Investigating the non-ideal behavior of the Amptek A111 charge sensitive preamplifier & discriminator board—3He proportional counter combination used in common safeguards neutron coincidence counters

Abstract

Neutron coincidence counting is a well-established technique used for the nondestructive quantification of special nuclear material during international safeguards inspections. The neutron counters are commonly designed with an annular body, centered about an inner well or cavity into which a measurement item is placed, and the moderating annulus is populated with 3He tubes connected to a varying number of preamplifiers. The Canberra Industries JAB-01 preamplifier/amplifier/discriminator board is employed within the company’s neutron coincidence counters, built for use by the International Atomic Energy Agency. Non-ideal behavior of these boards was identified during a detector characterization, using list mode data acquisition, of a Canberra Industries JCC-71 Neutron Coincidence Collar implementing four JAB-01 boards. List mode data acquisition and analysis reveals features that have commonly been overlooked by historic timing gate selection while using shift register data acquisition methods, which are routinely adopted in international safeguards. It has been shown that double pulsing effects are not fully captured within the predelay setting; therefore, they may influence the response of the system within the standard operating regime. We set out to identify and correct for double pulsing in our post analysis of neutron pulse trains, while isolating this behavior to the relevant system. To understand and potentially address these concerns, the responses of two different JAB-01 board systems – the JCC-71 Neutron Coincidence Collar and a modified JCC-51 Active Well Neutron Coincidence Counter – are compared with the responses of an AnTech Inc. N2071 Neutron Coincidence Collar that also uses an amplifier built on the Amptek A111 Charge Sensitive Preamplifier & Discriminator chip, and a JCC-71 that employs custom preamplifiers designed at Oak Ridge National Laboratory.