Resonance ionization spectroscopy of stable strontium isotopes and Sr-90 via 5s(2) S-1(0) -> 5s5p P-1(1) -> 5s5d D-1(2) -> 5s11f F-1(3) -> Sr+

Single-, double- and triple-resonance ionization in the 5s(21)S(0) --> 5s5p P-1(1) --> 5s5d D-1(2) --> 5s11f F-1(3) --> S-r+ system of strontium was i nvestigated to achieve an efficient and highly selective ionization scheme for ultra-trace detection of the radioisotope Sr-90. Isotope shifts and hyp erfine structure for all stable isotopes of Sr were measured in all three r esonant transitions. Good agreement with previous data was found in the 5s( 21)S(0) --> 5s5p P-1(1) transition and precision was improved by approximat ely one order of magnitude. Isotope shifts, including that for Sr-90, and h yperfine structure in the two- and three-photon transitions were measured f or the first time. The double- and triple-resonance schemes were characteri zed with respect to their isotopic selectivity for detection of Sr-90. The double-resonance process offers an optical selectivity of 2 x 10(4), while unfavorable isotope shifts in the triple-resonance process limit its select ivity to similar to 100. Using double-resonance ionization combined with ma ss spectrometric detection, an overall detection efficiency of > 10(-5), a selectivity > 10(10), and a detection limit of 0.7 fg Sr-90 in samples with a 10(10) excess of stable Sr isotopes have been demonstrated. (C) 2000 Els evier Science B.V. All rights reserved.