Title: Analizne Metode Za Dolocanje Izotopskih Razmerij Uranovih In Plutonijevih Radioizotopov
Authors: JAKOPIC Rozle
Publisher: University of Ljubljana
Publication Year: 2008
JRC N°: JRC49605
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC49605
Type: PhD Theses
Abstract: Due to increased energy production by nuclear reactors, reprocessing and waste disposal, precise and rapid analysis of uranium and plutonium radioisotopes in various environmental samples is very important. The analysis of plutonium and uranium in various samples is complex, tedious and requires radiochemical separation prior to measurement. Two different procedures using anion exchange and TEVA, U/TEVA and TRU extraction columns were tested in this work and a good agreement was obtained. For the determination of 238Pu, 239+240Pu, 234U, 235U and 238U, alpha spectrometry was used. The recovery of the separation was determined using tracers. Thin sources for alpha spectrometry measurements were prepared by micro-precipitation of NdF3 or by electrodeposition. The evaluation of the measurement uncertainty was done with a spreadsheet method. For the determination of 241 Pu liquid scintillation counting (LSC) was used. After the radiochemical separation the samples were first measured using an alpha spectrometer. Then a part of the same filter was dissolved in a suitable scintillation cocktail and measured by LSC. The beta counting efficiency was determined using 3H and was 41.6%. another part of the filter was used for 240Pu/239Pu isotope ratio measurement by accelerator mass spectrometry (AMS). A combination of alpha spectrometry, LSC and AMS allowed the determination of the whole "spectra" of plutonium radioisotopes in the same sample. Thermal Ionization Mass Spectrometry (TIMS) was used for 240Pu/239Pu, 241Pu/239Pu and 242Pu/239Pu isotope ratio measurements. A new sample preparation procedure was developed, which employed the carburization of rhenium (Re) filaments. In this way, the ionization efficiency of the sample was improved significantly. A new "multi-dynamic" measurement technique was developed for isotope ratio measurements using the "multiple ion counting" (MIC) system. This technique was further combined with the filament carburization and applied to the NBL-137 isotopic standard and samples of the NUSIMEP 5 inter-laboratory comparison campaign. The results showed an improved precision and accuracy, compared to measurements carried out either in peak-jumping mode using one single ion counter (SEM) or in static mode using the MIC system with non-carburized filaments.
JRC Institute:Institute for Reference Materials and Measurements

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