Interaction Between the Neutron Magnetic Moment and the Nuclear Coulomb Field in Neutron Polarization

Neutrons scattered through small angles by heavy nuclei are polarized by the interaction between the magnetic moment of the neutron and the electric field of the nucleus. Of the several approximate methods that have been used to estimate the magnitude of this effect, none are sufficiently general to permit the simultaneous consideration of a realistic nuclear potential that includes a spin-orbit interaction. Therefore such estimates are valid only for small angles of scatter (≲5-10°). A more nearly exact calculation based on an optical-model potential that includes a spin-orbit term is described in this paper. The calculation is based on a generalization of the usual Born approximation. This "generalized" method can be applied to a variety of problems in which the scattering potential is separable into a strong short-range term and a relatively weak long-range one. The results of this calculation are compared with data that originally indicated the possibility of an extranuclear contribution to the polarization of ∼1.0-MeV neutrons scattered through an angle of 24°. This comparison indicates that the electromagnetic interaction can account for a substantial part of the polarization observed at this "large" angle—even for neutrons scattered from nuclei with moderate charge ($Z\gtrsim 40$).