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

Inelastic scattering of the neutron-rich nucleus Be-12 on lead and carbon targets has been studied by measuring de-excitation gamma rays in coincidence with scattered Be-12. The strong gamma -ray transition from the state at E-x = 2.68(3) MeV following El Coulomb excitation was observed for the lead target, leading to an assignment of J(pi) = 1(-) for the excited state. The low excitation energy of this intruder 1(-) state and the deduced large B(El; O-g.s.(+) --> 1(-)) value of 0.051(13)e(2) fm(2) provide a consistent picture of the N = 8 shell melting in Be-12. (C) 2000 Elsevier Science B.V. All rights reserved.