Frans De Corte

Recommended nuclear data for use in the k0 standardization of neutron activation analysis

Abstract k0 factors (composite nuclear constants) for use in the k0 standardization of reactor neutron activation analysis were experimentally measured with great care in several laboratories. The recommended values thus obtained for the relevant gamma rays of 144 analytically interesting radionuclides are tabulated, together with evaluated values for their associated parameters such as resonance integral to thermal cross-section ratios and effective resonance energies. A classification is also given of the various activation-decay types, to which the data are strictly correlated.

Advances in Fission-Track Geochronology

Advisory editorial board P. A. M. Andriessen G. Bigazzi A. Chambaudet A. J. W. Hurford G. A. Wagner Vrije Universiteit Amsterdam, The Netherlands Istituto di Geocronologia e Geochimica Isotopica, Pisa, Italy Universite de Franche-Comte Besancon, France University College London, United Kingdom Forschungsstelle Archdometrie der Heidelberger Akaddmie der Wissenschqften am Max-Planck-Institut fiir Kernphysik, Heidelberg, Germany

The Late Pleistocene loess deposits and palaeosols of eastern Belgium: new TL age determinations

Fourteen samples from the Pleistocene loess exposures at Kesselt (Belgian Limbourg) have been dated with the thermoluminescence method. Using the regeneration technique and a double analysis with two types of blue transmittant filters, reproducible age estimates were obtained up to about 130–140 ka. For the basal part of the late Weichselian (Brabant) loess and the underlying cryorurbated Nagelbeek Horizon we arrived at ages of 20–22 ka, which is consistent with the radiocarbon age of this horizon (22.3 ka). Our TL dates further constrain the formation of a lower luvisol profile, the Bt horizon of which has been correlated with the Rocourt palaeosol, to the period 50–60 ka. These dates, however, may overstimate the true age of the sediment because they were obtained on reworked loess. They indicate that this palaeosol was formed during a Middle Weichselian interstadial and not during the Eemian as is generally accepted. The boundary between the Weichselian and the older loess is situated at a lower level in the Kesselt profile. The loess bracketing the deeper tundra gleysols yielded TL ages up to 130–140 ka and the ages further rapidly increased with depth, indicating that the sediments may even be much older than Saalian.

The age and palaeoenvironmental significance of the Kalahari Sands in western Zimbabwe: a thermoluminescence reconnaissance study.

Thermoluminescence (TL) dating, has been applied to 10 samples from the aeolian Kalahari Sands of western Zimbabwe using the total bleach (additive dose) and regeneration techniques on coarse-grain quartz separates. The results suggest that the main phases of sand accumulation occurred between 10 and 96 ka. This Upper Pleistocene age is consistent with current opinions and argues against an important period of Holocene aeolian activity. The oldest sands were found in the Victoria Falls area where they overlie a ferricrete horizon. Based on our age determinations, we were able to constrain the age of this horizon to between 96±8 and 160±23 ka, which approximately coincides with the Last Integlaciation in the high latitudes. The youngest ages were obtained for sands from the southeastern part of the Hwange dune field but our limited sampling permits assigning only a minimum age of ca 20 ka to the ferricrete horizon observed in this area. Thus, we cannot ascertain if this ferricrete horizon is isochronous with the one at Victoria Falls or if it developed during a younger humid phase. Dune building activity most probably occurred in recurrent cycles of aridity interspersed with periods during which aeolian activity was limited or non-existent. Unfortunately, besides the ferricrete horizons, no other stratigraphical evidence of climatic fluctuation has been observed in the study area. However, it is possible that palaeosols have been entirely eroded before the subsequent deposition of new sediment, resulting in an incomplete stratigraphical record. The possibilities and limitations of luminescence dating for elucidating phases of climatic fluctuation in such situations are discussed briefly. In addition, we noticed serious discrepancies between the results yielded by the different techniques that were used for determining the dose rate. Hence, further work is needed to validate the accuracy of our dose rate measurements that may cause our TL ages to be about 30% too young.

Installation and calibration of Kayzero-assisted NAA in three Central European countries via a Copernicus project.

An account is given of the installation and calibration of k0-based NAA--assisted by the DSM Kayzero/Solcoi software package--at the KFKI-AEKI, Budapest, the NPI, Rez and the IJS, Ljubljana. Not only the calibration of the Ge-detectors and the irradiation facilities are discussed, but also other important topics such as gamma-spectrometric hard- and software, QC/QA of the IRMM-530 Al-Au flux monitor and the upgrade of the Kayzero/Solcoi code. The work was performed in the framework of a European Copernicus JRP, coordinated by the Laboratory of Analytical Chemistry, Gent, with DSM Research, Geleen, as the industrial partner.

