Theoretical approaches for hard electron bremsstrahlung and their scaling properties in the ultrarelativistic regime

Abstract

Bremsstrahlung angular and frequency distributions from 35-MeV electrons colliding with lead are calculated within the Dirac partial-wave (DW) theory. These benchmark results are compared with the Dirac-asymptotic Sommerfeld-Maue approach, with an analytical approximation to this DaSM model, and with the Sommerfeld-Maue (SM) theory, in order to investigate the validity of these simpler theories for photons with frequencies beyond 25 MeV. Scaling properties with respect to the collision energy, the photon emission angle, and the energy of the scattered electron are used to extend the predictions at 35 MeV to higher collision energies. For the angle-integrated photon spectrum a Green's-function-based theory by Milstein and coworkers [J. Exp. Theor. Phys. 100, 1 (2005)] serves as a complement to the DW theory at the lower photon frequencies. Earlier conjectures are confirmed that, for the singly differential cross section, the SM theory is applicable for frequencies at least some 5 MeV below the short-wavelength limit.