Prolate-oblate shape coexistence in 75Kr

Abstract

The collective bands of 75Kr were extended up to spin 45 2 using the compound reactions 50Cr( 28Si,2pn), 54Fe( 24Mg,2pn) and 58Ni( 20Ne,2pn) 75Kr. Lifetimes were measured by RDDS with nine OSIRIS detectors in coincidence. Mixing ratios were determined by measurements of internal conversion coefficients, angular distribution and correlations. Deviations between different measurements are explained by the short lifetimes leading to angle dependent intensity losses due to Doppler shift. Spins and parities were assigned from angular distributions, excitation functions and DCO ratios measured with the OSIRIS_12 spectrometer. The band head spin of the negative parity yrast band was established as 3 2 via DCO ratios and internal conversion coefficients. Further bands at low excitation energy were found. In accordance to Woods-Saxon cranking model calculations, these weaker populated sidebands are interpreted to be built on oblate deformed intrinsic states ( β 2 ≈ −0.2), while the strongly populated bands are built on prolate deformed states ( β 2 ≈ +0.4). The interpretation of the 1qp g 9 2 yrare band, to be generated from oblate deformation, is further supported by ΔI = 0 transitions into the yrast band and a similar oblate deformed g 9 2 structure in the isotone 73Se. The experimental level energies, branching ratios, transition probabilities and mixing ratios are compared to rotor model calculations. The deviations between experiment and rotor model calculations are interpreted to be based on mixing between prolate and oblate states.