High-Resolution Diffraction using Larmor Precession of Polarised Neutrons

摘要

A new neutron diffraction method is introduced which enables high-reslution diffraction without he confinement of a highly collimated beam, necessary in coventional highresolution neutron diffraction. To achieve this, Larmor precession of a polarised neutron beam is used to label each neutron of the incident and scattered neutron beam with its wavelength and scattering angle. Using a Larmor precession device with front and back faces inclined over an angle adjusted to the diffraction angle, the relation between wavelength and transmission angle of the Larmor modulator matches precisely the relation between wavelengtha nd scattering angle of the Bragg reflection. In this way a lattice constant is determined with an accuracy that only depends on the precession angle in the precesson device, while using a low-resolution beam. A determination of the lattice constants with relative accuracy of the order of 10~(-6) is expected to be feasible, while using a fully divergent neutron beam with a low wavelength resolution, which means an effective intensity gain of orders of magnitude.