Measurement of uranium isotope ratios in solid samples using laser ablation and diode laser-excited atomic fluorescence spectrometry

A diode laser is used for the selective excitation of U-235,,and U-238 in,,laser-induced plasma applying Nd:YAG laser pulses to UO2 samples. The diode laser is rapidly scanned immediately following each laser sampling and the resonance atomic fluorescence spectrum for both isotopes is obtained on a pulse-to-pulse basis. Time-integrated measurements, with the diode laser fixed at either isotope, were also made. Optimum signal-to-noise was obtained at a distance of 0.8 cm from the sample surface, a pressure of 0,9 mbar and a Nd:YAG laser pulse energy of 0.5 mJ (880 MW cm(-2)). Three samples with 0.204, 0.407 and 0.714% 235U were measured. For example, for the UO2, pellet with the natural uranium isotopic composition (99.281% 238U,,and 0.714% U-235), th, accuracy and precision were 7% and 5% (460 shots), respectively, limited by the continuum emission background from the laser-induced plasma. (C) 1999 Elsevier Science B.V. All rights reserved.