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Abstract  

A program of theoretical and experimental work was performed to develop a mathematical model which can represent all the parameters of the neutron activation analysis operation. However, we avoid absolute technique by using a sample containing the same element as the reference but having a different geometry and weight. In the present work we apply this model to determine the neutron, gamma-ray and neutron-and-gamma-ray self-shielding of the sample in relation with the number of counts in the total absorption peak. However the results obtained should be applied within the limitations of the method.

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Abstract  

The screening effect produced by a sample upon a standard located behind it is calculated. Curves for the secreening effect as a function of the sample material and of the sample depth are given.

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Abstract  

A method to compare calculated and experimental neutron attenuation coefficients when samples are of different geometries but the same material is proposed. The total removal cross-section for 14 MeV neutron activation analysis can be deduced from this comparison

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Abstract  

A semi-empirical method for photofraction determination is proposed: the photopeak efficiency is plotted as a function of the calculated total number of photons which interact at least once with the crystal for different sample to crystal distances. The tangent to this curve gives the photofraction at the point considered. No background subtraction or shielding is necessary.

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Abstract  

The neutron attenuation coefficient is determined in a double axis rotational system. The difference between a fixed system and a double axis rotational system is shown and curves for the neutron attenuation coefficient for the last case are drawn. The attenuated flux inside the sample is also drawn.

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Abstract  

Experimental verification of the formalism using nonidentical samples and standards in 14 MeV neutron activation analysis has been carried out. A standard was used containing the same element as the matrix; however its geometrical form is completely different. The formalism used yields satisfactory results even when the sample and the standard are counted at different distances from the detector.

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Abstract  

The errors of analysis due to the different parameters involved in 14 MeV neutron activation analysis method are studied. Formulae to calculate these erros have been developed when possible. Otherwise they have been evaluated for special experimental situations. Special cases where some parameters become critical, as far as precision is concerned, have been mentioned.

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Abstract  

A system has been designed and applied to study variations of the photofraction with distance. A137Cs and a54Mn gamma-source have been used; their distances to the detector were varied and the variations of the photofraction have been studied in the range of 1 to 300 mm.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
A. Elayi
,
P. Damiani
,
P. Collet
,
K. Gruel
,
F. Widemann
,
G. Grenier
, and
D. Parisot

Abstract  

Ancient silver-copper-tin alloyed Gaulish coins have been analyzed using 14 MeV neutron activation analysis. The method used takes into account all the differences in composition, geometry, position of irradiation and counting that may exist between the sample and the reference. The results of the analysis are accurate and permit interesting numismatic conclusions.

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