Measurements of Inelastic Energy Loss in Large-AngleAr+on Ar Collisions at keV Energies

Abstract

Large-angle collisions of ${\mathrm{Ar}}^{+}$ ions with Ar atoms are studied in which the inelastic energy loss $Q$ is measured as a function of incident energy and scattering angle. Measurements are made at 3-, 6-, 12-, 25-, 50-, 75-, and 100-keV incident energies and the recoiling target particles are studied at several angles $\phi$ between 84° and 52°, corresponding to collisions where the scattered incident particle is scattered through angles $\theta$ between about 6° and 38°. The kinetic energies and scattering angles of the recoils are accurately measured, and this, together with the conservation equations, permits determination of the inelastic energy. The average value of the inelastic energy loss $\overline{Q}$ is plotted vs recoil angle $\phi$ and a separate curve is obtained for each incident energy. However, when the various $\overline{Q}$ values are plotted vs the calculated distance of closest approach, a universal curve is obtained which has an abrupt rise when this distance is 0.23 Å irrespective of energy.