Accurate measurement of 90Sr at Ultra trace levels in Environmental Samples using Thermal Ionization Mass Spectrometry

The 90Sr (T1/2 = 28.8 y) is a pure beta emitter radioisotope, produced by the fission of U and Pu isotopes. Low level (some Bq/kg or mBq/kg) 90Sr contamination exists in different environmental matrices as a result of nuclear weapon tests and nuclear accidents. The Sr element shows bio-chemically similarity to calcium, therefore the 90Sr isotope can incorporate into the human bone structure causing long-term radiation dose. Considering the public health and natural radiation protection, precise and accurate determination of 90Sr in various environmental, biological and radioactive waste samples is important.Radiometric methods have been mainly used for 90Sr analysis. However, significant developments on sample introduction, detector and interference removal techniques, many successful 90Sr determinations have been reported using mass spectrometry instruments. The main advantages of the mass spectrometry method over the radiometric are the shorter analysis time, higher sample throughput and smaller sample intake.In this work, a new 90Sr analysis method using Thermal Ionization Mass Spectrometry (TIMS) equipped with a Daly ion-counting system will be introduced. Detection of 0.2 fg (1 mBq) 90Sr was demonstrated with an excellent abundance sensitivity for the 90Sr/88Sr isotope ratio (2.1×10e-10). For method validation, certified reference material (wild berry-IRMM-426, 90Sr= 124±24 Bq/ /kg) and standard reference material (freshwater lake sediment-NIST-4354, 90Sr= 512±118 Bq/kg) were analysed.This new method was applied for the first time in the history of mass-spectrometry in a worldwide open proficiency test (IAEA-TEL 2017-3). The 90Sr was determined in tap water and milk powder samples and values were ‘accepted’ with both accuracy and precision.Fukushima 10 years: Forest, River, Ocean, and Foo