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Abstract  

Standardization methods in activation analysis with charged particles are studied critically. Several approximate standardization methods that do not require knowledge of the excitation function are compared with the “numerical integration method” using excitation function data from the literature. It is shown that these methods yield accurate results if the threshold energy of the considered reaction is high and if sample and standard have a comparable Z value. A method that gives a rapid estimate of the maximum possible error is also presented. It is shown that for the “numerical integration method” the accuracy of the excitation function data has only a small influence on the overall accuracy. The influence of the accuracy of stopping power data and of possible deviations from Bragg's rule for light element standards is also considered.

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Abstract  

The generalized temperature integral I(m, x) appears in non-isothermal kinetic analysis when the frequency factor depends on the temperature. A procedure based on Gaussian quadrature to obtain analytical approximations for the integral I(m, x) was proposed. The results showed good agreement between the obtained approximation values and those obtained by numerical integration. Unless other approximations found in literature, the methodology presented in this paper can be easily generalized in order to obtain approximations with the maximum of accurate.

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Abstract  

The235U fission neutron spectrum averaged cross section for the50Ti(n,)47Ca reaction was experimentally determined by irradiation of titanium with reactor neutrons. A value of (9.7±1.1) b was found for this cross section, using (307±11) b for the48Ti(n,p)48Sc spectrum-averaged cross section that was used as a standard. The50Ti(n,)47Ca spectrum-averaged cross section was also semiempirically evaluated by numerically integrating, through the ENDF/B-V representation of the235U fission neutron spectrum, the available experimental differential cross section data.

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Abstract  

A new method of calculation of parameters of enthalpy relaxation models is proposed. Regression analysis treatment compares the experimental and calculated values of relaxation enthalpy. The experimental values of relaxation enthalpy are obtained by numerical integration of the difference between the two DSC curves. Contrary to the overall shape of the DSC curve the integral values are not affected by particular heat flow conditions during the DSC experiment. The Narayanaswamy's numerical model based on the Kohlrausch—William—Watts relaxation function was used to calculate the theoretical values of relaxation enthalpy. The application of the proposed method on the DSC experimental data of enthalpy relaxation of As2Se3 is shown.

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Abstract  

A new approximate formula for temperature integral is proposed. The linear dependence of the new fomula on x has been established. Combining this linear dependence and integration-by-parts, new equation for the evaluation of kinetic parameters has been obtained from the above dependence. The validity of this equation has been tested with data from numerical calculating. And its deviation from the values calculated by Simpson's numerical integrating was discussed. Compared with several published approximate formulae, this new one is much superior to all other approximations and is the most suitable solution for the evaluation of kinetic parameters from TG experiments.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: E. L. Dorval, M. A. Arribére, S. Ribeiro Guevara, I. M. Cohen, A. J. Kestelman, R. A. Ohaco, M. S. Segovia, A. N. Yunes, and M. Arrondo

Summary  

We have measured the cross sections, averaged over a 235U fission neutron spectrum, for the two high threshold reactions: 75As(n,p)75mGe and 75As(n,2n)74As. The measured averaged cross sections are 0.292±0.022 mb, referred to the 3.95±0.20 mb standard for the 27Al(n,p)27Mg averaged cross section, and 0.371±0.032 mb referred to the 111±3 mb standard for the 58Ni(n,p)58m+gCo averaged cross section, respectively. The measured averaged cross sections were also evaluated semi-empirically by numerically integrating experimental differential cross section data extracted for both reactions from the current literature. The calculations were performed for four different representations of the thermal-neutron-induced 235U fission neutron spectrum. The calculated cross sections, though depending on analytical representation of the flux, agree with the measured values within the estimated uncertainties.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Hai-Qing Zhang, Bang-Fa Ni, Wei-Zhi Tian, Gui-Ying Zhang, Dong-Hui Huang, Cun-Xiong Liu, Cai-Jin Xiao, Peng Nie, and Hong-Chao Sun

Abstract  

An expression of γ-ray efficiency for large samples is proposed based on numerical integration of efficiencies over compositional point sources. The widely used expression on radial variation of HPGe efficiency for point source originally proposed by Noguchi et al. (Int J Appl Radiat Isot 32:17–22, 1980 [<cite>1</cite>]) was amended and a new expression was proposed. A comparison between the two expressions indicates that the newly proposed expression brings about an obvious improvement, and Self-absorption correction for a voluminous source is also given out by using the EID principle. The functional relationship between HPGe efficiency for γ-rays from a point source and the spatial position of the source was established. The results of this study can be applied in order to determine γ attenuation effects of unknown bulky samples with various shapes and materials.

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