Review of experimental cross sections for K-shell ionization by light ions

Abstract

We review experimental K-shell ionization cross sections using a data file containing about 7800 total X-ray or Auger production cross sections taken from the literature for which Z 1/ Z 2<0.3, where Z 1 and Z 2 are the atomic numbers of projectile and target. We compare various recent collections of K-shell fluorescence yields ω, and we use Krause's tables to convert the data to ionization cross sections. For every projectile, we normalize these data using the theoretical cross section due to Brandt and Lapicki (ECPSSR). We show them plotted versus log ξ (where ξ is the scaled projectile velocity) in the appendix, and we average them in equal intervals ° log ξ. A statistical criterion is used to exclude references with discrepant data. We find that the average normalized cross section s̄ is mostly close unity (i.e., ECPSSR describes the data well), but that there are also significant deviations at certain values of ξ. For almost all projectiles, s decreases below unity for log ξ<-0.6. For protons, we find in addition a small dependence of s upon Z 2 for small and for large log ξ. We approximate s by analytical functions of log ξ and thus produce “reference” cross sections for selected proton energies and targets. For heavier projectiles (and also for protons on light targets), additional systematic deviations develop: a maximum of s around log ξ=−0.6 and a minimum around log ξ=−0.3. Above log ξ=−0.1, the influence of multiple ionization and of electron capture by the projectile becomes noticeable with increasing Z 1. X-ray cross sections for light solid or gaseous targets ( Z 2<11) are discussed separately since the fluorescence yield may here depend on the chemical state. Here we find it better to use ω from Krause's table for gaseous targets, also for solid targets ( Z 2>5).