Characteristics of amorphous selenium detector for monoenergetic X-ray determined by Monte Carlo simulation

Amorphous selenium (a-Se) has been proved to have excellent detective quantum efficiency, which suggests that a-Se would provide good image quality that is equivalent to or better than conventional film. We implemented a simulation model using Monte Carlo method to acquire the characteristics of detection material itself, not of whole detection system, to compare with conventional film or screen, and obtained PSF, LSF and MTF of photon absorption in α-Se relative to X-ray energy, thickness, and so on. First, we translated XCOM front Fortran into C++ language, which was needed to generate cross sections and attenuation coefficients to obtain path length and interaction type of photons. Using Monte Carlo simulation codes in Visual C++ incorporated with this program, total cross sections, attenuation coefficients, partial cross sections for incoherent and coherent scatterings, photoelectric absorption and pair production were obtained for photons with energy between 1keV and 100GeV. The Monte Carlo simulation codes developed in this study allowed the users to select a random number generator among four suggested ones in Numerical Recipes in C. Based on three interaction types occurring for photons in energy range of diagnostic X-ray (1-100keV), we estimated the position of interaction and the direction of scattered photons in α-Se. Via Fourier transformation of PSF and LSF, we obtained MTF. Density and thickness of a-Se detector was 4.26g/cm3 and 300 μm, respectively, and number of induced photons was 100,000. The percentage of absorbed photons in induced direction was 99.8% for 5keV and 86.4% in 30keV photons. Probability of interaction became higher for lower energy photon and in thicker a-Se.