Systematics of heavy-ion charge-exchange straggling

Abstract

The dependence of heavy-ion charge-exchange straggling on the beam energy has been studied theoretically for several ion-target combinations. Our previous work addressed ions up to krypton, while the present study focuses on heavier ions, especially uranium. Particular attention has been paid to a multiple-peak structure which has been predicted theoretically in our previous work. For high-Z 1 and high-Z 2 systems, exemplified by U in Au, we identify three maxima in the energy dependence of charge-exchange straggling, while the overall magnitude is comparable with that of collisional straggling. Conversely, for U in C, charge-exchange straggling dominates, but only two peaks lie in the energy range where we presently are able to produce credible predictions. For U-Al we find good agreement with experiment in the energy range around the high-energy maximum. The position of the high-energy peak-which is related to processes in the projectile K shellis found to scale as Z 2 1 , in contrast to the semi-empirical Z 3=2 1 dependence proposed by Yang et al. Measurements for heavy ions in heavy targets are suggested in order to reconcile a major discrepancy between the present calculations and the frequently-used formula by Yang et al.

Energy loss and straggling of MeV Si ions in gases

“…This structure could not be resolved with the current uncertainties of the measurement. In order to demonstrate the predicted multi-peak structure in the energy-loss straggling either higher measurement precision is needed (which is difficult to achieve with the current setup) or one has to look for another beam-target combination that shows a pronounced peak similar to Si-He [7]. Figure 6: Stopping cross sections for Si in in He, N 2 , Ne, Ar and Kr gases.…”

“…Sigmund et al [3,4,5,6,7] have recently made significant progress in understanding the different important contributions to heavy-ion straggling as a function of energy. Theoretically linear straggling (as a result of the interaction with independent target electrons) and non-linear straggling (including bunching of electrons in atoms, packing of atoms in molecules, crystals etc.…”