Passive Neutron Waste-Drum Assay with Improved Accuracy and Sensitivity for Plutonium Using the Add-a-Source Method

Techniques have been developed to improve the accuracy and sensitivity for the nondestructive measurement ofplutonium in scrap and waste containers. The 200-L-drum assay system is based on the classical nondestructive assay method of passive neutron coincidence counting to determine theplutonium, but has added the new feature of to improve the accuracy of matrix corrections and has added statistical techniques to improve the low-level detectability limits. The errors introduced from matrix materials in 200-L drums have been reduced by one order of magnitude by using the add-a-source technique. The statistical filters to reduce the cosmic-ray spoliation neutrons have decreased the coincidence neutron background by approximately a factor of 2. 252Cf "add-a-source "