The Stopping Power for Structured Atomic Projectiles in Cold Or Ionized Solids.

A model has been developed to evaluate the stopping power for structured (not fully stripped) ion projectiles in cold (neutral) or ionized targets. The dominant contribution is computed in the local plasma approximation (LPA) which averages the stopping power of a free-electron gas (FEG) over the electron distribution of the target. Projectile structure is introduced by taking into account the charge distribution about the intruding ion. Corrections for treating the target as a local FEG are treated through a binding parameter and comparison to an alternate atomic-target formulation. The binding parameter is observed to scale in size with the degree of target ionization. Secondary corrections (Barkas and Bloch terms, to correct for departures from pure Rutherford scattering and from plane wave scattering, respectively) are also included. Projectile structure is treated only approximately through point effective charges. Two alternate derivations of the Bloch correction are seen to yield consistent results. Two forms of the Barkas term are considered: one including contributions from close collisions while the other does not. Inclusion of the Bloch correction limits the results to velocities which depend on both the projectile and target. Various projectile-target combinations have been calculated. The results deviate from st and ard tabulations by at most about 15% (often much less). This indicates it is possible to incorporate the actual projectile charge states in the stopping power formulae. The scaling of the binding parameter with target ionization restores some confidence in the LPA for use in ionized targets. The difference in treating the projectile as truly structured or as simply a point charge are not great for the ionized targets considered since the terms arising from true projectile structure tend to offset the difference.PhDNuclear engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161113/1/8621310.pd