Backscattering of Singly Positive Atomic Helium and Singly Positive Atomic Hydrogen Particles from Ultra Thin Films in the Energy Range 50-100 KEV.

In order to test the applicability of the potential arising from Lindhard's Thomas-Fermi treatment of the interaction between two atoms, the elastic collision cross sections of He (+) and H(+) ions incident on targets of Au, Ag, Cu, Bi, Ni, and In were measured. The ions were accelerated to energies ranging from 50 keV to 100 keV and were made to collide with the target material. Those ions that had been scattered through a laboratory angle of 150 deg were detected and energy analyzed. The targets consisted of vacuum depositions of the target material of density equivalent to less than a monolayer, deposited on commercially available, glass mounted, 40 microgram/sq cm carbon foils. The results obtained clearly illustrate the efficacy of the Lindhard description for elastic collisions in this energy range. In addition, they further show that fractional monolayer vacuum evaporated targets can be used for these measurements.