The Threshold Laws for Electron-Atom and Positron-Atom Impact Ionization

In view of the fact I have long been interested in the electron-atom impact ionization problem, and have published several papers on it over the years, I would like in this talk to review only the most salient aspects of my work, which has only recently culminated with what I believe is a derivation of the correct threshold law. By way of introduction let me emphasize that because the problem deals with three separating charged particles at the lowest energy at which they can escape from one another, this is the most basic three-body problem in the continuum involving Coulomb (i.e., long-range) forces. At the same time it also involves quantum mechanics in a very fundamental way, in my opinion. What I would like to do here is to emphasize, schematically through a series of figures, aspects of my approach -- the Coulomb-dipole theory -- which I did not dwell upon in my most recent articles including also the positron-atom impact ionization problem and two-electron photodetachment of H-. The latter has particular relevance for this conference in view of the fact that the newest experiment involves the accelerator (LAMPF) in a basic way.