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 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.
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.
Authors:F. de Corte, F. Bellemans, P. De Neve, and A. Simonits
Recently, the introduction was proposed of the Westcott-formalism in the ko-standardization method, in order to enable the handling of analytically important non-1/v (n, ) reactions. In the present paper some elucidations are given to the Westcott-basedko-method: the black box of Westcott's g+rs formalism is opened; procedures and formulas are given for the experimental determination of the flux parameters and a survey is presented of the status of the nuclear data.
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.
A method for the simultaneous determination of 21 elements in high purity silicon was developed by activation analysis. Extraction,
ion exchange, distillation and precipitation techniques were used combined with NaI(Tl) and Ge(Li) γ-spectrometry. Attention
was paid to the separation time, sensitivity and selectivity of the method.
32P was separated from the irradiated silicon matrix as ammonium phosphomolybdate and the activity was measured with a GM tube
or on a plastic scintillator. The second-order interference was taken into consideration.
Different methods for the determination of thermal-to-epithermal neutron flux ratio are reviewed and nuclear data for commonly
used monitor materials and for Zr isotopes are tabulated. It is shown that the use of the94Zr−96Zr isotope pair gives significant improvement in precision while measuring Φth/Φe ratios in the 20<Φth/Φe<200 range. When the single comparator method is applied, the use of the94Zr isotope is suggested as a comparator with the94Zr−96Zr isotope pair for simultaneous flux ratio determination. Theoretical calculations show that the Zr comparator-flux ratio
monitor gives better precision and accuracy than does Ru for two-thirds of the isotopes used for analysis in well thermalized
(Φth/Φe>100) channels. The Io/σth-values for the mentioned Zr isotopes have been experimentally determined and compared with previously published data.
Based on recently measured k0-factors and related nuclear data, an evaluation was performed, via the `activation method', of thermal (n,) activation cross sections. It concerns 15 analytically-relevant cases with a short half-life and/or with a complex activation-decay scheme: 20F, 41Ar, 60mCo/60Co, 71Zn, 77mSe, 80mBr/80Br, 104mRh/104Rh, 109mPd/109Pd/109mAg, 110Ag, 122mSb/122Sb, 124m2Sb/ 124m1Sb/124Sb, 134mCs/134Cs, 179mHf, 199mPt/199Pt/199Au and 205Hg.
In order to provide a tailored solution for the correction of the 235U interference in k0-NAA, fission k0-factors for the analytically relevant radionuclides/gamma-lines (versus gold as the comparator), are experimentally determined in four channels of the Gent THETIS reactor. A comparison is made with former data from the literature. The new evaluated results are to be implemented in the forthcoming upgrade of the DSMKayzero software package for k0-NAA.