New information from Bremsstrahlung: new calculations for new experiments

The approaches to the description of Bremsstrahlung and the extent to which they are in accord with present experimental information are reviewed. Beyond simple Born approximation predictions, the standard theoretical approach for the doubly differential cross section at x-ray and soft γ-ray energies is based on the relativistic independent-particle-approximation code of Tseng. There are new results at low energies, both where a classical domain is approached and at energies comparable to transition energies, where the correlation effects of polarization Bremsstrahlung can dominate. Recently Tseng's code has been extended, by rearranging the manner in which radial matrix elements are summed, to provide predictions for the triply differential cross section, viewed as providing a more sensitive probe of the validity of external-field quantum electrodynamics. The types of information about the atom and about classical, nonrelativistic and relativistic quantum descriptions of these processes are discussed. (author). 31 refs., 3 figs