Error Propagation for Gamma Spectroscopy and Neutron Coincidence Counting for Plutonium-Bearing Materials

The error characteristics of both high-resolution gamma spectroscopy and high-level neutron coincidence (HLNC) measurements, separate or combined, are discussed as they apply to nondestructive analysis of plutonium-bearing materials. Expressions have been derived to estimate the overall variance in the ²⁴⁰Pu effective mass and in the total plutonium mass in terms of the specific contributions from uncertainties in the measurements, the pertinent physical variables (including isotopics and impurities), and the instrumental constants. Experimental data available in the published literature have been used to illustrate the error characteristics of the HLNC and the effects of isotopic error correlations associated with materials having different burnups.