A part per trillion isotope ratio analysis of 90 Sr/ 88 Sr using energy-filtered thermal ionization mass spectrometry

Strontium-90 is a major radioactive nuclide released by nuclear accidents and discharge waste. Input of such radioactive nuclide into earth surface environment causes potential threat of long-term internal exposure when taken up by organism. Rapid and precise measurement of 90 Sr in variety of environmental sample is important to understand the distribution and dynamics of 90 Sr in the local environment after the accident and to assess the effect of radioactive nuclide inputs on bodies. However, previous 90 Sr measurement techniques have drawbacks such as long measurement times for radiometry and high detection limits for mass spectrometry. Here we present a technique to accurately measure a significantly small amount of 90 Sr in natural environmental samples using an energy-filtered thermal ionization mass spectrometry. Our technique achieved a 90 Sr detection limit of 0.23 ag, which corresponds to a 90 Sr activity of 1.2 µBq. The detection limit was lowered by two orders of magnitude compared with the previous mass spectrometric 90 Sr analyses. The ability of our technique will expand the applicability of mass spectrometric 90 Sr survey not only to the rapid 90 Sr survey upon nuclear accidents but also to study a long-term environmental diffusion of radioactive materials using size-limited environmental and biological samples.