Age determination of plutonium using inductively coupled plasma mass spectrometry

The aim of this study was to develop a method for age determination of plutonium material based on chemical separation and the analysis of 241Pu and 241Am using inductively coupled plasma mass spectrometry. The method presented is well suited for age determination of plutonium material based on the 241Am/241Pu isotope amount ratio. A thorough separation of Pu and Am was achieved from the solid phase extraction procedure used, and the determined ages of the Pu materials corresponded well with the age reported by the reference material suppliers. Also the γ-spectrometric analyses of the two samples with higher concentrations showed a good agreement with the mass spectrometric determinations. The use of ICP-SFMS is advantageous due to its high sensitivity and relatively simple sample preparation. The utilisation of the 241Am/241Pu pair for age determination is valuable compared to using a Pu/U pair since contamination or mixing with U from other sources are of higher probability in most case compared to contamination from 241Am. However, a condition for this kind of age determination is that the daughter nuclide was not present in the material at t=0 or that this concentration is known. Thus, if this information is not available a more reliable dating can then be based on both the 241Am/241Pu and a Pu/U ratio. (LN)