Correlation Effects in Uncertainty Calculations Involving Atom (or Weight) Percent Isotopic Abundances

摘要

Isotope abundance ratios are the measured quantities (measurands) using mass spectrometer instruments Performance of the mass spectrometer instruments are monitored and controlled using limits established by analyzing well characterized certified reference materials (CRMs) traceable to the international system of units (S I). For a large number of uranium and plutonium isotopic CRMs available from the New Brunswick Laboratory (NBL), the certificates provide the isotopic composition expressed as atom percent or weight percent abundances For nuclear Material Control and Accountability (MC&A) as well as for cnticality safety evaluations, weight percent abundances of isotopes are often used The calculation of these derived quantities - weight percent (or atom percent) abundances - from the measured isotopic ratios is rather straight forward. In an estimation of the uncertainties of the atom percent or weight percent abundances from the isotopic ratios, correlation plays an important role The correlation effect in isotopic ratios is illustrated using the certified isotope ratios, atom percent abundances, and weight percent abundances of IRMM 3636.