Search Results

You are looking at 41 - 50 of 81 items for

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

Abstract  

The effective resonance energy

\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} $$\left( {\bar E_r } \right)$$ \end{document}
, a useful parameter when correcting the resonance integral for a non-ideal epithermal neutron flux distribution, can be experimentally determined by coirradiating the investigated isotope with a comparator isotope whose effective resonance energy is accurately known. The principle of the method is outlined and the error propagation functions are studies in detail. The usefulness of the
\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} $$\bar E_r$$ \end{document}
-comparator technique is tested for a few isotopes.

Restricted access

Abstract  

The thermal to epithermal neutron flux ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape (α) are essential parameters for the correct application of k 0-standardized neutron activation analysis. Several methods are applied for the determination of f and α. They are based on Cd-covered multi-monitor or on bare-irradiations methods. The recently developed and characterized synthetic multi-element standards (SMELS) were designed as a validation tool for the proper implementation of the k 0-NAA method in a laboratory. In particular, SMELS Type III contains Au and Zr, thus allowing the direct determination of f and α. It could, therefore, replace the traditional flux monitors. Furthermore, it could be used as a quality control material to monitor the stability of the irradiation facility and the detector. This paper presents the accuracy of the f and α determination and the feasibility of quality control using SMELS for irradiation channel Y4 of the BR1 reactor.

Restricted access

Abstract  

After critical evaluation of a number of existing standardization methods a new approach introducing generalized k0-factors was suggested in 1975 for use in (n, γ) reactor neutron activation analysis (RNAA). In order that the new method could soon be applied competitively in actual analytical work a cooperation between the Activation Analytical Laboratories of the Central Research Institute for Physics (KFKI), Budapest and the Institute for Nuclear Sciences (INW), Gent was established to determine the k0 and other related nuclear data (Q0, T1/2, Ēr, etc.) with a high accuracy, to develop procedures for monitoring essential irradiation and measuring parameters (Φse, α, ∈p,

\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}
, etc.) as well as to share experiences when applying the method. This paper summarizes the main results of this cooperative work obtained in the last five years. The current status and recent developments in the k0-method are reviewed and a “Status and Request List” compiled from more than a thousand surveyed nuclear data on about 150 analitically important (n, γ) reactions in being prepared to suggest new or refined measurements and to prevent the use of unreliable data.

Restricted access

Abstract  

By comparison of experimental k0-factors, determined in reactor positions with greatly different thermal-to-epithermal neutron flux ratios, and by comparison of experimentally determined and theoretically calculated k0-factors, it is possible in some cases to select best values from literature data for (n, γ) activation cross-sections and for absolute gamma intensities. This is demonstrated for97Zr,95Zr,56Mn and65Zn.

Restricted access

Abstract  

The practical applicability of the 1/E1+α epithermal spectrum representation and of the effective resonance energy

\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} $$\bar E_r$$ \end{document}
in NAA is investigated. Attention is paid to fundamental considerations such as definitions and approximations, error propagation functions, uncertainty statements, reliability of nuclear data and formal dimensioning problems. As to the latter, it is concluded that the applicability of the
\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} $$\bar E_r$$ \end{document}
-concept is not dependent on the choice of a reference energy. The usefulness of the parameters
\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} $$\bar E_r$$ \end{document}
in NAA is demonstrated by new experimental evidence obtained from and Q0 determinations in three different reactors: the WWR-M reactor (Budapest, Hungary), the THETIS reactor (Gent, Belgium) and the DR-3 reactor (Risø, Denmark).

Restricted access

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.

Restricted access

Abstract  

The116Sn (n, γ)117mSn reaction commonly used in reactor-neutron activation analysis (RNAA) turned out to be seriously interfered by the117Sn (n, n′)117mSn reaction, as observed from irradiation in channels with largely different neutron thermalization. To estimate the magnitude of this primary interference an attempt was made to determine the relevant fission neutron averaged cross-section, yielding approximately σn, n, (117Sn)==0.09±0.01 barn. This value—believed to be the first measured and published—is remarkably high especially when compared to the 2200 m·s−1 cross-section σo[116Sn(n, γ)117mSn]=0.006 barn.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: R. van Sluijs, D. Bossus, J. Konings, F. De Corte, A. De Wispelaere, and A. Simonits

Abstract  

To account for varying dead time (frequently occurring when the measuring time is comparable with the half lives of the radionuclides in question) the use of Westphal's Loss-Free Counting technique (LFC) is preferable. However, standard gamma-ray spectrum deconvolution programs can not be applied in connection with LFC spectrometers, since this technique strongly influences the counting statistics of measured spectra. As consequence, erroneous results are likely to arise when applying peak search routines or when calculating the standard deviation of fitted peak areas or detection limits. To overcome these shortcomings, an LFC module equipped with Dual LFC Mode option should be used: this accumulates an LFC-corrected spectrum simultaneously with an uncorrected spectrum. The KAYZERO evaluation software has been modified to handle such tandem spectra.

Restricted access

Abstract  

Recommended k0-factors and related nuclear data for use in (n, ) activation analysis are given for 72 isotopes. In addition the basic nuclear constants and experimental parameters needed in the k0 standardization method are reviewed. For convenient data reduction, computer programs were developed.

Restricted access

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.

Restricted access