Monte Carlo modeling of electrophotographic x-ray detectors

Abstract

A Monte Carlo model for an electroradiographic detector is presented. It takes into consideration recombination as a loss factor inherent in the physics of the x-ray photon attenuation, but one whose importance decreases with increasing photon energy, owing to the increasing spatial dispersity of the hole-electron pairs, therewith. This treatment reasonably simulates both the applied field and the x-ray photon energy dependences observed experimentally for the apparent carrier pair production energy in amorphous Se and particulate, tetragonal PbO devices. An activation energy for free carrier generation in Se, despite the excess thermal energy with which the carriers are initially produced, is also required to make the model correspond with experiment in the Se case. Bonding theory suggests that this is an inevitable consequence of the disordered state of the amorphous radioconductor. Detective Quantum Efficiency estimates can be extracted from the Monte Carlo simulation. These data indicate that the primary loss factor in xeroradiographic detectors, from the standpoint of signal-to-noise ratio, is incomplete attenuation of the incident x-ray energy.