Monte Carlo simulation of neutron scattering by a textured polycrystal

LALIENA, VICTOR; VICENTE-ÁLVAREZ, MIGUEL ÁNGEL; CAMPO, JAVIER

Journal of Applied Crystallography

ELSEVIER SCIENCE BV

Año: 2019 vol. 53 p. 512 - 529

A method of simulating the neutron scattering by a textured polycrystal ispresented. It is based on an expansion of the scattering cross sections in terms ofthe spherical harmonics of the incident and scattering directions, which isderived from the generalized Fourier expansion of the polycrystal orientationdistribution function. The method has been implemented in a Monte Carlo codeas a component of the McStas software package, and it has been validated bycomputing some pole figures of a Zircaloy-4 plate and a Zr?2.5Nb pressure tube,and by simulating an ideal transmission experiment. The code can be used toestimate the background generated by components of neutron instruments suchas pressure cells, whose walls are made of alloys with significant crystallographictexture. As a first application, the effect of texture on the signal-to-noise ratiowas studied in a simple model of a diffraction experiment, in which a sample isplaced inside a pressure cell made of a zirconium alloy. With this setting, theresults of two simulations were compared: one in which the pressure-cell wallhas a uniform distribution of grain orientations, and another in which thepressure cell has the texture of a Zr?2.5Nb pressure tube. The results showedthat the effect of the texture of the pressure cell on the noise of a diffractogramis very important. Thus, the signal-to-noise ratio can be controlled byappropriate choice of the texture of the pressure-cell walls