X-ray and charged particle detection with CsI(Tl) layer coupled to a-Si:H photodiode layers

This paper reports on a compact real-time X-ray and charged particle imager with digitized position output built either by coupling a fast scintillator to a photodiode array or by forming one on a photodiode array directly. CsI(Tl) layers 100-1000 μm thick were evaporated on glass substrates from a crystal CsI(Tl). When coupled to a crystalline Si or amorphous silicon (a-Si:H) photodiode and exposed to calibrated X-ray pulses, their light yields and speed were found to be comparable to those of a crystal CsI(Tl). Single β particle detection was demonstrated with this combination. The light spread inside evaporated CsI(Tl) was suppressed by its columnar structure. Scintillation detection gives much larger signals than direct X-ray detection due to the increased energy deposition in the detector material. Fabrication of monolithic type X-ray sensors consisting of CsI + a-Si:H photodiodes is discussed