Search Results

You are looking at 71 - 80 of 81 items for

  • Author or Editor: F. De Corte x
  • All content x
Clear All Modify Search

Abstract  

It was demonstrated that for the determination of the annual radiation dose for use in luminescence dating of sediments, one should be aware of possible material inhomogeneities when applying analysis methods (such as k 0-INAA) with sample intakes of the order of the gram (to be compared with Ge gamma-ray spectrometry in cylindrical or Marinelli geometry, the latter involving ∼1.5 kg material). Moreover, when trying to remove the inhomogeneity, care should be taken to avoid contamination of the elements investigated, especially in the case of low (K, Th, U)-content sand with a considerable abrasive action (such as the Ossendrecht coversand dealt with in the present work). Whereas contamination was indeed shown to happen when grinding the material in a porcelain mortar, a satisfactory technique proved to be agate-ball milling.

Restricted access

Abstract  

The applicability of the k0 standardization concept in ENAA has been investigated by comparing for 32 isotopes the experimentally determined ke, 0-values with those calculated from well-known k0 and Q0=l00 factors. It is concluded that the k-comparator method can be extended and applied in general to epicadmium (n, γ) activation analysis. Attention is also paid to some specific problems, such as the deviation from the ideal epithermal neutron flux distribution, the uncertainty in the effective Cd cut-off energy for the Cd-covers used, and the cadmium epithermal neutron transmission factor for which a literature survey is presented.

Restricted access

Abstract  

Some methods described in the literature for the determination of α in the 1/E1+α epithermal neutron spectrum are critically reviewed with respect to their accuracy. The multi resonance—detector method with Cd-covered irradiations, as used by SCHUMANN and ALBERT, is generalized by subtracting the epithermal 1/v-tail and by introducing the effective resonance energy, as defined by RYVES. The two-detector method of RYVES is modified by using Cd-ratio measurements, thus eliminating the introduction of systematic errors due to the inaccuracy of absolute nuclear data. The adapted methods are applied in channel 15 of the Thetis reactor (Gent).

Restricted access

Abstract  

A revision is made of some activation-decay types in k 0-NAA, aiming at the removal of (1) the inconvenience that a long-lived daughter radionuclide could in some instances only be measured after complete decay of a shorter-lived mother, and (2) the simplification that in some cases the measured gamma-ray emitted by the daughter radionuclide is not significantly contributed to by the mother. In view of this, new experimental and generalized k 0's and related data [Q 0, k 0(m)/k 0(g), etc.] for some analytically relevant activation-decay cases are presented for implementation in an updated version of the "Kayzero" software package. These cases are: 60mCo-60Co, 104mRh-104Rh, 109mPd-109Pd-109mAg, 122mSb-122Sb, 134mCs-134Cs, 199mPt-199Pt-199Au. For completeness, recent data for two additional cases are also included: 80mBr-80Br, 124m2Sb-124m1Sb.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: A. Simonits, F. De Corte, S. Van Lierde, S. Pommé, P. Robouch, and M. Eguskiza

Abstract  

The k 0 and Q 0 values for 94Zr(n,)95Zr(E = 724.2+756.7 keV) and 96Zr(n,)97Zr( ) 97mNb (E = 743.4 keV) were re-investigated. The aim was to further improve the reliability of the neutron spectrum characterization (f and monitoring) in k 0-NAA, based on "bare monitor" methods with the use of these Zr radionuclides. So as to achieve this goal, experimental determinations were performed in three reactor centers: KFKI AEKI, Budapest (WWR-M reactor); INW, Gent (THETIS reactor); SCK·CEN, Mol (BR1 reactor). The results were: Q 0(94Zr) = 5.306; Q 0(96Zr) = 251.6; k 0(95Zr, 724.2+756.7 keV) = 2.000E-4; k 0(97Zr/97mNb, 743.4 keV) = 1.237E-5. This means that the newly evaluated k 0-values are about 4.7% lower than the formerly reported ones. It is also emphasized that the 97Zr half-life is 16.74 hours, contrary to the 1% higher values usually reported.

Restricted access

Abstract  

A simple and accurate method is presented to evaluate the burnup effects involved in the neutron activation of 197Au prior to any neutron flux characterisation, based on the spectrometry of the 198Au and 199Au decay gammas. The obtained burnup factor can be used as input for reactor neutron field characterisation techniques using 197Au(n,)198Au as a monitor. This way an iterative procedure is avoided.

Restricted access

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.

Restricted access

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.

Restricted access

Abstract  

The computer program SOLANG, originally developed by MOENS et al. for the efficiency conversion via effective solid angles (

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\bar \Omega$$ \end{document}
(bulky source counted at the top of detector), discrepancies were below 7% in the whole range of gamma-energies considered (88–1115 keV), with an average of 3–4%. EXTSANGLE is extensive and flexible with respect to the data input, storage and output, thus contributing to the automation of a gamma-spectrometry laboratory dealing, for instance, with the k0-NAA and/or environmental radioactivity monitoring.

Restricted access

Summary  

Recently, in our laboratory an intercomparison was made of methods for the annual radiation dose determination (assessed from direct radiation counting and/or from the measurement of the K, Th and U contents) applied to luminescence dating of loess and sand sediment, whereby the emphasis was put on their precision and accuracy. Although these properties are important, the duration of the measurement is also a practically relevant aspect. Indeed, direct alpha, beta and gamma-counting can last a week or more, and the determination of K, Th and U via NAA can take up to three weeks to enable proper gamma-ray spectrometry of the long-lived 233 Th/233Pa. Therefore, in the present work the performance of k 0-based epiCd-NAA (ENAA, with irradiation under a cadmium cover) when applied to sediments is compared to k 0-NAA. As concluded, with the use of k 0-ENAA the analysis turnaround time could be considerably reduced from ~3 weeks to ~ 2.5days, while maintaining satisfactory accuracy, precision and determination sensitivity.

Restricted access