A High Rate NaI Detector System

Front end electronics (detector to ADC) have been developed to operate over an input count rate range of 105 to 106 counts per second with less than ± 1% gain shift and minimal resolution degradation. The system was developed to satisfy requirements for a nuclear hardened gamma densitometer utilizing multichannel analyzer pulse height analysis techniques for reactor background subtraction. The circuitry developed includes a fast current mode preamplifier with first order count rate dependent gain compensation, a baseline restorer, a single channel analyzer with pile-up rejection and live time measuring circuits, and a fast linear gate. The single channel analyzer is used for energy region of interest selection so that only those pulses within the energy region of interest are presented to the analog to digital converter.