K0-NAA for the Determination of Trace Elements in a Synthetic Material: a Collaborative Study

As part of an interlaboratory comparison in order to certify a synthetic material to be used for the validation of the proper implementation of k0-NAA a collaborative trial was organised. Based on this collaborative study, reproducibility relative standard deviations valued ranged typically from 2 to 5%. These values were compares with the Horwitz criterium leading to HORRAT values in most cases well below 1, although two exceeding 1, depending on the element to be determined. It could be concluded that k0-NAA is a very precise method, but that still some inconsistencies for certain elements remain.JRC.D.8-Food safety and qualit

Using k0-UNAA for the determination of depleted uranium in the moss biomonitoring technique

The use of ammunition containing depleted uranium (DU) in several military actions is of growing health concern to the population related to the risk arising from contamination of the environment with DU penetrators and dust. Environmental monitoring of uranium and its isotopic ratios therefore become important parameters since they allow for source identification. Neutron activation analysis according to the k0-standardisation not only allows for quantification of trace elements including uranium, but it can also provide information about the 235U/238U isotope ratio. The application of this method as a screening technique to moss samples, as a bio-indicator for this atmospheric pollution, was evaluated for samples spiked with different 235U/238U isotope ratios. Detection limits of about 0.6 ng/g and 6 ng/g were obtained for 235U and 238U, respectively. The concentration of natural uranium found in moss samples is however the limiting factor, reducing the quantification limit for DU to 400 ng/g

Experimental evaluation of epithermal neutron self-shielding for 96Zr and 98Mo

In a previous work we experimentally tested some neutron self-shielding calculations methods for thermal absorbers, from which the semi-empirical "sigmoid method" gave the most accurate results. In this work we aim at evaluating the accuracy of this method on the epithermal self-shielding phenomena as compared to the analytical "MatSSF method". Metallic foils of Zr and Mo were compactly stacked together into small cylinders (or disks) of different thickness, allowing for up to 20 % epithermal self-shielding when irradiated on two channels of the BR1 reactor. A 2 % relative difference between calculated and experimental self-shielding factors was obtained from the MatSSF method when a perpendicular source-sample axial configuration was assumed, while the isotropic or the co-axial configuration alternatives gave up to 10 % relative differences. On the other hand, the sigmoid method gave relative differences of up to 6 % that can be reduced to just 2 % by applying the "effective" epithermal absorption cross-sections for Mo-98 and Zr-96 proposed in this work

Experimental validation of some thermal neutron self-shielding calculation methods for cylindrical samples in INAA

Neutron self-shielding has been a factor of concern in the history of Instrumental Neutron Activation Analysis. When the sample to be analyzed cannot be made small enough in size and/or sufficiently diluted, this undesired phenomenon must be accounted for. Several analytical, semi-empirical and computational methods for estimating the thermal neutron self-shielding effects have been extensively discussed in the literature and this work aims at the experimental validation of some of these methods by neutron irradiation of cylindrical samples containing strong thermal neutron absorbers. The accuracy and the relative differences in the results between these methods are discussed for cylindrical samples with up to 40% thermal self-shielding, showing that a semi-empirical sigmoidal function can be more accurate in modeling this effect than other exact algorithms, where a maximum 2% relative difference to the experimental values was obtained

Measurement of the Isotopic Composition of Germanium by k0-INAA and INAA

In experiments searching for neutrinoless double beta-decay high-purity Germanium detectors enriched in 76Ge will be used. Due to the nature of these experiments the isotopic composition of the enriched germanium is an important parameter. In order to determine the 76Ge/74Ge isotopic ratio in this new material, but also in natural and depleted samples, the feasibility of using k0- and relative standardisation neutron activation analysis for the determination of isotopic ratios was investigated. The paper will discuss the accuracy and the estimated uncertainty of both methods in general. It was found that both techniques are useful for the determination of isotopic ratios. The analysis also demonstrated that the k0-data forGe should be re-evaluated.JRC.D.4-Nuclear physic

Environmental monitoring for safeguards using k(0)-standardized 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 k(0)-standardized NAA (k(0)-NAA), it is possible to correct for this effect through the introduction of k(0)-fission factors. In this work, the aim was to determine the feasibility of k(0)-NAA as a screening technique for accurate and isotopic ratio determination (we further refer to the technique as k(0)-UNAA) and where k(0)-UNAA could be positioned versus the other screening techniques. In k(0)-UNAA, we use an adapted formalism to determine the n(U-235)/n(U-238)-ratio. Several swipe samples spiked with different isotopic ratios were analyzed and demonstrate the feasibility of k(0)-UNAA as a 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(U-235)/n(U-238) isotopic ratio analysis could also be performed