[A simple formula for determination of the mean electron energy in a body irradiated by fast electrons (author's transl)].

A simple formula for calculation of the mean electron energy from primary energy and depth of irradiation is derived. The formula has been verified for substances with low atomic numbers (Z less than or equal to 6) and by experiments using primary electron energies from 5 to 15 MeV and irradiation depths up to 80% of the practical range, which corresponds to mean electron energies from 2.2 to 15 MeV. For this purpose, the relative mass stopping-power ratios water/air which have been obtained using the formula together with valid standard tables (ICRU, DIN) and literature were compared with those found by absolute dosimetry by means of a graphite double extrapolation chamber (primary standard). An optimal accordance with the standard values for non-restricted mass collision stopping-power, as indicated by Berger and Seltzer, was the result (better than +0.6 to -0.05%). The verification of a formula known from literature (Harder) revealed similar results (+0.4 to -0.8%).