Reduced transition probabilities in ^80,82,84,86Se

The systematic investigation of exotic nuclei around the N=50 shell-closure is of high interest for nuclear structure research, as single particle-, particle-hole- and collective excitations coexist in this region of nuclei. Transition probabilities from lifetimes of excited states give insight to nuclear structure and allow to probe nuclear models, i.e. the nuclear shell model. We performed a recoil-distance-Doppler-shift experiment at the INFN, Legnaro, using the Cologne Plunger for the RDDS technique, the PRISMA magnetic spectrometer for the event-by-event particle identification and the AGATA spectrometer in its demonstrator configuration for the γ-ray detection and tracking. Using a ⁸²Se beam and a ²³⁸U target ^80,84,86Se nuclei were produced in excited states via multi-neutron transfer reactions. ⁸²Se nuclei were excited via multiple-step Coulomb excitation. Because of low statistics γγ-coincidences could not be used for the lifetime analysis. Therefore special care has to be taken to consider all relevant feeding. In order to better estimate effects caused by unobserved side feeding different gates on the total kinetic energy loss of the recoils were investigated. Experimental results on transition probabilities in ^80,82,84,86Se isotopes are presented and discussed in terms of large-scale shell-model calculations we performed.