Effect of neutron excess on Delta excitations in exotic nuclei - art. no. 014301

The effects of neutron excess on the formation of Delta(3,3) resonance stat es in exotic nuclei at equilibrium and under large amplitude compression ha ve been investigated within the radial constraint spherical Hartree-Fock me thod. An effective Hamiltonian has been used which includes the Delta degre e of freedom explicitly. Results are presented for O-28, Ca-60, and Ca-70 i n a model space of seven major oscillator shells and eight Delta orbitals. The results show that the formation of the Delta's depends strongly on the amount of neutron excess in the nuclear system. In contrast to previous wor k where we found no Delta's in O-16 and Ca-40 at equilibrium, these results show that a significant amount of Delta's exists at equilibrium in exotic isotopes. In addition, as the nucleus is compressed to a density of 2.5 tim es the ordinary nuclear density, the percentage of the Delta's rises to 3%, 5%, and 7% of the total number of all baryons in O-28, Ca-60, and Ca-70, r espectively. This suggests a parametrization for the percentage of the Delt a's created at 2.5 times the normal density of the form 0.25(N-Z)%. The res ults are consistent with the theoretical prediction of the formation of Del ta matter in neutron-rich matter at high compression.