Measurement of Thermal Diffuse Scattering Using Pulsed Neutron Diffraction

Abstract

Collective excitations in crystals can be examined with neutrons by means of the so-called 'diffraction method', without carrying out an energy analysis of the inelastically scattered neutrons. For studying thermal diffuse scattering (I'DS) from acoustic phonons, it is particularly advantageous to employ a white source of pulsed neutrons instead of a monochromatic source of reactor neutrons. Provided that the neutron velocity is less than the sound velocity in the crystal, each reciprocal-lattice point observed in backscattering Laue geometry is associated with a wavelength window within which TDS is forbidden. The edges of the window are readily measured to give the sound velocity as a function of the direction of propagation.