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Neutron Diffraction

Introduction

Neutron diffraction provides similar structural information as electron diffraction. Neutron beams interact more strongly with nuclei than do X-rays and neutron diffraction is more useful than X-ray diffraction for determining proton positions. The two main uses of neutron scattering are in refining molecular structures that have been mostly determined by X-ray diffraction and in polymer characterization using small-angle neutron scattering (SANS).

Neutrons interact with a solid to a much lesser degree than X-rays and therefore have advantages in studying materials that are damaged by X-rays and in cases where a large penetration depth is desired. For the three types of diffraction methods, neutrons are unique in that they have a magnetic moment and are therefore sensitive to magnetic ordering in a solid.


Instrumentation

Neutrons are produced by fission reactions in a nuclear reactor or by irradiating a metal target with high-energy protons from an accelerator, which is called spallation. Reactor sources produce a continuous spectrum of neutron energies and require a monochromator crystal to select a particular energy. Accelerator sources are usually operated in a pulsed mode and neutron wavelength is selected by time-of-flight methods, that is, data is taken at a fixed Bragg angle as a function of neutron energy. Multiple detectors are used to take data at different angles in parallel to speed data acquisition.


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