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  • Author or Editor: F. De Corte x
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Abstract  

After 36 years of operation, reactor Thetis at the Institute for Nuclear Sciences (Ghent University) was decommissioned in December 2003. On this occasion, a survey is presented of the characteristics and features of Thetis, which were opening the way to its significant contribution to NAA and its leading role in the development of the k 0-standardization. A summary is given, including a few specific examples, of fundamental analytical developments and practical applications based on irradiations in the reactor Thetis.

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Abstract  

Since its launching in the mid-70s, thek 0-standardization of NAA has been implemented and used in a growing number of laboratories worldwide. In the present paper, a survey is given of the situation in Europe, where the method or its associated subroutines are now operational in 22 industrial, governmental and university research centres spread over 12 countries plus IRMM of the European Union. In quite some of these places, not only practical applications are going on, but — as also reported here — further developments of the methodology are dealt with as well. These are related to such topics as the refinement of the fundamentals, the extension and improvement of the nuclear data library, the calibration of the Gedetector and of the neutron irradiation facility, the care for quality control/assurance and the upgrading of software for PC or mainframe.

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Abstract  

Values of 2200 m.s-1 cross sections, together with the associated nuclear data, are tabulated for 128 (n,g) reactions of interest in NAA. The values are derived from the Y2K database of experimentally measured k 0-factors.

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Abstract  

This review describes how the original `standardless' (absolute and single-comparator) NAA-calibration methods, introduced in the mid-1960s, were stepwise upgraded with respect to their accuracy and manageability, leading to the launching of the k 0-method in the mid 1970s. Next, an account is given of the achievements in the continuous development of the k 0-standardization of NAA up to the present. Topics highlighted are:the k 0 -data library, the development of dedicated calibration procedures, extensions and limitations, computerization and quality control/assurance. Finally, a short outline is given of the international dissemination of the k 0-methodology.

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Abstract  

A discussion is held on mutual influences and interactions between k 0- and (relative) comparator-type NAA. Examples are given concerning: (1) the application of comparator-type NAA in the quality control/quality assurance of the IRMM-530 Al-0.1%Au neutron flux monitor developed for use in k 0-NAA, (2) the utilization of the k 0-method of calibration as a tool for the quality assurance of comparator-type NAA, (3) the introduction of corrections for detection efficiency and true-coincidence (of primordial importance in k 0-NAA) in comparator-type NAA, (4) the development of k 0-type standardization for use in prompt gamma neutron activation analysis, and (5) the renewal of insights in the traceability of k 0- and comparator-type NAA.

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Abstract  

A discussion is held on some selected topics of importance in the standardization of reactor neutron activation analysis. The topics are related to the accuracy and the consistency of the nuclear data, the occurrence of flux gradients in the irradiation container, the extensions and modifications of the k0-method, and the determination of uranium via the counting of239Np and239U with a large Ge-detector or a LEPD.

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Summary  

The use of a Zr-Au-Lu alloy allows the simultaneous determination of all neutron spectrum parameters relevant to the k- 0standardization of NAA, in terms of both the Høgdahl and the Westcott convention. The present paper reports on the fundamental aspects (theoretical considerations, desired composition; gamma-spectrometry protocol) of this “all-in-one” alloy and on the experimental results (radiation stability; homogeneity tests) obtained for a variety of prototypes that were produced by some firms specialized in alloying technology. It is concluded that for the most recently produced material all criteria are fulfilled to pass on to the development of a certified Zr-Au-Lu alloy, which would be quite useful not only in the practice of k- 0NAA, but for neutron spectrum monitoring in general.

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Abstract  

Since 1996, two new cases were detected in our laboratory for which the elemental concentrations derived from k 0 neutron activation analysis seem questionable. These cases concern the inconsistencies observed (1) in the concentration of Ca obtained via 47Ca and 47Sc, and (2) in the concentration of Yb obtained via the 228.5 and 396.3 keV lines of 175Yb. A recommendation is made to re-evaluate the corresponding k 0-values or true-coincidence correction factors.

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Abstract  

The reloading of research reactor Thetis (INW, Gent), in April 1996, involved the re-calibration of the irradiation facilities used for k 0-NAA. In some channels, the values of the re-measured parameters f and a significantly deviated from the ones before reloading, and the effect of this on the concentration results is demonstrated. Some additional experimental work was done in two irradiation facilities, one well-thermalized and another with a hard neutron spectrum, in order to examine the behavior of a with neutron energies up to about 60 keV. This study was performed in the context of a lasting controversy regarding the accuracy of the k 0 and Q 0 values for the 95,97Zr-isotopes, especially in view of the high 94Zr(n,g) effective resonance energy. In the irradiation channels under consideration, no evidence was found of a versus energy dependence

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Abstract  

The performance of k 0-INAA was studied for the determination of the rare earth elements (plus Th and U) in the certification of four new BCR CRM's: 667 Estuarine Sediment, 690 Calcareous Soil, 670 Aquatic Plant and 668 Mussel Tissue. Our results are critically compared with the (later on) certified values, revealing slight discrepancies for the organic matrices aquatic plant and mussel tissue. Although these discrepancies were thought to be associated with the special procedure followed for moisture content determination, no convincing explanation could be found. Mention is also made of problems that are affecting the accuracy and precision of our results, especially with respect to multiplet deconvolution or otherwise troublesome peak fitting, spectral interferences, reaction interferences (notably from 235U-fission) and the non-1/v thermal cross section behavior. Eventually, detection limits for the REEs (+ Th and U) are calculated in the four materials, allowing to evaluate the applicability of INAA to these types of bio-environmental matrices.

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