Isotope correlations for determining the isotopic composition of plutonium

Improved correlations using the Pu-238/(Pu-239 + Pu-240) alpha activity ratios determined alpha spectrometrically and the different atom ratios viz.Pu-240/Pu-239, Pu-241/Pu-239 and Pu-242/Pu-239 determined mass spectrometrically are presented for Pu produced in Pressurised Heavy Water Reactors (PHWRs). These correlations are useful to obtain the different atom ratios, with reasonable accuracy (1 to 10% depending upon the atom ratio), using only the Pu-238/(Pu-239 + Pu-240) alpha activity ratio determined alpha spectrometrically from a plutonium sample purified from Am-241. Since the correlations involve the relative values and not the absolute values of the atom% abundance of any specific isotope, the accuracy of the data obtained using these correlations is much better. In addition, the change in the atom% abundance of Pu-241 due to the relatively short half-life of Pu-241 (14.4 yr) does not create any ambiguity in the ratio Pu-242/Pu-239 and hence the accuracy of data for Pu-242 is not affected by the uncertainty in the data for Pu-241.