会議発表用資料 Novel approaches for 90Sr analyses in contaminated environmental samples

Kavasi, Norbert  ,  Sahoo, Sarata  ,  Arae, Hideki  ,  Aono, Tatsuo

2016-02-25
内容記述
Introduction: Radioactive strontium isotopes are generated with high cumulative fission yield (5 6 %) during thermal neutron fission in a nuclear reactor. The physical half-life of 89Sr (50.52 d) is short but that of 90Sr (28.8 y) is long enough to generate radioecological repercussions1. 90Sr has a long lasting biological half-life (~18 y) in the human body, due to its chemical similarity to calcium the importance of 90Sr analysis is emphasized in case of a nuclear disaster. The world-wide spread of 90Sr, as a background, is derived from the global atmospheric fallout contributed by large-scale atmospheric nuclear weapons tests conducted from 19452,3. In case of local contamination, nuclear accidents are not the only source of 90Sr isotope, misconducted underground nuclear weapon tests, improper handling of by products of nuclear weapon production or normal operation of nuclear facilities (e.g. reprocessing plants) can be taken into account.Material and Methods: The sample analysis can be divided into three parts: sample preparation, strontium separation and detection of 90Sr. Sample preparation consists pretreatment and pre concentration of strontium. For strontium separations many procedures can be applied, such as selective precipitation, liquid liquid separation, extraction chromatography, ion-exchange, ion chromatography. The detection of 90Sr can be carried out using radiometric (gas ionization detector, Cherenkov counter, LSC, etc.) or mass spectrometric (ICP-MS, AMS, RIMS, TIMS, etc.) methods.Results and Discussion: In case of the radiometric detection method, significant spectrum interferences occur due to the continuous nature of the energy distribution of beta radiation. Therefore 90Sr from complex matrices has to be separated from other beta emitter nuclides, such as Th, Pb, Bi, Ra, K isotopes. In nuclear accidental situation, other disturbing nuclides should be considered since all of the fission products generated in nuclear reactors are beta emitters, such as Te, I, Cs, Ag, Ru, Ba isotopes. In case of the mass spectrometric method, the isobaric interferences (90Zr) and the limitation of the abundance sensitivity (peak tail of the natural occurring 88Sr with 82.6 % abundance) can cause problems.Comparing the two methods, the radiometric can perform a lower detection limit with elevated sample size (~10 g or more) and chemical consumption along with quite long measurement time (waiting time for the secular equilibrium between 90Sr and 90Y is two weaks). The mass spectrometric methods have high sample through put and low sample size requirement (1 g or lower). The main limitation is the abundance sensitivity; therefore the detection limit is influenced by the amount of the stable strontium concentration in the environmental samples. References:1Vajda, N. & Kim, C. K. Determination of radiostrontium isotopes: a review of analytical methodology. Appl. Radiat. Isot. 68, 2306-2326, (2010).2Energy, N. O. O. U. S. D. o. United States Nuclear Tests July 1945 through September 1992. (2000) http://www.nv.doe.gov/library/publications/historical/DOENV_209_REV15.pdf. (Accessed: 14th September 2015)3Mangano, J. J., Gould, J. M., Sternglass, E. J., Sherman, J. D. & McDonnell, W. An unexpected rise in strontium-90 in US deciduous teeth in the 1990s. Sci. Total Environ. 317, 37-51, (2003).
Convener, Steering Committee IARPIC-2016 Radiation Safety Division

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