Atomic-field bremsstrahlung at zero degrees

Bremsstrahlung spectra have been measured for elements with atomic numbers ranging from 29 to 92 at 0deg, 30deg, 45deg, and 90deg photon emission angle with a 70-keV electron beam. In an earlier experiment, the electron beam had been deflected away from the detector by a magnet; however, the dispersion of the electron beam in the target created a background that could not be subtracted out easily. Hence, in this work, we introduce an alternate approach to magnetic deflection. Here, the incident or scattered beam is stopped completely by adding a thick carbon backing to the thin-film target. The thick-target bremsstrahlung from the low-Z backing, which decreases linearly to zero at the end point, can be subtracted out, and reliable measurements of the cross section can be made over a wide range of radiated photon energy. Typical results will be presented and compared with theory. Theory is found to reproduce well the shape of the radiated photon energy spectrum at 30deg, 45deg, and 90deg, but there is a significant discrepancy between theory and experiment for 0deg. (orig.)