Energy straggling of heavy charged particles in thick absorbers

The theory of energy straggling attempts to calculate F(E,S), where F(E,S)dE is the fraction of the heavy charged particles which have an energy between E and E+dE after a path length S has been traversed in absorbing medium. This paper develops a method of calculating F(E,S) for path lengths large enough so that F(E,S) is almost Gaussian. The method remains valid until a large fraction of the particles run out of energy. The theory is applied to calculations of F(E,S) for 50-MeV protons in Be and for 5.3-MeV α particles in air. The calculations for α particles in air are in good agreement with the experimental results of Rotondi and Gieger. The theory is also in agreement with numberical calculations by Tschalär.