A novel method to obtain integral parameters of the orientation distribution function of textured polycrystals from wavelength-resolved neutron transmission spectra

VICENTE ALVAREZ, MIGUEL ANGEL; LALIENA, VICTOR; MALAMUD, FLORENCIA; CAMPO, JAVIER; SANTISTEBAN, JAVIER

Journal of Applied Crystallography

IUCr Journals

Año: 2021 vol. 54 p. 903 - 913

A novel method to estimate integral parameters of the orientation distributionfunction (ODF) in textured polycrystals from the wavelength-resolved neutrontransmission is presented. It is based on the expression of the total coherentelastic cross section as a function of the Fourier coefficients of the ODF. Thismethod is broken down in detail for obtaining Kearns factors in hexagonalcrystals, and other material properties that depend on the average of secondandfourth-rank tensors. The robustness of the method against three situationswas analyzed: effects of sample misalignment, of cutoff value lmax of the seriesexpansion and of experimental standard deviation. While sample misalignmentis shown not to be critical for the determination of Kearns factors and secondorder-rank properties, it can be critical for fourth-rank and higher-order tensorproperties. The effect of the cutoff value on the method robustness is correlatedto the standard deviation of the experimental data. In order to achieve a goodestimation of the Fourier coefficients, it is recommended that the experimentalstandard deviation be around 3?5% of the total scattering cross section of thematerial for the method to be stable. The method was applied for thedetermination of Kearns factors from transmission measurements performed atthe instrument ENGIN-X (ISIS) on a Zr?2.5 Nb pressure tube along two sampledirections and was shown to be able to estimate Kearns factors with an errorbelow 5%.