Low-lying intruder 1− state in 12Be and the melting of the N=8 shell closure

Inelastic scattering of the neutron-rich nucleus 12 Be on lead and carbon targets has been studied by measuring de-excitation γ rays in coincidence with scattered 12 Be. The strong γ -ray transition from the state at E x =2.68(3) MeV following E1 Coulomb excitation was observed for the lead target, leading to an assignment of J π =1 − for the excited state. The low excitation energy of this intruder 1 − state and the deduced large B (E1;0 g.s. + →1 − ) value of 0.051(13) e 2 fm 2 provide a consistent picture of the N =8 shell melting in 12 Be.