A compact back-end module for high-rate multielement X-ray spectrometers and γ-ray imagers

A compact single-ADC back-end module for the derandomization, acquisition and memorization of 16 spectra from high-rate multielement radiation detectors has been designed and characterized. The input signals, as provided by external peak stretchers, feed sample and hold circuits operated independently, which makes it possible to capture randomly-occurring events even in the worst case of time coincidences in different detection elements. The stored signals are then passed along synchronously to a common 12-bit 10 MHz flash ADC, by means of a switch array operated as a multiplexer. This provides derandomization of the arrival times of the events. A maximum count rate of about 500 kcounts/s/channel is featured. A homogeneous processing rate among the channels is guaranteed by driving the switches with an “intelligent” digital circuitry implemented in two programmable-logic units. Sliding-scale correction is used to reduce by two order of magnitudes the ADC native differential nonlinearity, and so to meet the requirements of the spectroscopic applications. The measured pulser-peak noise is 1.5 bins r.m.s. over a full scale of ~4000 bins