Soft gamma-ray detector using CdWO4/ZnWO4 crystal with avalanche photodiodes

Cadmium tungsten (CdWO₄:CWO) and zinc tungsten (ZnWO₄:ZWO) crystals are promising materials for soft gamma-ray detectors because of their large atomic numbers and high densities, which give a high detection efficiency for gamma-rays. In this paper, we evaluated the capabilities of the two crystals, in terms of energy resolution and temperature dependence, as soft gamma-ray detectors using avalanche photodiode (APD). We first confirmed that the energy resolution measured with photomultiplier tube (PMT) was 7.0±0.1% and 5.8±0.1% at 662 keV for CWO and ZWO respectively. Next, we evaluated performance of the two crystals readout with APD varying temperature and shaping time. The best energy resolutions were obtained at -30°C with a shaping time of 20 μs, and their values were found to be 6.4±0.1% at 662 keV for both crystals. These are the best energy resolutions for the two crystals as far as we know.