Escape-reabsorption effect in scintillation detectors with photodiode readout

Escape of characteristic X-rays of energy Ex from the detector material following photoelectric effects when detecting X- or γ-rays of energy E0 results in a satellite peak displaced by Ex from E0. This phenomenon is common to scintillation (SC) detectors with PMT readout, as well. Using photodiode (PD), itself being sensitive to ionizing radiation, instead of PMT, another interaction can also take place: a reabsorption of escaping X-rays in the PD. This effect is pronounced in thin SCs, where the escape-to-photopeak ratio is high. A preliminary experiment with a CsI(Tl) SC coupled to a same size Si pn PD clearly showed the effect. An accurate determination of the energy shift of I and Cs Kα,β lines was, however, impossible. (K.A.)