Shape coexistence in 74Kr and 76Kr

Abstract

The coexistence of prolate and oblate shapes in the light krypton isotopes was investigated by Coulomb excitation of radioactive 74Kr and 76Kr beams at sub-barrier energies from the SPIRAL facility at GANIL. States up to the 8+ in the ground-state band and several non-yrast states were populated in both cases via multi-step Coulomb excitation. A large set of both transitional and diagonal matrix elements was extracted from the measured differential Coulomb excitation cross sections. A complementary lifetime measurement using the recoil-distance Doppler shift method gave important constraints for the determination of the matrix elements. The signs of the quadrupole moments of the yrast and excited bands represent direct evidence for the coexistence of prolate and oblate shapes in both isotopes under study. The results are compared to recent configuration mixing calculations based on the generator coordinate method and Skyrme Hartree-Fock-Bogolyiubov mean-field states.