The use of k0-NAA for the determination of the n(235U)/n(238U) isotopic ratio in samples containing uranium

In the analysis of rare earth elements in samples containing uranium by k0-neutron activation analysis fission of 235U was considered an undesired phenomenon until the “fission k0-factors” were introduced to account for natural-U fission interferences. In this work, by using a reverse perspective of the problem, the observed 235U-fission and 238U activation products (along with the k0-factors) were used to obtain information about the n(235U)/n(238U)1 isotopic ratio in the samples. The relevant formulae and data-filtering algorithm were implemented in a home-made computer software, allowing automated evaluation and selection of unbiased data. Two radioisotopes (131I and 140La) were demonstrated to be reliable candidates for n(235U)/n(238U) determination in environmental samples.The accuracy of this method was determined using several isotopic standards varying from a depleted to a highly enriched 235U content. An overall 2.31±0.03% overestimation of the isotopic ratio was observed (within 95% confidence level).