Fig. 13.

Cross-sectional illustration of a ‘hybrid–flat-panel detector system under development shows the CsI scintillator to convert X-rays to light, an optical coupling medium to efficiently transfer light from the CsI to a thin a-Se ‘avalanche–detector under a high voltage. Light photons create electron-hole pairs, and as the holes accelerate to the negative electrode under high voltage, more ion pairs are created and are collected at the collection electrode. The amplification gain (1 to about 1,000) is controlled by the applied voltage (adapted from Zhao et al. [16])