C. Baktash

Quadrupole collectivity and shapes of OsPt nuclei

Abstract E2 collective properties for the low-lying states in 186,188,190,192 Os and 194 Pt have been investigated experimentally by means of Coulomb excitation using 3.3–4.8 MeV/nucleon 40 Ca, 58 Ni, 136 Xe and 208 Pb beams. The deexcitation γ rays following Coulomb excitation were detected in coincidence with the scattered particles. Levels with excitation energies up to 3–4 MeV of the ground-state, γ and 4 + collective bands as well as excited 0 + states were populated in each nucleus studied. A semiclassical Coulomb-excitation least-squares search code GOSIA was used to extract E2 matrix elements from the measured γ-ray yields. For each nucleus studied, a unique and almost complete set of E2 matrix elements for the low-lying states has been determined, which includes both the magnitudes and signs of the transitional and diagonal matrix elements. The completeness of the set of measured E2 matrix elements makes it possible to determine the intrinsic quadrupole deformation for the low-lying states in these nuclei via a model-independent method. The results indicate clearly that the E2 properties for the low-lying states in these nuclei are correlated well using only the quadrupole collective degrees of freedom. The extracted E2 matrix elements are compared with the prediction of various collective models such as the asymmetric rigid rotor model, the γ-soft model of Leander, and the IBA-2 model. These particular models do not reproduce the data satisfactorily, however the general trends of the data are consistent with the descriptions of γ-soft type collective models through a prolate to oblate shape-transition region. That the enhanced B (E2) values between the I ,quasi- K π = 4,4 + state and members of the I ,quasi- K π = 2,2 + band are well reproduced by the γ-soft model is consistent with the interpretation of the I ,quasi- K π = 4,4 + state being a two-phonon γ-vibration excitation.

The high-spin structure of 100Rh☆

Abstract High-spin states of 100Rh have been populated with the reactions 99Ru(α, 2np) and 98Mo(6Li, 4n) and their γ-decay has been studied with Ge(Li) detectors in singles and coincidence. Angular and time distributions of the γ-rays were also measured. As a result 14 new levels spanning spins up to I = 16 built on the 5+, 4.5 min isomer at 107 keV have been established, and a half-life of T 1 2 = 120 ± 5 nsec has been determined for the 7+ state at 111.9 keV. The rotor-plus-two-quasiparticle model has been used to describe the observed level structure. The pn interaction is shown to be of negligible effect. On the other hand, the introduction of a soft core is essential. The application of the VMI model with the parameters extracted from the 98Ru core yields a remarkably good agreement. This is the first time that the anomalous VMI root ( I 0 has been applied to a doubly odd nucleus.

High spin single particle states in Er 1 5 2 , 1 5 3

A spectroscopic investigation of yrast and near-yrast states in /sup 152/Er and /sup 153/Er is presented. We report measurements of prompt and delayed excitation functions, ..gamma..-..gamma.. coincidences, isomeric lifetimes, and ..gamma..-ray angular distribution, obtained chiefly from the reactions /sup 144/Sm(/sup 12/C,xn)/sup 152,153/Er using carbon beams of laboratory energy 65--95 MeV. The levels observed extend to a spin of J> or =43/2 and include two long-lived isomers in /sup 153/Er. The nuclear structure is discussed in terms of the shell model and compared with the systematic behavior of levels in N=84 and N=85 isotones.