Methods used at CNEN for the analysis of Pu and 241Am in marine samples

Very low levels of plutonium (sup(239,240)Pu and 238Pu) in marine samples (sea water, sediments, marine organisms) are determined by extraction chromatography with tri-n-octyl phosphine oxide (TOPO) supported on microporous polyethylene, electrodeposition and α-spectrometry. 236Pu or 242Pu is added as the yield detector and a high-resolution α-spectrometer is used for counting. The final recoveries are 62.6%+-9.7(sigma) for sea water, 45.4%+-9.6(sigma) for sediments and 81.7%+-4.5(sigma) for marine organisms. The method enables sup(239,240)Pu and 238Pu to be detected at the femtocurie level. A method proposed for americium analysis in 50g sediments is also described. After leaching of the samples, uranium, plutonium and thorium are extracted with TOPO, leaving americium, curium, lanthanides and iron in the aqueous phase. The organic phase is processed for plutonium, while in the aqueous solution separation of transplutonium elements from iron is obtained by a double oxalate co-precipitation. The decontamination of americium from the other transuranics is improved by extraction chromatography with di-2-ethylhexyl phosphoric acid (HDEHP). The final separation from lanthanides is obtained by a double anion-exchange step in thiocyanate media. Americium is electroplated and counted by α-spectrometry. The recovery ranges between 25 and 35%. (author)