Characteristics of CsI(Tl) scintillating detector based on solid state photo multiplier

SSPM is a multipixel silicon (solid state) photomultiplier. The outputs of all pixels are connected via load resistors to the common output of the device. Each pixel is a p—n junction, to which a reverse bias voltage in excess of the breakdown voltage (≪60V) is applied. Pixels operate in Geiger mode. The discharge ceases when the voltage across the pixel drops below the breakdown voltage owing to the presence of a load resistor placed in series with each pixel. The charge amplification coefficient of an individual pixel is ∼10⁶. Though each pixel operates as an independent Geiger element, the whole photomultiplier can function as an analog device, since the charge at its output depends on the total charge of all pixels triggered by a scintillation in the crystal. SSPMs with a total area of 1×1 mm² of 576 pixels with dimensions of ∼40μm was used. Detector is based on a CsI(Tl) single-crystal scintillator, since it is nonhygroscopic, has a high light yield and is easy to process. The scintillator has a nearly cylindrical shape with a diameter of 2 mm and a height of 5 mm. Detector have energy resolution for Cs-137 line less 10% at dose rate up to 30 R/h. The temperature tests showed that scintillation detectors with SSPMs are capable of making measurements over a wide temperature range (up to 52°C) with inessential distortions of recorded spectra. Second detector was made with SSPM_0710G9mm sensor. This SSPM has sensitive area 9.0mm² and number of microcells — 8100. The maximum QE at 580 nm equals 40%. This photosensor operates without external thermostabilizer (no cooling). The volume of scintillating crystal CsI(Tl) is 0.785cm³. In temperature range 52°C energy resolution of detector for 662 keV was changed from 10% to 11.4%, and noise threshold was moved from 12 keV to 74 keV.