On the angular dependence of Bremsstrahlung x-ray emission

Abstract

The angular probability distribution of x-rays from a single interaction of a high energy electron with a target atom is a function of the incident-electron energy, direction and target material. This distribution can be quite directional, which suggests that x-ray tube efficiency might be increased if this effect was used. This can be important for novel tubes that use scanning electron beams or carbon nanotubes that have low output flux. We performed Monte Carlo(MC) simulations for studying how this angular distribution is affected by the interactions in thick targets. The theoretical distribution for single-atom interaction was verified using a 4nm tungsten (W) sphere. Contributions of the various processes undergone by the electrons and x-ray photons were analyzed individually. The angular distributions of x-rays generated by electrons incident normally and at a grazing angle to a 4mm thick target were calculated. The results for a 12μm transmission target were also simulated. For single interactions, the theoretical peak for 120keV electron at 28° was measured to be 29° for the MC simulations. The transmission target was found to have 26% higher x-ray output in the forward direction compared to a conventional tube for E≥30keV. When x-ray flux per unit heat was considered for E≥30, grazing incidence of electrons and the associated reflection beam was found to be 41% more efficient than a conventional tube.