Monte Carlo simulation of primary electron production inside an a-selenium detector for x-ray mammography: physics.

Selenium is among the materials under investigation that may form effective detectors and provide a major contribution to digital mammography. Till the final image formation, there is an intervention of the x-ray photons transformation to primary electrons and their subsequent ionizing drift towards the electrodes that collect them. The characteristics of the generated primary electrons inside a-Se material such as their angular, spatial and energy distribution affect the characteristics of the final image. A Monte Carlo based model has been developed that simulates the x-ray irradiation of an a-Se detector plate, including primary photon interactions (photoelectric absorption, coherent and incoherent scattering), as well as secondary ones, such as fluorescence (Kalpha, Kbeta) and emission of Auger electrons. The angular, spatial and energy distributions for the generated primary electrons inside a-Se have been produced for various mammographic x-ray spectra and their usefulness in designing and optimizing a detector made of a-Se for digital mammography is discussed.