Environmental monitoring for safeguards using k0-standardised neutron activation analysis

Multi-elemental analysis of samples containing uranium by Instrumental Neutron Activation Analysis (INAA) has been generally known as a problematic task due to the numerous radioisotopes produced from the uranium fission when the sample is irradiated with thermal neutrons. In k0-standardised NAA (k0-NAA) it is possible to correct for this effect through the introduction of k0-fission factors. In this work the aim was to determine the feasibility of k0-NAA as a screening technique for accurate U and n(235U)/n(238U) isotopic ratio determination (we further refer to the technique as k0-UNAA) and where k0-UNAA could be positioned versus the other screening techniques. In k0-UNAA we use an adapted k0 formalism to determine the n(235U)/n(238U)-ratio. Several swipe samples spiked with different isotopic ratio's U were analysed and demonstrate the feasibility of k0-UNAA as an accurate and reliable screening method for the quantification of environmental samples up to several tens of ng. At these levels the uranium concentration can be quantified with a reasonable uncertainty and reliable n(235U)/n(238U) isotopic ratio analysis could also be performed. (authors)