RUI: Positronium Scattering By Atoms, Molecules and Surfaces

Oregon Institute Of Technology, Klamath Falls OR

Investigators

Abstract

Positronium (Ps) is the bound state of an electron and positron. In this project the PI will study the interaction of the Ps atom with a variety of atoms and molecules, by developing models of these interactions and then calculating scattering cross sections with these targets. Electron and positron scattering has been studied quite extensively while Ps scattering has been studied relatively little in comparison. This is partly because Ps is a composite object which makes both theory and experiment more difficult. Recently, experiments have shown that electron and Ps scattering are surprisingly similar over a wide range of projectile velocities. At very low Ps velocities there is some discrepancy between experiment and theory, and fundamental questions remain to be answered. This work can help to understand the similarity at higher velocities and to resolve the discrepancy at low velocities. These studies can provide insight into the fundamental interactions between matter and anti-matter and help to provide a better understanding of technologies that involve Ps such as Positron Emission Tomography (PET) and the probing of defects in materials. Undergraduate students are involved in this research with the goal of providing them with an opportunity to apply mathematical methods to solve real world physical problems. In this project the PI will study Ps collisions with atoms, molecules and surfaces. The plan is to calculate elastic scattering cross sections as well as ionization (Ps break-up) cross sections for a variety of atomic and molecular targets. To describe the interaction between Ps and the target atom or molecule the PI will use a free electron gas model that has been previously successfully used to describe the exchange and correlation effects in Ps collisions with rare-gas atoms and molecular nitrogen. The PI will also employ an orthogonalizing pseudopotential model to take account of the repulsive effect of the Pauli exclusion principle. The focus will be on extending these models to molecules, as well as to atomic targets besides the rare-gases. The PI will also seek to better understand the Ps-atom/molecule interaction by seeking to improve the approximations inherent in the models. The PI has previously developed a binary encounter model for calculation of the ionization cross section which will allow calculation of total cross sections for new atomic and molecular targets. The PI also plans to extend the models to study the scattering of Ps with surfaces such as LiF. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.