Resolution and noise properties of scintillator coated X-ray detectors

The imaging properties of X-ray pixel detectors depend on the quantum effic iency of X-rays, the generated signal of each X-ray photon and the distribu tion of the generated signal between pixels. In a scintillator coated devic e the signal is generated both by X-ray photons captured in the scintillato r and by X-ray photons captured directly in the semiconductor. The Signal-t o-Noise Ratio in the image is then a function of the number of photons capt ured in each of these processes and the yield, in terms of electron-hole pa irs produced in the semiconductor, of each process. The spatial resolution is primarily determined by the light spreading within the scintillator. In a pure semiconductor detector the signal is generated by one process only. The Signal-to-Noise Ratio in the image is proportional to the number of X-r ay photons captured within the sensitive layer. The spatial resolution is a ffected by the initial charge cloud generated in the semiconductor and any diffusion of carriers between the point of interaction and the readout elec trode. In this paper we discuss the theory underlying the imaging propertie s of scintillator coated X-ray imaging detectors. The model is verified by simulations using MCNP and by experimental results. The results from the tw o-layer detector are compared with those from a pure semiconductor X-ray de tector. (C) 2001 Elsevier Science B.V. All rights reserved.