Onset of collectivity in neutron-rich Fe isotopes: Toward a new island of inversion?

The lifetimes of the first excited 2+ states in 62Fe and 64Fe have been measured for the first time using the recoil-distance Doppler shift method after multinucleon transfer reactions in inverse kinematics. A sudden increase of collectivity from 62Fe to 64Fe is observed. The experimental results are compared with new largescale shell-model calculations and Hartree-Fock-Bogolyubov–based configuration-mixing calculations using the Gogny D1S interaction. The results give a deeper understanding of the mechanism leading to an onset of collectivity near 68Ni, which is compared with the situation in the so-called island of inversion around 32Mg.