Impact of temperature variation on the energy resolution of 3D position sensitive CZT gamma- ray spectrometers

Prototype 3D position sensitive CZT gamma spectrometers have been developed using 10x10x10 mm3 pixellated CZT detectors and a RENA-3 readout system from NOVA R&D. Under stable room temperature, excellent energy resolution of ~1% FWHM at 662 keV is consistently demonstrated for single interaction events in the detector with one time pre-measurement calibration. To test the feasibility of using the 3D CZT spectrometers for outdoor applications where ambient temperature is subject to a wide range of variation, the energy resolution performance of two detectors, one from Redlen Technologies and one from Yinnel Tech Inc., has been evaluated over the ambient temperature range from -5 to 45degC. The temperature related contributors to energy resolution, such as the readout electronics response and electron trapping in CZT detectors, have been investigated. The Redlen detector shows good stability in electron trapping with typical (mutau)_e (electron mobility-lifetime product) of ~1.5e-2 cm²/V, but a temperature- related gain drift up to +/-0.8% is observed with contribution from readout electronics. The Yinnel Tech detector has a typical (mutau)_e of ~5e-3 cm²/V at room temperature and shows significantly reduced (mutau)_e and increased electron trapping at lower temperatures. These results indicate both detectors need temperature related multiple calibrations to avoid significant energy resolution degradation from varying ambient temperature. With multiple 3D detector response calibrations at different temperatures, energy resolution close to ~1% FWHM at 662 keV can be maintained for both detectors.