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 Sellafield outfall and dated using conventional γ- and α-spectrometry, have been analysed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Thermal Ionisation Mass Spectrometry (TIMS). This has provided information on the isotopic composition of plutonium in the liquid discharges from Sellafield; such information is not available using conventional α-spectrometry alone. There was very good agreement between the240Pu/239Pu ratios obtained by the two MS methods. More recent discharges have been characterised by a progressive decrease in the relative proportion of239Pu.