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

A large collection of stopping power data for projectiles from Li-3 to Ar-1 8 is investigated as a possible basis for producing a table of stopping pow ers. 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 experim ental stopping power ratios S-rel that lie approximately on a single curve, provided we treat solid and gaseous targets separately, and provided we ex clude H-2 and He targets. For every projectile, this curve is then fitted b y 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 f itted by suitable functions ar, bf and cf of Z1, separately for solid and g aseous targets. The low energy limit (coefficient a) for solids agrees appr oximately 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 less than or equal to Z(1) less than or equal to 18), and for any element (except H-2 and He) and any mixture or compound contained in the ICRU table. (C) 2001 Elsevier Science B.V. All rights reserved.