Year
2012
Abstract
Plutonium measurements which use the common gamma-ray/passive neutron combination are highly sensitive to the presence of impurities, particularly (a,n) emitters, which can cause higher uncertainties and/or skewed mass results. Thus, the relatively short assay times afforded by passive measurements are offset by a loss in accuracy. Conversely, while a scheme which uses a combination of gamma ray and calorimetric measurements has been shown to give much higher accuracy than typical neutron measurement, the approximately 8+ hours required for calorimeter measurements makes this the least preferred method when high throughput is desired. The calorimeter-based known-a multiplicity analysis scheme was therefore developed as a means to combine the accuracy and precision of a calorimetric measurement with the relative speed of passive neutron counting. This method is uniquely suited to batch analysis, i.e. measurements of multiple plutonium items having a common source, since it only requires gamma-ray, neutron, and heat measurements of a representative sample from the batch. Using the a-value determined from this combination of measurements and assuming a homogeneous distribution of source material, other items in the batch can then be assayed with high accuracy using only a combination gamma/neutron measurement.