Configuration interaction calculations of cross sections for proton stopping reactions

Abstract

Purpose: To illustrate the role of quantum mechanical electronic structure methods in providing accurate predictions of the cross sections for ionization and electron capture processes that occur as a result of proton collisions in the high-eV to low-keV energy region.Methods: Calculations are carried out to compute potential curves and non-adiabatic coupling elements for a variety of collision partners employing the ab initio multireference single- and double-excitation configuration interaction (MRD-CI) method. These results are used as input for the electronic-state close-coupling (ESCC) method in order to compute cross sections for various transitions that occur because of collisions.Results: Emphasis is placed on proton-molecule collisions that play a key role in various medical applications as well as in astrophysics and nano-scale materials manufacturing. Examples discussed include the Na-He pair of atoms of interest in recent astrophysical observations, proton collisions with various hydrocarbons and also with water and oxygen, and key ionic products such as H2O+ and H3O+ .Conclusions: The computed cross sections provide a detailed picture of radiation damage dynamics in Monte Carlo simulations. This information can potentially enhance the efficiency of proton beam focusing and also reduce undesirable side effects on body tissues.