Spectroscopy and lifetime measurements of states in $^{76}$Kr populated in $^{76}$Rb decay

The properties of the excited states of $^{76}$Kr, populated in the decay of $^{76}$Rb produced at ISOLDE isotopic separator, have been investigated by using K-conversion electron, $\gamma$-ray, and $\gamma\gamma$ coincidence measurements. The lifetimes of several levels have been measured by means of the Advanced Time-Delayed $\beta\gamma\gamma (t)$ 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 $J^{\pi} =2^{-}$ 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 $E$0 and $E$2 transitions de-exciting the 0$^{+}_{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.