Pairing effects on vorticity of incident neutron currents at quasiparticle resonance energies in n−A elastic scattering

Abstract

In this study, we analyzed how the incident neutron current is affected by the pairing effect in neutron-nucleus scattering described within the framework of Hartree-Fock-Bogoliubov theory by performing numerical calculations in terms of current, vorticity, and circulation of the incident neutron current. We found that the pairing effect on the incident neutron flux is completely different between particle-type and hole-type quasiparticle resonances. In the case of h-type quasiparticle resonance, the pairing acts to prevent the neutron flux from entering the nucleus, reducing circulation. In the case of p-type quasiparticle resonance, pairing acts to reduce circulation at energies lower than the resonance energy, but, at energies higher than the resonance energy, the effect of pairing on the neutron flux is reversed and, conversely, circulation is increased. These properties are consistent with the approximate expression for the vorticity characteristics at p-type and h-type resonances, implying that the vorticity appearing near p-type resonances due to the pair-correlation effect is inversely proportional to the resonance width (proportional to the resonance lifetime). In contrast, at h-type resonances, the pair-correlation effect has the effect of canceling out the vortex created by MF scattering and is independent of the resonance width.