Chapter 8 - Charge exchange

Abstract

This chapter discusses nonradiative or Coulomb capture. Charge changing reactions can be studied experimentally by passing an ion beam of known charge-state composition through a target and measuring the fraction of ions that have either captured or lost an electron. It is found that for excitation and ionization, first-order perturbation theory is a valid approximation, except for very small impact parameters where the interaction may become extremely strong. The presence of high-momentum components in initial and final states renders ls–ls capture the most important case at collision energies high above the matching energy. It is observed that capture cross sections calculated in the relativistic first-order Oppenheimer–Brinkman–Kramers approximation are larger than the experimental values. It is found that in analogy to the nonrelativistic case, it is necessary to construct first-order transition amplitude from the solutions of the asymptotic Dirac equations. A boundary-corrected first Born approximation for relativistic electron capture has been formulated. The relativistic eikonal approximation has been introduced and worked out for arbitrary initial and final states.