Shape coexistence in the light krypton isotopes was studied in two low-energy Coulomb excitation experiments using radioactive 74 Kr and 76 Kr beams from the SPIRAL facility at GANIL. The ground-state bands in both isotopes were populated up to the 8 + state via multi-step Coulomb excitation, and several non-yrast states were observed. Large sets of matrix elements were extracted for both nuclei from the observed γ -ray yields. Diagonal matrix elements were determined by utilizing the reorientation effect. In both isotopes the spectroscopic quadrupole moments for the ground-state bands and the bands based on excited 0 + 2 states are found to have opposite signs. The experimental data are interpreted within a phenomenological two-band mixing model and model-independent quadrupole invariants are deduced for the relevant 0 + states using the complete sets of matrix elements and the formalism of quadrupole sum rules. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and are compared both with the experimental results and with recent calculations using the Skyrme SLy6 effective interaction and the full generator-coordinate method restricted to axial shapes.

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Two low lying positive-parity bands in 130Cs have been examined for chiral signatures. Small energy differences between the two bands, which have been previously observed, have been confirmed and the bands, as well as the number of transitions within and between the bands, extended. The intraband B(M1)/B(E2) ratios and B(M1)intraband/B(M1)interband ratios and the energy staggering parameter, S(I), have been deduced for these partner bands. The results are found to be consistent with a chiral interpretation for the two structures. Core–quasiparticle coupling model calculations have been performed to study 130Cs assuming a triaxial core. The experimental level energies and electromagnetic properties of the bands, resulting from the configuration, are reasonably well reproduced by the model, providing further evidence in support of the chiral interpretation of the two structures.