Full-pattern analysis of time-of-flight neutron transmission of mosaic crystals

F MALAMUD; J R SANTISTEBAN

JOURNAL OF APPLIED CRYSTALLOGRAPHY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016 vol. 49 p. 348 - 365

0021-8898

The energy-dispersive neutron transmission of mosaiccrystals contains a series of dips in intensity, at specific neutronwavelengths defined by the orientation of the specimen in the neutron beam. Wepresent a Rietveld-type full pattern analysis of neutron transmissionexperiments on mosaic crystals performed at spallation pulsed neutron sources. Theproposed analysis provides precise and simple determination of latticeparameters, mosaicity, extinction factors, and crystal orientation, and is especiallysuited to investigate the spatial variation of such microstructural informationacross macroscopic specimens with ~1 mm resolution. The effect of extinction on theintensity of Bragg reflections has been successfully accounted for by aparameter measuring the ratio between the beam attenuation due to Braggreflection to the combined attenuation due to absorption and scatteringprocesses. Experiments were performed at the ENGIN-X beamline,Isis Facility, UK, on several naturally occurring and man-made mosaic crystalsincluding a copper monochromator at temperatures between 55 K and 300 K, aniron-nickel meteorite and a natural pyrite crystal. Typical experimental resolutionsfound for lattice parameter and mosaicity are 0.03% and 7%, respectively. We discussthe possibilities of the technique for quantitative phase and/or textureanalysis of specimens composed by several grains or phases.