Comparison of Borehole Neutron Activation Systems for Direct Assay of Plutonium

Borehole neutron activation systems are capable of in situ plutonium assay at a 10 nCi Pu/g concentration. Two such systems, one based on a 252Cf neutron source (called CF) and one based on a 14-mV neutron generator (called N Gen), were field tested on the Hanford Site in 216-Z-1A actinide crib. Both systems produced a subsurface distribution for plutonium, and the distributions were within a few centimeters of each other at all depths. Converting the observed distribution to plutonium assay is difficult. Lack of a suitable calibration facility for subsurface plutonium precludes direct calibration of the systems. Theoretical calculations were made to determine plutonium based on past uranium calibration experience. The results were not consistent. The two systems and the field test will be compared. Initial studies and existing methods will be noted.