Energy Distribution of Electrons in the Migdal Model of Atomic Ionization

The process of ionization that is due to the Migdal effect and which occurs in the elastic scattering of a heavy neutral particle, including a weakly interacting massive particle (WIMP), on a noble-gas atom in the case of its small recoil energy is considered. The mean number of primary and secondary electrons emitted in an individual event of such ionization is estimated, and the energy distributions of primary electrons are obtained. The calculations were performed for various noble-gas atoms with allowance for experimental data on their ionization by photons.