Speaker
Dr
Javier Santisteban
(Centro Atomico Bariloche)
Description
After passing through a single crystal, a polychromatic neutron beam presents a series of dips in intensity at specific wavelengths, due to neutrons removed from the beam as a result of Bragg reflection on the crystal planes. These reductions in intensity can be exploited as a contrast agent on wavelength-dependent neutron imaging of single crystal components, or objects having microstructures close to that of a single crystal.
The position, width and depth of those dips depend on the material, the crystal orientation and the degree of perfection of the single crystal. Real monocrystalline solids of macroscopic size present always some degree of imperfection, with slightly misaligned regions ranging from seconds of arc for perfect crystals to tens of minutes for mosaic crystals.
Here we will discuss details of the wavelength dependent transmission of monocrystalline objects, presenting some analytic expressions for the total cross section. Typical widths and depths of the signal for different materials are considered. Possible information to be extracted from such signal (crystal orientation, elastic strain, misorientation) is exemplified through experiments performed in Cu mosaic crystals [1].
Finally, we show recent theoretical advances towards describing the transmission of textured polycrystalline materials as a sum of contributions from many individual single crystallites.
[1] J.R. Santisteban, (2005) Journal of Applied Crystallography. 38, 934–944.
Summary
The wavelength dependence of the neutron transmission of monocrystalline solids is discussed, for different degrees of crystal perfection. Analytical expressions for the total cross section are compared to time-of-flight transmission experiments performed on the ENGIN-X beamline, at Isis, UK.
Primary author
Dr
Javier Santisteban
(Centro Atomico Bariloche)
Co-author
Ms
Florencia Malamud
(Centro Atomico Bariloche)
