Charge States and Charge-Changing Cross Sections of Fast Heavy Ions Penetrating Through Gaseous and Solid Media

Abstract

This review surveys the experimental and theoretical situation concerning charge states and charge-changing cross sections of heavy ions up to and including uranium, which penetrate through gaseous and solid targets with velocities primarily in the range ${v}_{0}lvlZ{v}_{0}$ (${v}_{0}=\frac{{e}^{2}}{\ensuremath{\hbar}}=2.188\ifmmode\times\else\texttimes\fi{}{10}^{8}$ cm/sec). Particular emphasis is given to ions with atomic numbers in the range $16\ensuremath{\le}Z\ensuremath{\le}92$. The published literature is covered through August 1971. General physical and mathematical relations are outlined which describe the composition of charge states in a heavy-ion beam which passes through matter. Recent experimental techniques and methods of data analysis are summarized. Extensive experimental results on heavy-ion equilibrium charge state distributions, average equilibrium charge states, and cross sections for capture and loss of one or more electrons in single encounters with target atoms are presented and critically examined. The data extend to ions as heavy as uranium and energies up to \ensuremath{\sim}400 MeV. Systematic trends are emphasized and generalizations are discussed which allow interpolations and to some extent extrapolations of the data to be made to ranges which have not been investigated experimentally. Attention is given to the cross sections for multiple-electron loss which are relatively large but which are poorly understood. We deal with effects of residual ion excitation on charge-changing collisions in the light of recent experimental results. It is shown that the average equilibrium charge of heavy ions can be approximated by utilizing both theoretical concepts which originate from the work of Bohr and Lamb, and semiempirical relations which are based on observed regularities of the data. Recent interpretations of phenomena associated with density effects, i.e., with the increase of projectile ionization which is observed for increasing target densities, are scrutinized and refinements of the theory by Bohr and Lindhard are explored.