X-ray interaction characteristic functions in semiconductor detectors

Secondary photons produced by x-ray interactions, such as scattered and fluorescent x-rays, can degrade the performance of semiconductor imaging detectors. In this article, we define characteristic functions describing the spatial-frequency-dependent absorbed energy and counting spectra for energy-integrating and single-photon counting detectors, respectively. We describe the characteristic function as a sum of contributions due to several x-ray interaction mechanisms. To obtain the characteristic function of a detector, we performed list-mode analysis on the Monte Carlo simulation results obtained for an impulsive x-ray excitation, hence discriminating x-ray interactions depositing energies over space. We apply this analysis to cadmium telluride detectors for wide ranges of energy and detector designs. The shape of characteristic functions is mostly governed by fluorescent x-ray interactions rather than scattered photons. The effects of x-ray energy, detector pitch, and threshold energy on the characteristic functions of single-photon counting are discussed.