Spectroscopic analysis of radioactive strontium with low isotopic abundance using laser resonance ionization

Strontium-90 (90Sr, half-life of 28.8 years) is one of the major fission products released in the Fukushima Daiichi Nuclear Power Plant accident in Japan. Due to the high concentrations of Sr stable isotopes in marine products, an upper limit for 90Sr isotopic abundance in them is of the order of 1 ppb or less. Resonance ionization technique using narrow linewidth lasers is suitable for analysis requiring high elemental and isotopic selectivity. In this study, we have investigated on 689.4 nm - 487.4 nm - 393.8 nm three-step resonance ionization of Sr atoms, where the 90Sr isotope shifts in the second and third transitions were predicted using a King plot approach to evaluate the optical isotopic selectivity. As the first step in measuring real samples, the influence of coexisting elements in seawater was also derived.