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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.

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Abstract  

ko-factors of 35 isotopes used in reactor neutron activation analysis were measured with a high degree of accuracy (1–2%). To minimize systematic errors, measurements were carried out using different reactor types, irradiation conditions (18 < Φse), Ge(Li) detectors, sample detector geometry, etc. Analyst-oriented tabulations including all necessary nuclear data, “best values”, as well as recommended ko-values are given to facilitate analytical work with the new method. Some practical aspects as well as limitations of the ko-method are also outlined together with the applied neutron flux and cross-section conventions.

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Abstract  

A description is given of the systematic errors which can be introduced when applying absolute or comparator standardization techniques to RNAA or ENAA at irradiation sites with a deviating 1/E1+α epithermal neutron flux distribution. A simple correction formula for a≠0 is presented and a survey is given of the present state-of-the-art for experimentala-monitoring and for the calculation or experimental determination of the effective resonance energy Ēr. Extensive error calculation leads to the conclusion that, with careful selection ofa monitors and of the nuclear data involved, the rather large errors (∼10% or more) are reduced, after correction fora, to uncertainties of about 2%.

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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.

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Abstract  

Some methods for the experimental α-determination in the 1/E1+α epithermal reactorneutron spetrum are critically compared with respect to their accuracy and precision. The analysis is based on the error propagation theory. Besides the general formulae numerical examples are elaborated for specific conditions in the Thetis reactor (Gent) and the WWR-M reactor (Budapest).

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Abstract  

The practical applicability of the 1/E1+α epithermal spectrum representation and of the effective resonance energy
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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
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-concept is not dependent on the choice of a reference energy. The usefulness of the parameters
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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).
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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.

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Abstract  

The induced activity of the99Mo isotope is mostly determined via the 140.5 keV γ-line, which is the strongest gamma-ray of its daughter,99mTc. Some recent literature, however, indicates a direct feeding of this energy level from the mother isotope as well. Considering the importance of this line in practice as well as the large controversy and scattering in relevant nuclear data available at present, a combined effort was made to remeasure this questionable absolute intensity. A relative method of irradiating a Mo-target with reactor neutrons and repeatedly measuring its (n,γ) induced activity relative to the 181.1 keV and 739.5 keV gamma lines of99Mo as internal references was used. The weighted average of different runs yielded γ(99Mo, 140.5 keV)=(5.07±0.37)%. As a consequence, when the 140.5 keV gamma line is used, the contribution from the99Mo mother isotope should always be taken into account, e.g. in neutron cross-section measurements and neutron activation analysis.

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Abstract  

A new method is developed for instantaneous α-determination in the 1/E1+α epithermal neutron spectrum. It is based on coirradiation of three bare resonance detectors, followed by gamma-counting on a calibrated Ge(Li)-detector. The technique is applied in two channels of the Thetis reactor (Gent) and the results are critically compared with those obtained by other methods.

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Abstract  

The present paper shows that the effective resonance energy
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introduced by RYVES, is a useful parameter for the correction of resonance integrals in non-ideal epithermal neutron spectra, which can be approximated by a 1/E1+α-flux distribution. The definition, the characteristics and the calculation of
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are discussed thoroughly. Tabulations are included, giving
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for 96 isotopes.
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