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Abstract  

The thermal to epithermal neutron flux ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape (α) are essential parameters for the correct application of k 0-standardized neutron activation analysis. Several methods are applied for the determination of f and α. They are based on Cd-covered multi-monitor or on bare-irradiations methods. The recently developed and characterized synthetic multi-element standards (SMELS) were designed as a validation tool for the proper implementation of the k 0-NAA method in a laboratory. In particular, SMELS Type III contains Au and Zr, thus allowing the direct determination of f and α. It could, therefore, replace the traditional flux monitors. Furthermore, it could be used as a quality control material to monitor the stability of the irradiation facility and the detector. This paper presents the accuracy of the f and α determination and the feasibility of quality control using SMELS for irradiation channel Y4 of the BR1 reactor.

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Abstract  

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.

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Abstract  

Several recent intercomparisons and certification exercises have shown that the determination of tin in e.g. food samples and plastics is not straightforward. k 0-Instrumental Neutron Activation Analysis (k 0-INAA) offers some intrinsic quality control opportunities for the determination of the tin content in samples since several monitoring radioisotopes are formed. In this work we will discuss the validation of the determination of tin by k 0-INAA using different reference materials. The results show that only few of these radioisotopes are reliable in terms of accuracy and that from a survey of the tin content in a range of canned foods detection limits as low as 2 mg/kg can be achieved.

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Abstract  

A recent study on trace elements in beauty products and cosmetics sold on the Asian market has shown the presence of high levels of U, Th and rare earth elements in so called “Hormesis cosmetics.” For the purpose of comparison, some more information about trace elements in European cosmetics would be useful. In this paper the results obtained using k 0-standardised Instrumental Neutron Activation Analysis (k 0-INAA) for more than 20 trace elements in 20 different beauty products collected from the European market are presented. We found traces of Ba, As and Sb which is in breach with European legislation. For some of the other elements like Cr and Co further speciation is needed in order to evaluate their presence in beauty products.

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Abstract  

Reactor channel characterization is commonly performed by irradiating bare and cadmium-covered “fluence rate monitors”, avoiding as much as possible the use of irradiation vials and spacers to position the monitors inside the channel. However, in routine k 0-Neutron Activation Analysis often samples are packed in small polyethylene vials prior to irradiation. This work aims at studying the impact of typical NAA polyethylene vials (~1 mm wall thickness) on the determination of the f and α channel-specific parameters through the “Bare”, “Cadmium-Covered” and “Cadmium-Ratio” methods. The impact of these vials on each method was studied for 3 irradiation channels of the Belgian Reactor 1 at SCK·CEN (Mol, Belgium) with low to high f and α-values. The net impact was 1% on each parameter. Inconsistencies between the different methods were found when the impact of the polyethylene was neglected, implying that all determination methods must be pooled and thin monitors should be used for an accurate channel characterization.

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Abstract  

Several methods are in use for the determination of the thermal to epithermal neutron fluence rate ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape parameter (α). In our former work, it was proven that the recently developed and characterized Synthetic Multi-ELement Standard (SMELS) can be used for the fast verification of the stability of the irradiation parameters using the Au-Zr bare monitor method. However, this latter method using SMELS had a too low precision for an accurate determination of f and α. Therefore, the Cd-ratio for multi-monitor method using SMELS was investigated for two irradiation channels. As shown the material can also be used as a monitor for the calibration of an irradiation facility.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Em. Cincu, I. Manea, V. Manu, D. Barbos, O. Sima, I. Gustavsson, P. Vermaercke, N. Vajda, Zs. Molnar, and H. Polkowska-Motrenko

Abstract  

Samples of high alloy Stainless Steel SS 1 were analyzed by instrumental neutron activation analysis (INAA) at 5 research institutes in 4 European countries within the frame of an Inter-Laboratory Comparison (ILC) exercise aiming at checking if the results were independent of the standardization methods, and if INAA was accurate enough to contribute to certification. The mean element concentration values yielded by INAA were also compared with mean values obtained by atomic emission spectroscopy techniques at other laboratories that took part in the International Proficiency Testing organized by KIMAB Institute of Sweden, producer of the SS 1. The performances of the nuclear and atomic techniques were compared in terms of the z-score values calculated for 11 element concentrations evaluated by the two analytical ways. Finally, consideration is given to the ways in which highest accuracy and precision can be ensured for certifying stainless steels as CRMs.

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