Characterization of a γ-ray detection system based on a CsI(Tl) scintillator coupled to a silicon PiN diode

As a step towards the realization of a γ-ray 8x8 modular imaging probe, the single pixel element has been extensively tested. It consists of a 6.1 mm² x 3.7 mm CsI(Tl) scintillation crystal optically coupled to the backside of a 3.6 mm² PiN diode on a 300 um fully depleted silicon wafer. The γ-ray detection system has been irradiated with the radio-isotopes: ²⁴¹Am, ^99mTc, ¹⁵²Eu and ¹³⁷Cs to span the energy range between 60 and 1400 keV. The linearity of the response is very good and the total conversion efficiency is 0.45. The dependence of the energy resolution on the electronic noise has been simulated and compared with experimental values. The intrinsic resolution of the crystal is about 6% and the ENC about 200 rms electrons. The resolution on the 140 keV line of the ^99mTc and the 660 keV line of the ¹³⁷Cs are 19% and 7.4%, respectively.