Atomic charge exchange between fast helium ions and targets from carbon to bismuth at β=0.36

Abstract

Equilibrium charge-state distributions for singly and doubly ionized $^{3}\mathrm{He}$ ions of energy E${(}^{3}$He)=200 MeV (\ensuremath{\beta}=0.36) have been measured for atomic targets ranging from carbon to bismuth (Z=6,14,28,40,50,67,73,83). A magnetic spectrometer was used to simultaneously measure the rate of $^{3}\mathrm{He}^{+}$ ions and the current of the incident beam of $^{3}\mathrm{He}^{2+}$ ions. The ratio of the fraction of ions Y${(}^{3}$${\mathrm{He}}^{+}$/Y${(}^{3}$${\mathrm{He}}^{2+}$) was found to increase from 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ for Z=6 to 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ for Z=83. Very good agreement with the experimental ratios was obtained for calculated ratios based on theoretical stripping (ionization) and capture cross sections. The cross sections are dominated by capture from K orbits only for atoms up to about Z=25. For target atoms with high Z, contributions up to principal quantum numbers n=4 (N orbits) must be included.