Abstract
Current status of Bragg-edge/dip neutron transmission analysis/imaging methods is presented. The method can visualize real-space distributions of bulk crystallographic information in a crystalline material over a large area (~10 cm) with high spatial resolution (~100 μm). Furthermore, by using suitable spectrum analysis methods for wavelength-dependent neutron transmission data, quantitative visualization of the crystallographic information can be achieved. For example, crystallographic texture imaging, crystallite size imaging and crystalline phase imaging with texture/extinction corrections are carried out by the Rietveld-type (wide wavelength bandwidth) profile fitting analysis code, RITS (Rietveld Imaging of Transmission Spectra). By using the single Bragg-edge analysis mode of RITS, evaluations of crystal lattice plane spacing (d-spacing) relating to macro-strain and d-spacing distribution’s FWHM (full width at half maximum) relating to micro-strain can be achieved. Macro-strain tomography is performed by a new conceptual CT (computed tomography) image reconstruction algorithm, the tensor CT method. Crystalline grains and their orientations are visualized by a fast determination method of grain orientation for Bragg-dip neutron transmission spectrum. In this paper, these imaging examples with the spectrum analysis methods and the reliabilities evaluated by optical/electron microscope and X-ray/neutron diffraction, are presented. In addition, the status at compact accelerator driven pulsed neutron sources is also presented.
Highlights
Wavelength-resolved neutron transmission imaging experiments using the time-of-flight (TOF)method at pulsed cold/thermal neutron sources can position-dependently obtain Bragg-edge transmission spectra from a polycrystalline material, or Bragg-dip transmission spectra from a coarse-grained/single-crystal material, at each pixel position of a neutron TOF-imaging detector.Bragg-edge is the profile caused by diffraction phenomenon of neutrons in a polycrystal and Bragg-dip is the profile caused by diffraction phenomenon of neutrons in a single-crystal
Bragg-edge transmission spectrum includes bulk crystallographic information averaged over a neutron transmission path in a polycrystalline material, e.g., quantities of each crystalline phase, degree of crystallographic anisotropy, preferred orientation, crystallite size, crystal lattice plane spacing (d-spacing) relating to macro-strain, d-spacing distribution’s broadening relating to micro-strain of each phase
The analyses using the RITS code were performed at each pixel of the imaging detector
Summary
Wavelength-resolved neutron transmission imaging experiments using the time-of-flight (TOF). Bragg-edge transmission spectrum includes bulk crystallographic information averaged over a neutron transmission path in a polycrystalline material, e.g., quantities of each crystalline phase, degree of crystallographic anisotropy (texture), preferred orientation, crystallite size, crystal lattice plane spacing (d-spacing) relating to macro-strain, d-spacing distribution’s broadening relating to micro-strain (relating to dislocation density etc.) of each phase. Bragg-dip transmission spectrum includes bulk crystallographic information along a neutron transmission path in a coarse-grained/single-crystal material, e.g., the number of crystalline grains, crystal orientations of each grain and so on.
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