Diode laser based resonance ionization mass spectrometric measurement of strontium-90

A diode laser based scheme for the isotopically selective excitation and ionization of strontium is presented. The double-resonance excitation 5s21S0 → 5s5p 3P1 → 5s6s 3S1 is followed by photoionization at 488 nm. The isotope shifts and hyperfine structure in the resonance transitions have been accurately measured for the stable isotopes and 90Sr, with the measurement of the 90Sr shifts using sub-pg samples. Analytical tests, using graphite crucible atomizaiton, demonstrated 90Sr detection limits of 0.8 fg and overall (optical + mass spectrometer) isotopic selectivity of > 1010 against stable strontium. (author)