Spectroscopy and lifetime measurements of states in Kr 76populated in Rb 76 decay

The properties of the excited states of 76Kr, populated in the decay of 76Rb produced at ISOLDE isotopic separator, have been investigated by using K-conversion electron, γ -ray, and γ -γ coincidence measurements. The lifetimes of several levels have been measured by means of the advanced time-delayed βγγ(t) method. The identification of 19 new levels and 55 transitions and the information deduced on spin and/or parity of the observed states from K-conversion coefficients, log ft values and decay properties have led to an improved knowledge of the level scheme. In particular, six 1− states have been definitely identified and J π = 2− has been assigned to the 2227 keV level, on which a band proposed to have negative-parity and even-spin had been previously observed. The strengths of the E0 and E2 transitions deexciting the 0+2 and 0+3 states (the latter is here identified with the state at 1598 keV) have been measured. The experimental data concerning the 0+2 state have been analyzed in a simple two states mixing model and in the framework of the proton-neutron interacting boson model.