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  • Author or Editor: J. Hostè x
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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  

The concept of the effective resonance energy
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, formerly introduced as a parameter in the absolute (e.g. k0-) standardization methodology of (n, ) activation analysis, is elucidated with respect to dimensioning, accuracy and usefulness.
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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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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).

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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  

USGS BCR-1 and G-2, NBS 1633a Coal Fly-Ash and a 7-element synthetic standard for biological material have been analysed in this work by reactor NAA, using the k0-standardization method. The analyses were performed independently in the analytical laboratories of the Institute for Nuclear Sciences (INW), Gent, and the Central Research Institute for Physics (KFKI), Budapest. This procedure allowed not only a comparison with the specified data or with other published values, but enabled a check of the consistency of our own results obtained in largely different experimental circumstances. As concluded the k0-standardization method combines general versatility (with respect to irradiation and counting conditions) with good accuracy, while keeping the experimental work as simple as possible. Since the k0 method is a computer-oriented technique, a FORTRAN IV program was designed and applied on a VAX 11/780 machine.

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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  

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.

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