Population inversion in the surface channeling of positrons

Darwin's scattering theory is generalized to the case of the small-angle incidence of positrons on a crystal surface when the amplitude of forward scattering by the surface is relatively high (q0 is about 1), which corresponds to the case of the plane channeling of positrons. It is shown that the channeling of positrons under these conditions allows an ideal population inversion (for j equal to or greater than 2) with a maximum concentration difference. This regime is also characterized by the absence of bounds on the active zone length, with particles introduced into the channels over the length of the crystallographic plane, and by an abrupt increase in the permissible beam current density due to its grazing incidence on the crystal's face.