Magnetic Field Effect on Masses of Atomic Nuclei

Abstract

The magnetism of nuclides in the outer crusts of neutron stars is considered. Employing the shell correction treatment, we demonstrate that strong magnetic fields significantly affect shell oscillations in nuclear masses. The phase shift in shell oscillations is shown to be the main feature of the field effect. Such a phase change originates from the Pauli magnetic response associated with the relative shift of spin-up and spin-down energy levels. The neutron shell correction energy behaves almost periodically as a function of the field strength with slightly enhanced amplitude of shell oscillations at large fields. The period of the sign change is determined by the energy difference between neighbor levels. The proton shell correction energy displays an anomalous dependence on the field strength. The proton orbital magnetism enhances the nuclear shell effect especially when the field influence is comparable to the spin-orbit coupling. The nuclear magic numbers are demonstrated to depend considerably on the magnetic field on the strength scale B ~ 1016-1017 G relevant for, e.g., soft gamma repeaters and anomalous X-ray pulsars.