Abstract
The role of electron-electron correlation in both single and double electron ionization cross sections for a bare ion projectile incident on helium is investigated. We calculate reference cross sections in which correlation is deliberately turned off during the collision, and compare them to results where we have tried to treat correlation exactly. We discuss three reference cross section algorithms: the Frozen Correlation Approximation of Martin and Salin; a no-cut Forced Impulse Method of Reading and Ford; and a new No-Correlation algorithm. We obtain exact results from a one-cut FIM calculation. In principle the number of cuts needed is determined only by increasing them until convergence is obtained but the one-cut version is supposed to be accurate in the high energy range: 200keV-7MeV/amu. We discover that correlation is more important for proton than anti-proton projectiles; its effect on the cross section increases as the energy of the projectile is lowered; and it is most important at small impact parameters. At the lowest energies the differences between the no-cut and one-cut FIM cross sections lead us to doubt the accuracy of the FIM one-cut method for projectile energies below 200keV. Experimental cross sections for anti-proton projectiles down to 12keV have been measured recently been measured. To address these, we test the efficacy of the onecut FIM computer code in this low energy regime. Results point to the neccessity for a multi-cut FIM code in order to obtain converged cross sections for this system.
Bronk, Timothy Edward (1996). Intermediate correlation in proton and anti-proton ionization of helium. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -B753.