Since its launching in the mid-70s, thek0-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.
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.
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 k0-factors.
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 k0-standardization. A summary is given, including a few specific examples, of fundamental analytical developments and practical
applications based on irradiations in the reactor Thetis.
A discussion is held on mutual influences and interactions between k0- 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 k0-NAA, (2) the utilization of the k0-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 k0-NAA) in comparator-type NAA, (4) the development of k0-type standardization for use in prompt gamma neutron activation analysis, and (5) the renewal of insights in the traceability of k0- and comparator-type NAA.
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 k0-method in the mid 1970s. Next, an account is given of the achievements in the continuous development of the k0-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 k0-methodology.
An electronic data base (DB) containing recently evaluated k0 and related data has been developed. The tables composing the DB are relationally linked to support data integrity. The purpose of the DB development is to make an official source of data used for electronic synchronization of the input parameters needed for the k0 methodology, which is developing in numerous laboratories. Such solution saves time when updating, ensures the quality of the primary data and hence of the analysis results, and due to the recording of the updating history preserves traceability of the data in time.
In order to calculate coincidence correction factors when measuring with a low-energy photon detector (LEPD), algorithms were developed for the description of the summing-out probabilities taking into account -LX in addition to - and -KX true-coincidences, where KX and LX can originate from internal conversion and electron capture. The accuracy of the calculation procedure is experimentally checked. The work presented here is part of an extension of the NAA k0-standardization to counting in a LEPD.
k0-Factors and related nuclear data are tabulated for 112 radionuclides of interest in (n, ) reactor neutron activation analysis. Whenever relevant, critical comments are made with respect to the accuracy of literature data for e. g. isotopic abundances, half-lives, absolute gamma-intensities and 2200 m · s–1 (n, ) cross-sections. As to the latter, a comparison is made with the values calculated from the experimentally determined k0-factors, by introduction of selected literature data for the input parameters.
The reloading of research reactor Thetis (INW, Gent), in April 1996, involved the re-calibration of the irradiation facilities used for k0-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 k0 and Q0 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