Application of microprecipitation on membrane filters for Alpha Spectrometry, liquid scintillation counting and Mass Spectrometric determination of plutonium isotopes

For the determination of plutonium isotopes in environmental samples, chemical separation of plutonium together with a suitable sample preparation method for measurement is necessary. In this work, a combined method for the determination of 238Pu, 239Pu, 240Pu and 241Pu based on alpha spectrometry, Liquid Scintillation Counting (LSC) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is presented. For the alpha spectrometric determination of 238Pu and 239(40)Pu, sample preparation by coprecipitation of Pu with NdF3 on a membrane filter after separation by anion exchange, using 242Pu as tracer, is widely used. This sample preparation method was also applied as a preconcentration step for the determination of 240Pu/239Pu ICP-MS after wet ashing of a part of the membrane filter. 241Pu was measured with LSC after dissolving a part of the same membrane filter in a suitable cocktail and using the total alpha activity of the filter for determination of the chemical yield. The use of this approach gives the advantage of combining the strengths of both radiometric and mass spectrometric methods for plutonium determination after chemical separation from environmental samples. Results from the measurement of reference materials and from sediment samples from the Irish Sea are presented and the applied methods are compared with respect to their detection limits for the investigated nuclides.