Measurements of the differential cross sections for K-shell ionization and bremsstahlung with a multi-parameter coincidence spectrometer

Abstract

A multi-parameter coincidence spectrometer (MPCS) coupled to a 300 kV electron accelerator has been developed for the study of inelastic electron-atom scattering cross sections. As a first application, the spectrometer has employed three detectors: one Si(Li) electron detector at 45°, one Ge photon (x-ray) detector in the electron scattering plane at −45° and a second Ge photon (x-ray) detector at 90° to the scattering plane. The doubly differential cross section (DDCS) for K-shell ionization and the triply differential cross section (TDCS) for bremsstrahlung have been measured at 100 and 140 keV for targets of Cu, Ag and TbF3. The K-shell DDCS exhibit the increase in cross section at higher scattered electron energy seen in earlier work. The initial results at the two different photon angles suggest that there may be some angular dependence in the K x-ray emission angle observed which indicate that the data should be interpreted as triply differential in the K x-ray emission angle as well as the electron angle and energy. The TDCS for bremsstrahlung is in fair agreement with the Bethe-Heitler formula. While the present data do not extend to low enough scattered electron energy (high enough radiated photon energy) to be compared with the recent calculation of Shaffer and Pratt, it is hoped that further data will provide overlap for a few points and a test of the theoretical calculations. Future plans to measure the above cross sections at different angles and energies, as well as plans for new studies of double bremsstrahlung and triple coincidence processes with the new MPCS will be discussed.