Constraints on two-neutron separation energy in the Borromean C-22 nucleus

The recently extracted matter radius of carbon isotope C-22 allows us to estimate the mean-square distance of a halo neutron with respect to the center-of-mass of this nucleus. By considering this information, we suggest an energy region for an experimental investigation of the unbound C-21 virtual state. Our analysis, in a renormalized zero-ranged three-body model, also indicates that the two-neutron separation energy in C-22 is expected to be found below similar to 0.4 MeV, where the C-22 is approximated by a Borromean configuration with a pointlike C-20 and two s-wave halo neutrons. A virtual-state energy of C-21 close to zero, would make the C-22, within Borromean nuclei configurations, the most promising candidate to present an excited bound Efimov state or a continuum three-body resonance. (C) 2011 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq