NDA technique for the assay of wet plutonium oxalate

A method has been developed to quantitatively measure batches of wet plutonium oxalate. The method is based on a count of coincidence neutrons to which a correction is applied for the effects of neutron moderation by water. A therma-neutron coincidence counter (TNC) with two concentric rings of /sup 3/He detectors provides the signal needed for the water correction. The signal is the ratio of neutron counts between the detector rings that changes with the percent of water in plutonium oxalate. To evaluate the measurement technique, 26 batches of plutonium oxalate were measured in an in-line TNC. The evaluation showed the measurements to be essentially unbiased and precise to 2.2%.