Charge exchange collisions in gases in the presence of competing processes

Abstract

The slowing down of charged particles in noble gases has been investigated theoretically from the charge exchange regime down to thermal energy, where several processes such as ionisation, elastic and excitation as well as charge exchange collisions contribute to the energy loss. A formalism has been developed which allows one to calculate the rate of energy loss (dE/dt), the collision rate (dN/dt), the slowing down time, the neutral fraction and other quantities of interest directly from the cross sections of the atomic process involved. The formalism has been applied to the case of muons in He where two experimental observables, the fraction of the neutral species (muonium) and the muon spin depolarisation during charge exchange, have been calculated based on the atomic cross sections for muons and muonium obtained from the corresponding proton and hydrogen data by a simple scaling scheme.