An empirical approach to the stopping power of solids and gases for ions from 3Li to 18Ar

Abstract

A large collection of stopping power data for projectiles from 3Li to 18Ar is investigated as a possible basis for producing a table of stopping powers. We divide the experimental stopping powers for a particular projectile (nuclear charge Z 1) by those for alpha particles in the same element, as given in ICRU Report 49. With proper normalization, we then obtain experimental stopping power ratios S rel that lie approximately on a single curve, provided we treat solid and gaseous targets separately, and provided we exclude H 2 and He targets. For every projectile, this curve is then fitted by a 3-parameter sigmoid function S rel= S rel( a, b, c). We find that the three parameters a, b and c depend smoothly on Z 1 and can themselves be fitted by suitable functions a f, b f and c f of Z 1, separately for solid and gaseous targets. The low energy limit (coefficient a) for solids agrees approximately with the prediction by Lindhard and Scharff. We find that a gas< a sol in almost all cases. Introducing the coefficients a f , b f and c f in S rel, we can calculate the stopping power for any ion (3⩽ Z 1⩽18), and for any element (except H 2 and He) and any mixture or compound contained in the ICRU table.