Investigating the collectivity of intruder states along N=49 isotones

Intruder states that originate from the promotion of neutrons across the N=50 shell gap are observed along the N=49 isotones (79Zn, 81Ge, 83Se, 85Kr), with the lowest energy in 83Se. The reduction of the N=50 shell gap towards Ni favors the lowering in the energy of these states. Moreover, since the Se nucleus (Z=34) is in the middle of the proton fp-shell (28≤Z≤40), it should have the maximum quadrupole correlations, lowering further the energy of these deformed configurations. This makes Se a good candidate for understanding the collectivity of the particle-hole intruder states in this region. Such information could also be used as a testing ground for theoretical models aiming to describe the region in the vicinity of 78Ni. An experiment aiming to measure the lifetime of the 540-keV 1/2+ and 1100-keV 3/2+ intruder states of 83Se was performed at LNL and is reported in this work.