Investigations of the Interactions of Radiation with Matter.

Abstract : Theoretical studies of the interaction of charged particles and electromagnetic radiation with matter have been performed. Particular emphasis has been given to ionizing radiation and the details of energy deposition by the radiation. New phenomena have been discovered in the area of ionization in ion- atom and atom-atom collisions. Models of electron impact ionization of atoms and molecules have been extended to the relativistic range. In addition, relativistic effects in the photoionization of very heavy atom and ions have been delineated in detail for the first time. Finally, a number of investigations of various aspects of photoionization of excited atom have been carried out which have given new insight into the process, both for outer and inner shell ionization. Of particular interest is the discovery that inner shell photoionization of excited atoms is primarily a many-body process.