A DEADTIME REDUCTION CIRCUIT FOR THERMAL NEUTRON COINCIDENCE COUNTERS WITH AMPTEK PREAMPLIFIERS*

We have developed a deadtime reduction circuit for thermal neutron coincidence counters using Amptek preamplifier/amplifier/discriminator circuits. The principle is to remove the overlap between the output pulses from the Amptek circuits by adding a derandomizer between the Amptek circuits and the shift-register coincidence electronics. We implemented the derandomizer as an Actel programmable logic array; the derandomizer board is small and can be mounted in the high-voltage junction box with the Amptek circuits, if desired. Up to 32 Amptek circuits can be used with one derandomizer. The derandomizer has seven outputs: four groups of eight inputs, two groups of 16 inputs, and one group of 32 inputs. We selected these groupings to facilitate detector ringratio measureme..;;. The circuit was tested with the five-ring research multiplicity counter, which has five output signals—one for each ring. The counter's deadtime was reduced from 70 to 30 ns.