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  • Author or Editor: K. Strijckmans x
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Abstract  

Standardization methods in activation analysis with charged particles are studied critically. Several approximate standardization methods that do not require knowledge of the excitation function are compared with the “numerical integration method” using excitation function data from the literature. It is shown that these methods yield accurate results if the threshold energy of the considered reaction is high and if sample and standard have a comparable Z value. A method that gives a rapid estimate of the maximum possible error is also presented. It is shown that for the “numerical integration method” the accuracy of the excitation function data has only a small influence on the overall accuracy. The influence of the accuracy of stopping power data and of possible deviations from Bragg's rule for light element standards is also considered.

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Abstract  

A method for the determination of sulphur in fly ash by instrumental proton activation analysis using the34S/p,n/34mCl reaction was developed. The 2128.5 keV and 3305.0 keV -rays of34mCl /t=32.0 min/ were measured on a Ge/Li/ -spectrometer, shielded with a lead absorber to attenuate low energy -rays. Irradiation and measuring conditions were optimized. The detection limit for instrumental analysis is 0.3 to 1 mg g–1 and the standard deviation is cca. 4% for a typical sample.

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Abstract  

A method for the determination of copper in zinc by proton activation analysis using the63Cu(p, n)63Zn reaction has been developed.63Zn has to be separated chemically from gallium and copper activities formed out of the zinc matrix and from indium activity formed out of cadnium impurity. Gallium radionuclides are retained on a cation exchanger in chloride medium and the residual activity is extracted in di-isopropyl ether. Copper and indium are subsequently extracted with cupferron in chloroform. The method was applied to BCR reference materials with a copper concentration at the g.g–1 level. The detection limit amounts to 0.5 g.g–1.

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Abstract  

This paper considers the variable isotopic composition of lead as a possible source of systematic errors in proton activation analysis. The importance of this source of error was evaluated for environmental and geological samples. As proton activation analysis is frequently used for the certification of lead, the error was determined for three sediment reference materials. Inductively coupled plasma-mass spectrometry was used for the determination of the isotopic composition of lead. The systematic error amounted for the sediments to approximately 1%.

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Abstract  

A procedure for the determination of nickel in copper by proton activation analysis has been developed. The57Ni activity induced was separated from the zinc and copper activity formed out of the copper matrix by anion exchange. Pure nickel was used as a standard. This method yields a reproducibility of 4% at the g·g–1 level. The detection limit is 0.03 g·g–1.

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Abstract  

In the14C-dating by accelerator mass spectrometry (AMS) iron and copper oxide are used during sample preparation. In an investigation on the origin of the14C-blank, which in practice determines the dating limit of AMS, the carbon contamination was measured in both reagents by deuteron activation analysis via the12C(d,n)13N reaction. A first batch of iron was analysed radiochemically and a carbon concentration of 37.6 g/g was found with a standard deviation of 2.7 g/g (3 analyses). In a second batch of iron concentrations between 66 and 150 g/g were found for 6 instrumental analyses, suggesting an inhomogeneous distribution of carbon. The carbon content in copper oxide was 17.8 (3.5) g/g for 3 instrumental analyses, but preference should be given to a radiochemical analysis. These figures indicate that the carbon impurities found in iron and copper oxide are possible causes of the14C-blank. However, a final conclusion can only be drawn if the14C concentration of the contaminating carbon and the amount of carbon released during sample preparation are known.

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Abstract  

Cadmium, thallium and lead are determined in environmental samples using the111,112,113Cd(p,xn)111In,203Tl(p,3n)201Pb and206,207,208Pb(p,xn)206Bi reactions.111In.201Pb and206Bi are chemically separated by anion exchange and anodic deposition of lead(IV). oxide. Detection limits are 6, 44 and 25 ng/g for cadmium, thallium and lead, respectively. The results obtained for certified reference materials are in good agreement with the certified values.

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Abstract  

Neutron self-shielding has been a factor of concern in the history of Instrumental Neutron Activation Analysis. When the sample to be analyzed cannot be made small enough in size and/or sufficiently diluted, this undesired phenomenon must be accounted for. Several analytical, semi-empirical and computational methods for estimating the thermal neutron self-shielding effects have been extensively discussed in the literature and this work aims at the experimental validation of some of these methods by neutron irradiation of cylindrical samples containing strong thermal neutron absorbers. The accuracy and the relative differences in the results between these methods are discussed for cylindrical samples with up to 40% thermal self-shielding, showing that a semi-empirical sigmoidal function can be more accurate in modeling this effect than other exact algorithms, where a maximum 2% relative difference to the experimental values was obtained.

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Abstract  

A novel method for the determination of lead in copper by proton, activation analysis has been developed. The bismuth activity formed was, separated from the matrix activity by anion exchange chromatography. Special attention was paid to possible systematic errors. The method was applied to BCR reference materials and yields a precision, of 2–3% at the g/g concentration level.

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Abstract  

Reactor channel characterization is commonly performed by irradiating bare and cadmium-covered “fluence rate monitors”, avoiding as much as possible the use of irradiation vials and spacers to position the monitors inside the channel. However, in routine k 0-Neutron Activation Analysis often samples are packed in small polyethylene vials prior to irradiation. This work aims at studying the impact of typical NAA polyethylene vials (~1 mm wall thickness) on the determination of the f and α channel-specific parameters through the “Bare”, “Cadmium-Covered” and “Cadmium-Ratio” methods. The impact of these vials on each method was studied for 3 irradiation channels of the Belgian Reactor 1 at SCK·CEN (Mol, Belgium) with low to high f and α-values. The net impact was 1% on each parameter. Inconsistencies between the different methods were found when the impact of the polyethylene was neglected, implying that all determination methods must be pooled and thin monitors should be used for an accurate channel characterization.

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