Weakly-bound p3/2 neutrons and spin-response function in the many-body pair-correlation of neutron drip line nuclei

Solving the simplified model of the Hartree-Fock Bogoliubov equation in coordinate space with the correct asymptotic boundary conditions, the spin-orbit splitting, occupation probabilities, effective pair-gap, mean square radius, and spin-response function are studied for weakly bound p neutrons. As the binding energy of p3∕2 neutrons becomes small or approaches zero, the spin-orbit splitting p3∕2−p1∕2 in the one-body potential drastically decreases and, at the same time, the effective pair-gap for the p neutrons becomes small, while the occupation probability of the p3∕2 level decreases only slightly. Consequently, in that limit low-lying broader spin response with almost constant amount of total strength appears with the peak moving toward very low excitation energies