Advantages of combined IENAA and K0-factor technique in the determination of U and Th concentrations in exploration rock samples

The improved accuracy and precision of instrumental epithermal neutron activation analysis (IENAA), using the K0-factor technique over the conventional one-shot instrumental neutron activation analysis (INAA), in the measurement of uranium and thorium in geological samples is demonstrated. Using the geological reference material, GS-N, detection limits of 0.4 and 0.5 ppm were obtained for U and Th, respectively, by means of the INAA method, while superior 0.1 ppm and 0.25 ppm detection limits were obtained for these elements when the IENAA/K0-factor technique was employed. The concentrations of U in three samples of this reference material were measured as 8.05 ± 0.12, 8.12 ± 0.13 and 7.88 ± 0.19 ppm by the IENAA/K0-factor method showing an improved data disperson and accuracy over the values 6.17 ± 0.61, 6.39 ± 0.36 and 7.31 ± 0.39 ppm obtained by the INAA technique. These compare with the 8 ppm certified value for this element in this material. However, the improvement in precision and accuracy obtained for the thorium measurement is marginal. Analysis of a geological sample from Nigeria showed thorium to be more abundant than uranium in these rocks.