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  • Author or Editor: P. Bode x
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Abstract  

The Compton continuum in large sample neutron activation analysis has a measurable contribution from scattering of gamma-rays in the sample itself besides from scattering in the detector. The continuum, therefore, contains information on the sample’s composition, which may be made available by chemometrics. This hypothesis was tested on four types of animal fodder with similar amounts of mineral supplements. First results indicate indisputable discrimination of the sample types if using peakless parts of the gamma-ray spectra of the natural radioactivity of the materials as well as of those obtained after neutron activation of 1 kg samples. It indicates that the valuable information on differences in, e.g., organic constituents may be obtained by analyzing the Compton continuum.

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Abstract  

Metrology systems are being established by various countries for the worldwide comparability of data related to trade, industrial products, health, and the environment. This has in turn led to an increased interest in methods that have the highest possible accuracy and precision. The relevance of instrumental neutron activation analysis (INAA) for metrological science has been evaluated. It is concluded that INAA is a suitable technique for method validation, proficiency testing, development of reference materials and reference methods. Moreover, it is concluded that INAA may comply with the CCQM definition of a definitive or primary ratio method provided that the uncertainty in the results is reduced to much lower levels compared to those currently encountered in most NAA laboratories.

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Abstract  

Plastic products may contain high levels of trace elements, which, upon final incineration, may affect the environment. In the case of packing material, may affect food quality. In this work, instrumental neutron activation analysis was applied to the determination of As, Ba, Br, Cd, Co, Cr, Fe, Sb, Sc, Se, Ti and Zn in plastic materials originated from household and hospital wastes. Toxic elements such as Cd and Sb were found at the levels of mg·kg–1 in some food containers and also high levels of Ti were found in opaque packages. The accuracy and the precision of results were also evaluated by interlaboratory comparison.

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Abstract  

Commercially available pulse generators for use in -ray spectroscopy to correct for dead-time and pile-up losses share the problem that the fall-time of the output pulses does not match the fall-time of the detector pulse. Upon pulse shaping in the main amplifier the pulser's signals result in a considerable undershoot of the amplifier's output signal, which cannot be restored by theP/Z network. As a result, peaks in the -ray spectrum are broadened. Moreover, amplitude stability of the generators is often poorer than the overall gain stability of the spectrometer. To overcome these problems a special pulse generator has been developed at the Interfaculty Reactor Institute, which simulates Ge-detector signals. It generates pulses with a constant frequency of 25 Hz using a crystal oscillator controlled mercury relay. The stability of the generator's amplitude and frequency is extremely high and the peak-shapes in the -ray spectrum are not distorted.

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Abstract  

A benchmark study was carried out to verify whether MCNP is useful in the design stage of a PGNAA facility for large samples up to 1 m length and 0.15 m diameter, using a 2.54 cm diameter thermal neutron beam. For this facility neutron self-shielding and gamma-attenuation correction methods have to be developed. The relative spatial neutron-density distributions within three samples with different macroscopic scattering and absorption cross sections were studied in a comparison between an MCNP simulation and an irradiation experiment using copper wires as neutron monitors. The neutron density in the sample was within statistical agreement between experiment and simulation. Typically the relative spatial neutron-density distributions agreed to within 1%. Therefore, MCNP can be used in design studies for the development of a large sample PGNAA facility as specified.

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Abstract  

Implanted 74Ge and 120Sn concentrations in silicon (Si) layers were investigated by particle induced X-ray emission (PIXE), instrumental neutron activation analysis (INAA), Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS). Slight differences were observed in the results obtained. It was shown that PIXE and INAA are as powerful as the traditional RBS and SIMS spectroscopy for the investigation of thin layered Si.

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Abstract  

In this paper neutron resonance capture analysis (NRCA) is explored as a new method to analyse the elemental composition of materials and objects using a pulsed beam of epithermal neutrons and a time-of-flight system to recognize resonances of isotopes in the energy range from about 1 to 10 keV. Some test experiments have been carried out with bronze artefacts. Advantages, as compared to instrumental neutron activation analysis (INAA), are the low activation of the objects and the direct availability of results after the measurement.

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Abstract  

In a preliminary study performed with the waste rocks from the future uranium mine to be explored in Brazil, 106 samples were taken from the eight main lithologies found in the massif and analysed by instrumental neutron activation analysis (INAA) for 20 elements. For samples from the same lithology, a high variability in the concentration of most of the elements was found (coefficient of variation larger than 20%), which might be attributed to either insufficient homogenisation of minerals or to local variation within lithology. The hypothesis that the variability within the lithology does not have an influence to the total variability was tested by analysing 5 replicates of the 5 most contrasting samples from the predominant lithology (plagioclase-microcline-gneiss), chosen after applying statistical evaluation (principal components and cluster analyses). Results indicated that homogenisation of samples was adequate due to low variation among replicates. The hypothesis tested was rejected with a confidence level higher than 99% for all the elements, corroborating the large intra-lithology variability.

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Abstract  

Bone samples from iliac crest were obtained from apparently healthy female (n = 4) and male (n = 8) subjects with ages between 15–50. Cortical and trabecular parts were separated and soft tissues like fat, muscle and blood were removed. Calcium, Mg, Na, Cl, Fe, Zn, Br, Sr, and Cs were determined by instrumental neutron activation analysis and other techniques, and their relations were discussed. Fairly good agreement was obtained with literature data. These values may serve as reference values for subjects from a Turkish population.

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Summary  

This paper describes an analytical method using a nuclear-related technique for the detection of forbidden doping substances in the urine of race horses. The proposed method, adapted from the Méthode Alcaline Sur C-18 developed by the French Laboratoire de Contrôle Antidopage, is based on gas chromatography separation followed by mass spectrometry (GC-MS). The method was validated for caffeine, identified as the most frequent doping substance in the Brazilian horseracing activity. This validation is also a major requirement to achieve ISO/IEC 17025 laboratory accreditation. The validation has led to several metrological challenges because the decisions are largely based on qualitative results (“false-positive” and/or “false-negative”) and the degree of accuracy, as well as the traceability had to be determined in the absence of certified matrix reference materials.

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