states up toIπ=25/2+ at 3.5 MeV excitation. A shell model analysis using empirical two- and one-body energies from neighbouring nuclei classifies the low-lying odd-parity levels as 3-quasiparticle states formed by the144Sm two-proton-hole excitations and thef7/2 valence neutron. The higher-lying positive-parity states involve particle-hole core excitations with one proton inh11/2.

In-beam study of 63 143 Eu80

An in-beam γ-ray study with the144Sm (α, p4n) reaction has established the high-spin states up to 5 MeV excitation and I=35/2 in the N=80 nucleus143Eu. The observed yrast states show the typical irregular pattern of a spherical nucleus, with frequent decay branchings and often dominant dipole de-excitation. The level spectrum is in qualitative accord with the coupling of the h11/2 proton particle to the known yrast levels of the142Sm core nucleus. Only in a few cases specific configuration assignments are made.

First observation of yrastγ-rays in theN=78 nuclei142Gd and141Eu

Excitation function measurements with α-particles and HI-beams clearly attribute the yrast cascade previously proposed for142Gd to the141Eu neighbouring nucleus. The so far unknown yrast transitions of142Gd have been identified. Coincidence measurements establish the high-spin level schemes of the two nuclei up to 3.2 MeV.

Proton- and neutron H11/2 excitations in 63 141 Eu78

An (α,p6n) in-beam γ-ray experiment has established the high-spin states of the N=78 nucleus141Eu up to I=35/2− at 4.4 MeV excitation. The levels above 3 MeV involve the couplings of the h11/2 valence proton to either two aligned h11/2 proton particles or two aligned h11/2 neutron holes. The observed spin sequences are in accord with the shell model for these couplings.