Authors:L. Sneyers, L. Verheyen, P. Vermaercke, and M. Bruggeman
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 k0-standardised Instrumental Neutron Activation Analysis (k0-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.
Authors:P. Vermaercke, F. Farina, L. Sneyers, M. Bruggeman, and J. Bouças
Several recent intercomparisons and certification exercises have shown that the determination of tin in e.g. food samples
and plastics is not straightforward. k0-Instrumental Neutron Activation Analysis (k0-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 k0-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.
Authors:F. Farina Arboccò, P. Vermaercke, L. Sneyers, and K. Strijckmans
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.
Authors:P. Vermaercke, P. Robouch, L. Sneyers, and F. De Corte
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 k0-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 k0-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.
Authors:F. Farina Arboccò, K. Strijckmans, P. Vermaercke, L. Verheyen, and L. Sneyers
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
k0-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.
Authors:P. Vermaercke, L. Sneyers, M. Bruggeman, A. De Wispelaere, and F. De Corte
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.