Isotope ratio analysis on micron-sized particles in complex matrices by Laser Ablation-Absorption Ratio Spectrometry

Laser ablation has been combined with dual tunable diode laser absorption spectrometry to measure Gd-152:Gd-160 isotope ratios in micron-size particles. The diode lasers are tuned to specific isotopes in two different atomic transitions at 405.9 nm (Gd-152) and 413.4 nm (Gd-160) and directed collinearly through the laser ablation plume, separated on a diffraction grating, and detected with photodiodes to monitor transient absorption signals on a shot-by-shot basis. The method has been characterized first using Gd metal foil and then with particles of GdCl3 center dot xH(2)O as binary and ternary mixtures with Gd-152:Gd-160 isotope ratios ranging from 0.01 to 0.43. These particulate mixtures have been diluted with Columbia River sediment powder (SRM 435013) to simulate environmental samples and we show the method is capable of detecting a few highly-enriched particles in the presence of a > 100-fold excess of low-enrichment particles, even when the Gd-bearing particles are a minor component (0.08%) in the SRM powder and widely dispersed (1178 particles detected in 800,000 ablation laser shots). The implications for monitoring U-235:U-238 enrichment ratios in airborne particle samples, as related to the nuclear industry, are discussed. (C) 2009 Elsevier B.V. All rights reserved.