Theoretical and computational studies of electron and positron collisions with atomic and molecular systems

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Our research involves the calculation of the scattering of electrons and positrons from atomic and molecular systems. Positrons are the anti-particles of electrons and although they annihilate with electrons, they live long enough to scatter from atoms and molecules and for this scattering to be measured in the laboratory. In our calculations, we treat the positron as an electron but with the opposite electric charge. There is a simplification in that the positron is a distinct particle from those in its scattering target and therefore it cannot interchange with any of these particles the way an electron can. However, a positron and an electron can form a bound state, positronium. Positron scattering is a field of active research experimentally to investigate the interaction between matter and anti-matter and we will compare our results to these measurements to guide future studies.******Much of our research focuses on ionization where the incident electron or positron causes the ejection of one of the electrons initially bound in the target. Ionization is a difficult problem theoretically since the two outgoing charged particle interact through the coulomb force. This interaction can be treated in an average manner which results in a simplified calculation and gives reliable results in many cases. We will further investigate the effect that the inclusion of the full interaction has on the results of our calculations for ionization. ******We have developed a method of obtaining analytic static potentials for any molecule which is represented by the well-known Gaussian wave functions. Since the only input required for this method are the parameters for these wave functions, the amount of computer storage required is reduced by orders of magnitude and the accuracy of the results is governed solely by the accuracy of the wave functions themselves. We will exploit this method in calculating the ionization of large molecules of interest in medical treatments using x-rays or positrons.******We are able to deal with atomic and molecular systems ranging from the very small to the very large. Smaller systems can be treated using the Schroedinger equation but the Dirac equations are more appropriate to deal with scattering from heavy atoms. Heavy atoms exhibit fine-structure splitting of the valence shells of sufficient magnitude that can be resolved experimentally and Dirac-Fock wave functions used for the target include this splitting and provide distinct energies and wave functions to describe this physical property of heavy systems. ******Much of the data we produce is of interest in the modeling of plasmas which are extensively used in industry. We have made these data available publicly through a website devoted to the modeling community. We will continue our efforts to investigate the use of these data in the modeling of plasmas. We will also model fusion plasmas in conjunction with ongoing experimental work in this field.*****