Energy loss and straggling of protons and helium ions traversing some thin solid foils.

Abstract

Absolute measurements of stopping powers and energy straggling for hydrogen and helium-ion beams in Ge, Se, Pd, Ag, Sb, and Bi in the energy range 20 < £ < 260 keV were performed by the method of determining the energy loss suffered by an ion beam which has traversed a thin film. The measured stopping powers fit reasonably well with those of other authors obtained at higher and lower ion energies. Agreement with theoretical predictions for energies > 100 keV/amu is found to be better for hydrogen than it is for helium beams. The Z2 dependence of the stopping power for hydrogen projectiles is discussed including measurements of other authors performed on other elements, and is found to agree in shape with that for helium for ion velocities v > 2 a.u., but there is evidence that it begins to differ with decreasing v. It is deduced from the present measurements that for hydrogen as well as helium ions the amplitude of oscillations of the Z2 dependence increases with decreasing ion velocity, reaching a máximum at ti = 1.4 a.u. The Lindhard-Scharff theory is found to be in satisfactory agreement with the measured energy straggling.