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- Author or Editor: A. De Wispelaere x
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Abstract
Loess sediment was prepared and characterized with well-established K, Th and U contents, and corresponding 40K, 232Th and 235,238U activities, intended for use as a reference material in the annual radiation dose determination for luminescence dating. To this purpose, loess was collected in Volkegem, Belgium, and — after drying, pulverizing and homogenizing — characterized via k 0-INAA and HPGe gamma-ray spectrometry. This led to 12 kg material with a grain size below 50 μm, with established K, Th and U homogeneity, with the 232Th and 238U decay series proven to be in equilibrium, and with the following K, Th and U reference data: K = 16.5±1.5 g·kg−1 (40K = 497±45 Bq·kg−1); Th = 10.4±0.6 mg·kg−1 (232Th = 42.2±2.5 Bq·kg−1); U = 2.79±0.12 mg·kg−1 (238U = 34.5±1.5 Bq·kg−1; 235U = 1.59±0.09 Bq·kg−1; 235+238U = 36.1±1.7 Bq·kg−1). These data were confirmed via comparison with the results from NaI(Tl) field gamma-ray spectrometry, thick-source ZnS alpha-counting and thick-source GM beta-counting (after converting all data to Gy·ka−1). The reference material is available (as aliquots up to 200 g) from the Ghent Luminescence Laboratory to all interested luminescence dating laboratories upon motivated request.
Abstract
One of the basic steps in luminescence dating is the determination of the annual radiation dose. Among the suitable determination methods in the case of sediment dating is HPGe gamma-ray spectrometry, primarily yielding the concentrations of K, Th and U via measurement of gamma-rays emitted by 40K and by 232Th and 235,238U and their decay products. These determinations involve both large-volume samples (with cylindrical or Marinelli geometry) and low-energy gamma-rays (down to the 210Pb 46.5 keV line). In view of this, calculations have been made in the present work in order to investigate possible inaccuracies related to gamma-ray attenuation, which may be different in samples and calibrants which have considerably different composition (elemental concentration and packing density). The calculations are based on the introduction of correction factors containing “effective solid angles” (proportional to the peak detection efficiencies), which are believed to give “correct” concentration results. It was found that, in some cases, significant errors could be committed when not performing proper corrections. Therefore, it is concluded that in practice this possible source of inaccuracy should be kept in mind, thus making it necessary to have a fair knowledge of the properties of the materials (samples and calibrants) under investigation.
Abstract
Several methods are in use for the determination of the thermal to epithermal neutron fluence rate ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape parameter (α). In our former work, it was proven that the recently developed and characterized Synthetic Multi-ELement Standard (SMELS) can be used for the fast verification of the stability of the irradiation parameters using the Au-Zr bare monitor method. However, this latter method using SMELS had a too low precision for an accurate determination of f and α. Therefore, the Cd-ratio for multi-monitor method using SMELS was investigated for two irradiation channels. As shown the material can also be used as a monitor for the calibration of an irradiation facility.
Abstract
A new method is presented to calculate with improved accuracy the absolute peak efficiency of cylindrical Ge and Ge(Li) detectors for point, disk and cylinder sources, positioned at any source-detector distance. Moreover attention was paid to true-coincidence effects. The method is extensively tested and applied for the analysis of reference materials. The accuracy turned out to be 3% or better.
Abstract
At the 
Special Sessionk
0
of the MTAA-8 (Vienna, 1991), and later on at the Intemationalk
0 Users Workshop-Gent (1992), progress was reported with respect to the development and use of computer codes in order to mould thek
0-standardization of neutron activation analysis into an effective working instrument. Among others, this resulted in the software package KAYZERO for PC DOS, which was designed and distributed by DSM Research (Geleen, NL), and which is based on thek
0-methodology, algorithms and nuclear data file developed and created at the INW (Gent, B) and the KFKI (Budapest, H), the traditional
k
0-centres. One of the most recent initiatives is a project in the framework of the COPERNICUS programme of the Commission of the European Union. It uses the synergism of a Joint Research Project to give an impulse to the exploitation of KAYZERO-assisted NAA as a manageable and competitive analytical tool in industry and environmental sanitation in Hungary, the Czech Republic and Slovenia. An outline is given of the strategy worked out in this JRP, emphasizing the procedures applied in the three institutes for the calibration of their irradiation facilities and Ge-detectors, quality control and assurance procedures following the implementation of the method, and the identification and tackling of the practical analytical problems which are of relevance to the Central European partner countries.
Abstract
A study is made of the corrections that are needed in the evaluation of the annual radiation dose, for use in TL/OSL-dating, via NaI(Tl) field gamma-ray spectrometry (monitoring of K, Th and U), calibrated via voluminous blocks that are simulating the Auger hole measuring conditions. Two cases are considered: the 
Heidelberg
granite calibration block, which was found to be quasi-infinite, and the Oxford concrete calibration blocks, for which effective concentrations of elements are reported so as to account for their non-infiniteness. The calculations, via the software package ANGLE, are based on the concept of effective solid angles for Marinelli geometries.
Abstract
This paper reports on the contribution made by some cooperating laboratories to the further development of the k0-method. As to the extensions and improvements, emphasis is put on the availability of an Al–0.1% Au reference material for the k0-standardization of NAA, on the counting of large-diameter samples, on the use of a low-energy photon detector, and on the introduction of the Westcott formalism for the handling of 
non-1/v
(n, 
) reactions. A survey is given of a large variety of scientific and industrial applications, including the analysis of biological, geological and geochronological samples, various kinds of reference materials, high-purity products and ceramics, and a number of environmental pollution indicators. As shown, the advantage of the k0-standardization will be fully exploited with an increasing level of automation in NAA laboratories. Eventually, new measurements and evaluations of k0-factors and related nuclear data are given in an Appendix.
Abstract
True-coincidence summing correction is an essential element in k 0-based NAA1 and becomes important when samples are counted with a high efficiency detector. This may be the case where large detectors are used or where samples are counted in or in the vicinity of the detector in order to achieve low detection limits in conjunction with low-flux reactors. In some laboratories coincidence correction is accomplished by calculating the coincidence correction factors. Since experimental validation of the calculations will reveal only the most significant errors and is a laborious task due to the high number of radionuclides involved, three laboratories decided to compare their calculated coincidence factors. Each laboratory uses a different software package. A comparative performance analysis was made of COINCALC developed at the INW of the University of Gent (implemented in SOLCOI by DSM Research), the software of the IRI, University of Delft, the Netherlands, and the software of the Ecole Polytechnique, Montreal, Canada. The overall approach, data and algorithms were chosen independently by each institute as the software was being developed and, so, the comparison has yielded a number of interesting conclusions. A follow-up investigation of the discrepancies found will probably allow the performance of each program to be improved.
