Intermediate-energy positron and electron bremsstrahlung from atoms

Using a relativistic partial-wave method we calculated numerically the photon energy-angle distributions for positron and electron bremsstrahlung in the field of atoms with atomic number Z = 1, 13, and 79 for kinetic energies of incident positrons or electrons T-1 = 1.0, 2.0, and 2.5 MeV. In this intermediate-energy region, our studies indicate that the Born approximation predictions agree quite well with our partial-wave results for the shape of the photon energy-angle distribution of the positron bremsstrahlung. For high-Z elements, the Born approximation predictions are not good for the shape of the photon energy-angle distribution of electron bremsstrahlung. The Born approximation results can be improved if one multiplies by the Elwert-factor which is independent of photon angle. Our partial-wave results also indicate that the shape of the photon energy-angle distribution of positron or electron bremsstrahlung is almost independent of atomic-electron screening.