CdTe linear arrays for registration of hard gamma-ray fluxes

Abstract

Two linear arrays were designed and fabricated for passive gamma emission tomography of spent fuel rod assemblies in the water pools of nuclear power plants. Each linear array comprised 104 CdTe detectors equipped with signal processing ASICs. Both were placed in tungsten alloy shields with multi-slit collimators. The CdTe detectors had simple metal–semiconductor–metal structure with platinum contacts and crystal dimensions 10×5×2 mm 3. Platinum contacts were deposited on the opposite surfaces of the detector elements having dimensions 10×5 mm 2; so the detector thickness was 2 mm. To increase the detection efficiency of high-energy gamma rays, the 5×2 mm 2 detector edges were irradiated with the gamma rays to allow the full 10 mm of CdTe to be used as the detecting medium. Out of the total of 250 CdTe detectors manufactured, 208 were selected to be installed into a pair of detector arrays (104 detector elements in each array). Preliminary selection of the detectors was made at room temperature based on the values of their leakage current and energy resolution by energies of 122 and 662 keV. Energy resolution of the detectors for 122 keV ranged from 9.5 to 10.6 keV; for 622 keV the resolution ranged from 17.8 to 22 keV. Fabricated linear arrays were tested under laboratory conditions with a Cs-137 source with an activity of 3.46 mCi. The results of linear arrays calibration are presented. Polarization effects in CdTe detectors were not observed during the tests.