Since 1996, two new cases were detected in our laboratory for which the elemental concentrations derived from k0 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 k0-values or true-coincidence correction factors.
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
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.
The performance of k0-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.
Authors:F. de Corte, A. Simonits, A. de Wispelaere, and A. Elek
The determination of k0-factors has been continued covering now the relevant gamma-lines of 112 analytically interesting radionuclides. Experimental details are given, and an extended tabulation is presented of complex activation decay types and the associated expression for the parameters involved in the k0-method.
Authors:F. De Corte, A. Simonits, A. De Wispelaere, and J. Hoste
The present paper deals with the accuracy and applicability of the k0-standardization technique in NAA. Topics included are: user-oriented outline of the method, relevant nuclear data (k0, Q0, tc.), the non-1/E epithermal flux distribution, small detector separations and/or extended source geometries, (n, ) reactions with a Westcott-g1, primary interferences, subsequent (interrupted) irradiations, the non-constancy of the neutron flux during irradiation, and a final account of the accuracy. Although the paper is written in terms of the k0-methodology, a good deal of the considerations can be transferred to most types of single-comparator standardization.
Authors:A. Simonists, F. De Corte, A. De Wispelaere, and J. Hoste
In order to establish more accurate nuclear data for the zirconium isotopes94Zr and96Zr, joint experimental work has been conducted in three different reactor types. After carefully calibrating the neutron spectra in the irradiation channels used, nuclear constants k0 and Q0 were remeasured and found to be
The relevant effective resonance energies
. The epithermal neutron shielding factor Ge has been experimentally determined as a function of foil thickness. The results gave Ge(94Zr)=0.983 (±0.3%) and Ge(96Zr)=0.973 (±0.4%) for the most frequently used 0.125 mm foil thickness. Finally the half life of the97Zr isotope has also been remeasured to give T1/2(97Zr)=16.744±0.011 h with 1 limit.
Authors:F. De Corte, A. Simonits, and A. De Wispelaere
In the present paper, a tabulation is given of recommended Q0-values [the ratio of the resonance integral (I0) to the 2200 m·s–1 cross-section (
0)] for 107 (n, ) reactions of interest in NAA, including a revision and updating of formerly published results for 57 isotopes. The values were either critically evaluated from literature, or-in the majority of cases — experimentally determined according to the Cd-ratio method, with a correction for a non-ideal epithermal neutron flux distribution. These Q0-measurements were performed at INW, Gent, at KFKI, Budapest, and occasionally at Risø. A comparison is made with results obtained by other workers or with values derived from
0's and I0's quoted in recent compilations.
Authors:F. de Corte, K. Masumoto, A. De Wispelaere, and F. Bellemans
A dedicated NAA calibration method was developed for the determination of the neutron spectrum monitor elements Co, Au and Lu in alloyed wires and foils, with an accuracy of better than 1%. The method does not require quantitative micropipetting for preparing the standards, and leads to vanishing errors caused by flux inhomogeneities and by differences in counting geometry and gamma attenuation. Its performance was tested by analysing various NIST, IRMM and RX aluminium-based materials with certified or specified Co, Au or Lu content.
Authors:B. Smodiš, F. De Corte, and A. De Wispelaere
Although k0-factors and related nuclear data for 122 radionuclides of interest in (n,) reactor neutron activation analysis have been tabulated, there are still some reactions attracting interest with respect to the accuracy of the literature data. The present paper deals with the reaction130Ba(n,)131Ba, for which a more accurate half-life is proposed, together with re-evaluated Q0 and k0 factors. The new values are 11.53 days for T, 21.3 for Q0, and for the k0's 3.90×10–5, 2.75×10–5, 1.92×10–5 and 6.48×10–5 for the -rays at 123.8 keV, 216.1 keV, 373.2 keV and 496.3 keV, respectively.