Microscopic investigation of the 12Be spectroscopy

We analyze the 12Be spectrum with two microscopic methods. Microscopic cluster calculations are performed within the Generator Coordinate Method (GCM) framework. An extended two-cluster model which includes the 8He(0+,2+)+α, and 6He(0+,2+)+6He(0+,2+) channels is developed. It represents an extension of a previous work by Descouvemont and Baye where only the 0+ ground states of 8He and 6He were taken into account. The GCM calculations lead to a good description of the molecular band suggested by Freer et al. and by Saito et al. The 02+ isomeric state and the 22+ state are also well described by the GCM. New bands of positive and negative parities are proposed. This approach is complemented by No-Core Shell Model (NCSM) calculations, in order to clarify the structure of the ground state and the hypothesis of an associated rotational band. The GCM and NCSM calculations do not support the existence of a band built on the ground state.