A highly flexible, data intensive acquisition system for characterizing low-level decay events

Since the early 1970's, the National Institute of Standards and Technology (NIST) has maintained a low-level decay, multi-channel counting facility for measuring environmental samples and for pulse distribution studies tied to the behavior of proportional and Geiger-Muller detectors. Pulses have been time stamped and sorted using a hard-wired digital logic interface to discriminate coincidence, anticoincidence, guard and test pulse events; to digitize the pulse-height and rise-time; to monitor specific characteristics of intra-channel and inter-channel events; and to measure microsecond timing between any two events. To enhance event characterization, a computer-based waveform analyzer was added in 1985 to digitize individual pulses. In 2002, a next-generation low-level counting (NG-LLC) system was developed using commercial off-the-shelf electronics. The objective of this paper is to describe the key components of the NG-LLC system. Many of the event parameters previously determined by inflexible digital logic are now calculated in software.