A signal processor for high counting rate gamma ray spectroscopy with NaI(Tl) detectors

A high-counting-rate signal processor for prompt gamma neutron activation analysis (PGNAA) using NaI(Tl) detectors is described. The specific application is a very-low-rate, high-energy gamma ray in the presence of a high rate at lower energies, producing pile-up at the energy of interest. Several methods for improving counting-rate performance, such as shortening of the detector signal, baseline inspection, pile-up rejection and filtering, have been investigated and implemented. Experimental evaluation shows that the processor allows up to 400000 counts per second without significant distortion of the spectrum due to pile-up and with a minimum degradation of resolution. Through the use of an effective pulse-width-sensitive pile-up rejector, the pile-up effect has been further reduced by a factor of three, while rejecting less than 10% of valid counts. High data through put makes the processor applicable to online process control.<>