THE MEASUREMENT OF THE ISOTOPIC COMPOSITION OF PLUTONIUM IN AN IRISH-SEA SEDIMENT BY MASS-SPECTROMETRY

Samples from sediment cores, collected from a site close to the Sellaf ield outfall and dated using conventional gamma- and alpha-spectrometr y, have been analysed using Inductively Coupled Plasma Mass Spectromet ry (ICP-MS) and Thermal Ionisation Mass Spectrometry (TIMS). This has provided information on the isotopic composition of plutonium in the l iquid discharges from Sellafield; such information is not available us ing conventional cc-spectrometry alone. There was very good agreement between the Pu-240/Pu-239 ratios obtained by the two MS methods. More recent discharges have been characterised by a progressive decrease in the relative proportion of Pu-239.