G. Lhersonneau

Structure of the highly deformed nucleus101Sr63 and evidence for identical K=3/2 bands

The low-energy level scheme of theN=63 nucleus101Sr has been obtained from a β-decay study of101Rb. The ν[532]5/2 and ν[411]3/2 orbitals are well established as the ground state and a band head at 271.2keV, respectively. The general properties of the level scheme indicate a quadrupole deformation ofβ ≃ 0.4, confirming the unique feature of saturation of deformation inN ≥ 60 Sr isotopes. The energies of theK=3/2 intraband transitions in the odd-neutron neighbours99Sr61 and101Sr63 are very similar. More generally, the identical bands at low spin in98–101Sr nuclei are correlated with the mass-independent moments of inertia in this region.

Lifetime measurements in99Sr and100Zr

The lifetime of the first excited state in99Sr has been determined by the delayed γ-γ coincidence method. The value of t/2=0.58(9) ns corresponds to a deformation parameter ß=0.38(4). The deduced value confirms the previously proposed ν[411]3/2 Nilsson assignment for the99Sr ground state. In addition, lifetime values for the 2+ (t1/2=0.40(8) ns) and 0+ (t1/2=5.36(23) ns) states in100Zr are obtained, which deviate from older measurements and indicate a larger deformation of ß=0.39(4).

Shape coexistence in theN=59 isotone97Sr

Experimental evidence for shape coexistence in the N=59 isotone97Sr is presented. The ground state and the lowest excited levels are confirmed to be spherical. At 585.1 keV, a K=3/2 rotational band built on the v[422 3/2] Nilsson configuration has been identified. Nilsson orbital assignments for three further levels of deformed origin are proposed. The results are compared to RPA shell-model predictions.

A new high-spin isomer in 39 97 Y58

An isomeric state at 3,523 keV excitation energy in97Y with a half-life of 144(10) ms has been discovered with the fission-product separator JOSEF. This isomer is depopulated through aγ transition of 162 keV. AnE3 multipolarity for this transition is consistent with the measured conversion coefficients ofαK=0.98(20) andαT=1.00(19). Subsequent electromagnetic transitions populate several new97Y levels which have high spins. For the isomer the three-quasiparticle configuration [πg9/2⊗ν(h11/2,g7/2)]27/2− is proposed. TheE3 transition with a strength about 2 single-particle units is supposed to be of the typeh112/+1→d52/−1. These findings provide evidence for the rapid shape transition atA≃100 since they indicate shell-model character of3997Y58 even at high excitation energies while the immediate neighbour3998Y59 contains a rotational band based on a level at 495 keV.

First decay study of the very neutron-rich isotope 93 Br

The decay of the mass-separated, very neutron-rich isotope

Saturation of deformation atN=60 in the Sr isotopes

{}^{93}mathrm{Br}

IBFFM predictions for low-lying spherical states in the shape-coexisting odd-odd nucleus98Y

has been studied by ensuremath{gamma} spectroscopy. A level scheme of its daughter

Nuclear structure of97Y in the interacting boson-fermion model

{}^{93}mathrm{Kr}

K-isomeric state in even-even100Sr

has been constructed. Level energies, ensuremath{gamma}-ray branching ratios, and multipolarities suggest spins and parities which are in accord with a smooth systematics of the

Structure of theN=59 nucleus97Sr: coexistence of spherical and deformed states

N=57