Halo formation in neutron rich Ca nuclei

We have investigated the halo formation in the neutron rich Ca isotopes within the framework of recently proposed relativistic mean-field plus BCS (RMF+BCS) approach wherein the single particle continuum corresponding to the RMF is replaced by a set of discrete positive energy states for the calculation of pairing energy. For the neutron rich Ca isotopes in the vicinity of neutron drip-line, it is found that further addition of neutrons causes a rapid increase in the neutron rms radius with a very small increase in the binding energy, indicating thereby the occurrence of halos. This is essentially caused by the gradual filing in of the loosely bound 3s1/2 state. Interesting phenomena of accommodating several additional neutrons with almost negligible increase in binding energy is shown to be due to the pairing correlations (Authors)