Modelling the response of a CsI(Tl)-PiN photodiode Microscintillator detector

The full instrument response of a superminiaturised CsI(Tl)-PiN photodiode radioactivity detector, intended for deployment on a meteorological radiosonde, has been modelled by combining a physics-based model of the sensor with the detector circuit response, obtained via an LTspice simulation. The model uses the incident energy of a gamma ray as an input, and produces the pulse expected from the detector. The detector response was verified by comparing the simulated energy calibration with a laboratory source. The measurement circuit is found to control the minimum detectable energy of 26 keV, and the maximum detectable energy is similar to 10 MeV. The energy sensitivity of the PiN detector is 0.29 +/- 0.02 mV/keV in the 0-800 keV range. The simulation and laboratory calibrations were consistent to better than 5% over the calibration range of the instrument.