X-ray-induced electron emission from metals

Energy and angular distributions of electrons (energies greater than 5 keV) emitted from metals irradiated by photons in the x-ray energy range were measured with a lithium-drifted silicon detector. The data presented here characterize electron emission distributions for normal photon incidence. They provide a systematic set of absolute distributions for quantitative comparisons to theoretical treatments of the combined photon and electron transport process. X-ray bremsstrahlung spectra with mean photon energies of 30 and 54 keV were used to induce electron emission from aluminum, copper, silver, and tantalum. Angular distributions for the higher-Z materials are found to be nearly cosine distributions in both the forward and backward emission directions, while the distributions for lower-Z materials deviate from a cosine distribution, tending to be more isotropic. Energy distributions are observed to change very little as a function of emission angle. Energy and angular distributions calculated by Monte Carlo and analytic techniques show good correlation with the measured distributions. Calculated forward and back (2π) emission efficiencies agree with experimental values within the uncertainties of these quantities (plus-or-minus15 to 20%). The generally good agreement between the experimental and theoretical results establishes the validity of the present techniques for calculating high-energy (greater than 5 keV) x-ray-induced electron emission from metals