Analytical determination of radioactive strontium and cesium by Thermal Ionization Mass Spectrometry

Thermal Ionization Mass Spectrometry (TIMS) has been evaluated for the detection of the radioactive isotopes of Sr and Cs. The commercial instrument (i.e., a Thermo Scientific Triton) was investigated for the analysis of isotopic ratios of Sr-89/Sr-90 and Cs-135/Cs-137 in the presence of atomic isobars (Y-89 and Zr-90 for Sr-89,Sr-90 analysis and Ba-135,Ba-137 for Cs-135,Cs-137 analysis). The decontamination achievable instrumentally was examined by isotopic ratio measurements of Y-89/Sr-88 and Zr-90/Sr-88 for Sr and Ba-135/Cs-133 and Ba-137/Cs-133 for Cs. The decontamination found was at or above 2.0E+8 for Zr-90 from Sr-88, while the Y demonstrated a temperature dependence as it sublimed from the filament but remained better than approximate to 5E+7. The decontamination of Ba from Cs did not show any temperature dependence and remained above 5E+6 and 8E+6 for Ba-135 and Ba-137 from Cs-133, respectively. Two standard fusion procedures one with sodium hydroxide (NaOH) plus sodium peroxide (Na2O2) flux, and the second used lithium tetraborate (Li2B4O7) plus lithium metaborate (LiBO2) flux were evaluated for preparation of sample matrices prior to performing chemical separations. Ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) and Sr-spec resin were used to isolate the Cs and Sr, respectively from a prepared background matrix (i.e., Montana Soil). A graded approach, increasing in stable background isotopes, was performed to monitor the chemical and instrumental response. The radioisotopes of Sr and Cs were produced by thermal neutron irradiation of a highly enriched uranium foil. Even though the irradiated sample was not a certified standard it does provide accurate expectation values via the published cumulative fission yield nuclear data in the Evaluated Nuclear Data Files (ENDF) [1]. The intra-element isotopic ratio results presented in this work for Sr-89/Sr-90 and Cs-135/Cs-137 agree with the published data at 1 sigma. Furthermore, the uncertainty of the isotopic ratio measurements with TIMS was a factor of 5-10 improved compared to these published values. (C) 2019 Elsevier B.V. All rights reserved.