A scan a source matrix correction technique for use with a reconfigurable passive neutron plutonium assay system

We have developed a mobile, reconfigurable plutonium assay system consisting of eight identical passive neutron counting modules that can be used individually or in combination, allowing almost any Pu-bearing container to be assayed. Each module consists of three 3He proportional counters embedded in a polyethylene moderator. The detectors are linked to a standard coincidence analyser, which measures the Totals countrate, the Reals plus Accidentals countrate and the Accidentals coincidence countrate. This paper describes the principal characteristics of the assay system and reports on a feasibility study aimed at developing a novel matrix compensation method for inhomogeneous matrices in drummed waste. The method consists of scanning a 252Cf source up the outside of the drums and relating the measured countrate to the detection efficiency for Pu within.