Photon and primary electron arithmetics in photoconductors for digital mammography: Monte Carlo simulation studies

Abstract

Materials like CdTe, CdZnTe, Cd 0.8 Zn 0.2 Te and ZnTe are suitable photoconductors for direct conversion digital flat panel x-ray image detectors. The x-ray induced primary electrons inside photoconductor's bulk comprise the initial signal that propagates and forms the final signal (image) on detector's electrodes. An already developed Monte Carlo model that simulates the primary electron generation in photoconducting materials, such as those mentioned above, has been used to study the arithmetics of fluorescent photons, escaping photons and primary electrons in these materials in the mammographic energy range. In this way insights are gained concerning the primitive stage of signal formation that lead to the investigation of the factors that affect the primary electron generation. It was found that for the typical photoconductor thicknesses (300-1000 µm): (i) in all materials and incident energies the escaping of primary photons is negligible and does not influence the number of primary electrons, (ii) the overwhelming majority of escaping photons is backwards escaping fluorescent photons, (iii) the number of primary electrons increases at energies higher than Cd and Te K-edges where the fluorescent photon escaping decreases and their absorption is followed by long atomic deexcitation cascades and (iv) ZnTe has the maximum number of primary electrons produced for energies between 16 and 26 keV while CdTe for higher energies. KEYWORDS: Materials for solid-state detectors; Detector modelling and simulations I (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc); X-ray radiography and digital radiography (DR)

A Monte Carlo study of primary electron production inside photoconductors for digital mammography and indications of material suitability

“…According to the analysis made in the current paper as well as in [5], the number of primary electrons does not significantly change in a particular zone. Therefore, the relative average numbers It is seen that in Zone A, in contrast to the rest of zones, the percentages are all above 86%.…”

“…Using this model, the energy, angular and spatial distributions of 2010 JINST 5 P08004 primary electrons have been studied. For the case of CdTe, CdZnTe, Cd 0.8 Zn 0.2 Te and ZnTe, an investigation was also made concerning the dependence of the primary electron production on the incident x-ray energy [5]. In this paper, this investigation has been extended to include the rest of the photoconducting materials.…”