Using pulsed neutron transmission for crystalline phase imaging and analysis

The total scattering cross section of polycrystalline materials in the thermal neutron region contains valuable information about the scattering processes that neutrons undergo as they pass through the sample. In particular, it displays characteristic discontinuities or Bragg edges of selected families of lattice planes. We have developed a pixelated time-of-flight transmission detector able to record these features and in this paper we examine the potential for quantitative phase analysis and crystalline phase imaging through the examination of a simple two-phase test object. Two strategies for evaluation of the absolute phase volumes (path lengths) are examined. The first approach is based on the evaluation of the Bragg edge amplitude using basic profile information. The second approach focuses on the information content of certain regions of the spectrum using a Rietveld-type fit after first identifying the phases via the characteristic edges. The phase distribution is determined and the coarse chemical species radiographic image reconstructed. The accuracy of this method is assessed

Background-filtered transmission diffraction with internal intensity calibration

It is inferred that by frequency filtering the logarithm of the time-of-flight spectrum of neutrons that have passed through a powdered isotropic crystalline sample a diffractogram may be obtained with many desirable properties for achieving high-quality refinement of structural parameters. Apart from multiple scattering no wavelength-dependent effects or corrections need to be introduced, which implies automatic internal calibration of the Bragg intensities. For utilization of the inherent high resolution of the transmission geometry, a Fourier chopper in the pulsed beam from an intensity-optimized quasi-steady-state moderator is suggested. Results of model calculations are presented.</jats:p