Standard Test Method for Nondestructive Assay of Plutonium by Passive Neutron Multiplicity Counting

1.1 This test method describes the nondestructive assay of plutonium in forms such as metal, oxide, scrap, residue, or waste using passive neutron multiplicity counting. This test method provides rapid results that are usually more accurate than conventional neutron coincidence counting. The method can be applied to a large variety of plutonium items in various geometries in cans, 208-L drums, or 1900-L Standard Waste Boxes. It has been used to assay items whose plutonium content ranges from 1 g to 1000's of g.

1.2 There are several electronics or mathematical approaches available for multiplicity analysis, including the shift register, the Euratom Time Correlation Analyzer, and the List Mode Module, as described briefly in Ref. (1).

1.3 This test method is primarily intended to address the assay of ²⁴⁰Pu-effective by moments-based multiplicity analysis using shift register electronics (1,2 ) and high efficiency neutron counters specifically designed for multiplicity analysis. This test method requires knowledge of the relative abundances of the plutonium isotopes to determine the total plutonium mass.

1.4 This test method may also be applied to modified neutron coincidence counters which were not specifically designed as multiplicity counters, with a corresponding degradation of results.