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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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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  

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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Abstract  

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.

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Abstract  

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-based k o-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.

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Abstract  

The single comparator method has been extended to a triple comparator method, using60Co,114m In and198Au. In this technique, thek-ratios of the elements to be analyzed, now determined against the three comparators, are corrected for each new ratio of thermal to epithermal reactor neutron flux. These flux ratios are calculated from the absolute activities of the three comparators. The thermal neutron activation cross-section and the resonance integral for the reaction113In(n,γ)114m In have been determined.

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Activation analysis of high-purity silicon

III. Multi-element activation analysis: Application of the triple comparator method

Journal of Radioanalytical and Nuclear Chemistry
Authors:
F. De Corte
,
A. Speecke
, and
J. Hoste

Abstract  

The triple comparator method is used for the analysis of impurities of high purity silicon by neutron activation. The ratios of the specific photopeak activities of the isotopes investigated to the specific photopeak activities of the gold, indium and cobalt comparators were determined. The triple comparator method avoids some tedious problems in the multi-element activation analysis and it is very well suited for the determination of ‘non-expected’ elements.

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Activation analysis of high-purity silicon

I. Determination of phosphorus

Journal of Radioanalytical and Nuclear Chemistry
Authors:
F. De Corte
,
A. Speecke
, and
J. Hoste

Abstract  

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.

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Abstract  

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.

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Abstract  

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 Φthe ratios in the 20<Φthe<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 (Φthe>100) channels. The Ioth-values for the mentioned Zr isotopes have been experimentally determined and compared with previously published data.

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