The effect of apparatus geometry on H+-H, H+-D and D+-D charge-exchange cross sections

Abstract

The cross section Q_x for charge exchange between an incident ion and a target atom is usually measured by counting the number of ions scattered outside a cone about the incident direction. Only if the ion and atom have equal mass and if the semi-vertical angle ½ of the laboratory cone be 45°, is the number of ions counted known to equal the total number of exchange ions. Otherwise, the measured cross section Q() does not equal Q_x. It is nevertheless shown that, for H⁺-H, H⁺-D and D⁺-D, Q() and Q_x differ negligibly except for small at energies below 100 ev.