Convergences And Divergences Of 2200 ms-1 (η,γ) Cross Section Data Selected From 1981-2001 Editions Of General And k0-NAA Evaluated Data Libraries

To assess the quality of the 2200 ms-1 (η,γ) cross section data relevant to neutron activation analysis (NAA), values selected from general and k0-NAA data libraries, over the past 20 years, are compared. For 24 interesting reactions, a remarkable convergence or divergence of the data was spotted. A main conclusion is that there is a need for traceability of σ0-data in compilations, which should include links to γ-ray intensity and isotopic abundance data.To assess the quality of the 2200 ms-1 (η,γ) cross section data relevant to neutron activation analysis (NAA), values selected from general and k0-NAA data libraries, over the past 20 years, are compared. For 24 interesting reactions, a remarkable convergence or divergence of the data was spotted. A main conclusion is that there is a need for traceability of σ0-data in compilations, which should include links to γ-ray intensity and isotopic abundance data.

A re-evaluation of k0 and related nuclear data for the 555.8 keV gamma-line emitted by the 104mRh-104Rh mother-daughter pair for use in NAA

Abstract A re-evaluation is made of the k0-factor and related nuclear data for the 555.8 keV gamma-ray of the 104mRh-104Rh mother–daughter pair that are important in neutron activation analysis (NAA). This study considers that the relevant level is also fed by the 4.34 min 104mRh mother (with an absolute gamma-ray emission probability γ2=0.13%) and not only, as assumed in former work, by the 42.3 s 104Rh daughter isotope (with γ3=2.0%). In view of this, generalised equations were developed for both the experimental determination and the analytical use of the k0-factor and of the associated parameters k0(m)/k0(g), Q0(m) and Q0(g) [(m):104mRh; (g): 104Rh], requiring the introduction of the γ2 and γ3 data and also of the 104mRh→104Rh fractional decay factor F2(=0.9987). The experimental determinations were based on irradiations performed in the BR1 reactor in Mol and the WWR-M reactor in Budapest. Furthermore, considering the special formation of the 555.8 keV gamma-ray, the procedure for true-coincidence correction was revised as well. All this led to the compilation and recommendation of a new set of ‘k0-NAA’ data.

Methods for quality control/quality assurance of k0-assisted neutron activation analysis

A survey is given of methods that were developed and applied for controlling and assuring the quality of k0-assisted neutron activation analysis. These methods are: 1. Parallel but independent determination, in several laboratories, of the fundamental nuclear data, leading to the detection and elimination of systematic uncertainties; 2. Identification and quantification of all sources of uncertainty related to every step and parameter involved, and the application of error propagation theory to make an uncertainty budget of the analytical result; 3. Overall accuracy control via the analysis of various reference materials; 4. Detailed study of the traceability, and its enhancement by the introduction of neutron flux monitor alloys with certified composition; and 5. Currently, the development of synthetic multi-element standards (“SMELS”) for testing the performance of the k0-standardization when implemented in a laboratory.A survey is given of methods that were developed and applied for controlling and assuring the quality of k0-assisted neutron activation analysis. These methods are: 1. Parallel but independent determination, in several laboratories, of the fundamental nuclear data, leading to the detection and elimination of systematic uncertainties; 2. Identification and quantification of all sources of uncertainty related to every step and parameter involved, and the application of error propagation theory to make an uncertainty budget of the analytical result; 3. Overall accuracy control via the analysis of various reference materials; 4. Detailed study of the traceability, and its enhancement by the introduction of neutron flux monitor alloys with certified composition; and 5. Currently, the development of synthetic multi-element standards (“SMELS”) for testing the performance of the k0-standardization when implemented in a laboratory.

Method for the determination of neutron field monitor burnup effects by gamma-spectrometry.

A methodological concept is developed to determine the burnup of certain neutron flux monitors in an unknown, intense reactor neutron field. In particular, it is shown how to evaluate the burnup effects involved in the neutron activation of 197 Au prior to any neutron flux characterisation, based merely on the spectrometry of the 198 Au and 199 Au decay gamma rays. Such independent detection method of the burnup factor allows a principally correct evaluation of the specific count rate of the irradiated monitor, which serves as a basic input for the determination of neutron field parameters.

The k 0 -standardization method and its multifacetness: an eminent tool to master NAA

It is outlined in the present paper that the continuous development and multi-purpose implementation of the k0-standardization in NAA implies the awareness, study and understanding of its many inherently associated facets. Considering this aspect, it is concluded that the k0-method can be regarded as an eminent tool to master neutron activation analysis in general.