Comments on the Calculation of Relativistic Bremsstrahlung Cross Sections

Recent attempts to calculate relativistic bremsstrahlung cross sections in the intermediate energy region are discussed, using results from an independent exact numerical calculation. The numerical work of Brysk, Zerby, and Penny gives quite good results for the bremsstrahlung cross section, differential only in photon energy, but significantly underestimates and over-estimates the cross section, differential in photon energy and angle, in small-photon-angle regions and in large-photon-angle regions, respectively. The approximate analytical results of Elwert and Haug are quite good for low atomic number $Z$, but we can already see deviations for $Z=13\mathrm{}$. For $Z=79\mathrm{}$, their theory underestimates the cross section by large factors.