Isotope correlations for determining the isotopic composition of plutonium

Abstract

Improved correlations using the 238Pu/(239Pu + 240Pu) alpha activity ratios determined alpha spectrometrically and the different atom ratios viz. 240Pu/239Pu, 241Pu/239Pu and 242Pu/239Pu 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 238Pu/(239Pu+240Pu) alpha activity ratio determined alpha spectrometrically from a plutonium sample purified from 241Am. 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 241Pu due to the relatively short half-life of 241Pu (14.4 yr) does not create any ambiguity in the ratio 242Pu/239Pu and hence the accuracy of data for 242Pu is not affected by the uncertainty in the data for 241Pu.