Studies On The Determination Of Traces Of Uranium, Thorium, Neptunium And Plutonium In Environmental Samples By Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

Small amounts of radioactive materials are lost inevitably to the environment during any processing of nuclear material. With the development of nuclear power industry the corresponding waste has been grown. In order to evaluate the radioactive waste, which could affect the environment, and to devise projects for the nuclear waste disposal, the behaviour of long-lived artificial radionuclides in the environment are subject to detailed studies and are of increasing concern to environmental researchers. By analyzing radionuclides such as uranium. neptunium and plutonium in environmental samples, which were collected in the immediate environment of a nuclear process or nuclear site, researchers can detect evidence of the corresponding nuclear activities. Results from such research can also supply reliable information to assure the public safety and protect the environment.The concentration of neptunium and plutonium is extremely low in environmental samples. Additionally such samples have a complex matrix composition, which is to be taken into account for a proper analysis. Conventional radiochemical methods such as alpha spectrometry, neutron activation analysis, liquid scintillation system, fission track and gamma spectrometry for the quantitative determination of neptunium and plutonium often require complicated and time-consuming sample preparation and separation procedures. Due to the large amount of the complex and often unknown matrix, the analysis may also be covered by naturally occurring radionuclides.With the development of new analysis techniques, non-radioactive methods are increasingly used for the determination of trace or ultratrace radionuclides hi environmental samples. Inductively coupled plasma mass spectrometry (ICP-MS) has some advantages, such as high sensitivity, low detection limits, short analysis time, less chemical interferences and multi-elemental capability. Since 1980s, ICP-MS has been used overseas for the determination of uranium, thorium, neptunium, and plutonium in environmental samples. ICP-MS is one of the most suitable analysis techniques for the measurement of the long-lived radionuclides. However, ICP-MS is susceptible to spectral interference and non-spectral interference ormatrix effects. Therefore the set up of a simple, fast separation procedure is the key to success when traces of radionuclides are measured by ICP-MS. The main topics of research presented in this paper are as follows (points 1 to 6):(1) A microwave acid-digestion - ICP-MS method was established for the direct determination of U and Th in soil samples:A microwave acid-digestion method, which is characterised by faster digestion and smaller reagent consumption than traditional approaches for the dissolution of soil samples has been developed. The matrix effects of soil have been effectively corrected by using 209Bi as an internal standard. The memory effect during aspiration of the liquid sample into the ICP-MS has been eliminated by using 2% (v/v) HNOs. The results obtained from soil standards of IAEA are in good agreement with recommended values. This method was applied to four real soil samples. The results show a standard precision of below 10%.(2) Studies on the method of determination of uranium isotopes ratios in environmental samples:An efficient separation procedure for uranium from environmental samples by TOPO chromatographic extraction has been developed. The procedure has been optimized experimentally for the size of the column, different concentrations of nitric acid for column load, column rinse and the different types of eluent. Uranium was recovered with approximately 98% efficiency by the improved and optimized procedure. The decontamination factors for the soil matrix is approximately 1.4 x 103 up to 1.8 x 105.The instrumental mass bias is usually calculated from the analysis of reference materials with certified isotope abundance ratios. For both scan and jump mode the isotope discrimination correction was evaluated and the accuracy was compared. The results s...