A theoretical study of the isotope selective excitation of La-138 from D-2(3/2,5/2) states

Isotope ratio enhancement factors and isotopic selectivities for La-138 in a natural abundance lanthanum sample as well as an enriched sample have been computed theoretically for the 5d6s(2) D-2(3/2)-5d(2)6p F-2(5/2)0 (593.068 nm), 5d6s(2) D-2(5/2)-5d(2)6p F-2(7/2)0 (593.062 nm), 5d6s(2) D-2(3/2)-5d(2)6p D-2(3/2)0 (550.134 nm), 5d6s(2) D-2(5/2)-5d(2)6p D-2(5/2)0 (545.514 nm) and 5d6s(2) D-2(3/2)-5d6s6p F-4(3/2)0 (753.923 nm) transitions for narrow band laser excitation in a one-photon resonant two-photon ionisation scheme considering a Lorentzian atomic profile for simulation of the excitation spectrum. Simulations have been carried out for a laser bandwidth of 50 MHz. The coherence effects are ignored in the computation as the laser bandwidth (50 MHz) is much smaller than the largest separation between the hyperfine levels (i.e. gamma(L) << Delta(HFS)). The results obtained for the D-2(5/2)-D-2(5/2)0 (545.514 nm) transition are about 19% higher than the D-2(3/2)-F-4(3/2)0 (753.923 nm) transition used by Young et al. This increased isotopic selectivity can be used for isotope selective excitation of La-138 with improved detection sensitivity. This method demonstrates its usefulness in identifying the most efficient lines in order to focus experimental effort on these transitions. (C) 1997 Elsevier Science B.V.