A. Soares Leal

Bio: A. Soares Leal is an academic researcher from National Nuclear Energy Commission. The author has contributed to research in topics: Fission & Neutron activation analysis. The author has an hindex of 1, co-authored 1 publications receiving 3 citations.

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

Abstract: In the analysis of rare earth elements in samples containing uranium by k 0 -neutron activation analysis fission of 235 U was considered an undesired phenomenon until the “fission k 0 -factors” were introduced to account for natural-U fission interferences. In this work, by using a reverse perspective of the problem, the observed 235 U-fission and 238 U activation products (along with the k 0 -factors) were used to obtain information about the n ( 235 U)/ n ( 238 U) 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 ( 131 I and 140 La) were demonstrated to be reliable candidates for n ( 235 U)/ n ( 238 U) determination in environmental samples. The accuracy of this method was determined using several isotopic standards varying from a depleted to a highly enriched 235 U content. An overall 2.31±0.03% overestimation of the isotopic ratio was observed (within 95% confidence level).

Environmental Monitoring for Safeguards Using $k_{0}$ -standardized Neutron Activation Analysis

Abstract: 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 -standardised 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 U and n(235U)/n(238U) 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 k 0 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 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(235U)/n(238U) isotopic ratio analysis could also be performed.

Application of delayed neutron counting at CIAE

Abstract: Delayed neutron counting (DNC) was applied in quantitative determination of 235U/238U, quantitative determination of 235U and 239Pu in 235U–239Pu co-existing samples at China Institute of Atomic Energy (CIAE). In this work, natural uranium, enriched uranium and their mixtures were used in the determinations of 235U/238U ratios. The results indicated that delayed neuron counting combined with neutron activation analysis(NAA) and k0-NAA for the measurement of gamma rays emitted by 239U decay is suitable for fast determination 235U/238U ratio. In addition, the contents of 235U and 239Pu in 235U–239Pu co-existing samples can also be determined respectively.

Experimental k0 and k0-fission factors for the determination of the n(235U)/n(238U) enrichment levels and correction for 235U fission interferences in samples containing uranium

Abstract: In 2010 we investigated the applicability of the current k 0 and k 0-fission factors for the determination of the n(235U)/n(238U) isotopic ratio in multi-elemental samples containing uranium. An overestimation 3–4 % was observed in our determinations when employing the recommended 2003 k 0-literature. After a recalibration of all our laboratory instruments, a 3 % overestimation was still observed in this work when employing this nuclear data. Therefore we aimed at the experimental re-determination of these composite nuclear constants in order to enhance the reliability of the isotopic ratio determination method and the accuracy of our data-filtering algorithms. New k 0-fission factors are given for 7 nuclides that are not currently present in the 2012 k 0-database. Several additional k 0 factors are introduced for some nuclides in this library. Our k 0 results are also compared with those recently reported by Blaauw et al.