On the theory of atomic ionization following alpha decay

The -decay of a nucleus may cause atomic ionization. One of the basic assumptions of Migdal's original paper, which is the prototype of all later calculations for this process, is to treat the -particle outside the nuclear region classically as a point charge moving along a definite trajectory. In contrast to this picture, in the standard quantum-mechanical model of the -decay, the -particle is represented by a wave function that, after tunneling through the Coulomb barrier at the nuclear surface, propagates outwards as a spherical wave. We compare these two pictures within a three-body model, clarify the conditions under which the full quantum-mechanical calculation and its semiclassical counterpart give similar results and also point out the origin of their possible discrepancies.This paper is dedicated to the memory of A. B. Migdal. His bright physical intuition, which guided him in his pioneering work on this subject—as in many cases later on-, proved to be essentially correct