The scattering of thermal neutrons by crystals

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Abstract
The present article describes some experiments with thermal neutrons to investigate a variety of properties of crystals. Elastic scattering of the neutrons, like Bragg scattering of X-rays, helps to determine the atomic structure of crystals, and is particularly useful for locating light atoms, such as hydrogen, where X-rays fail. It also gives information on the arrangement of electron spins and the density distribution of unpaired electrons in magnetic atoms. Measurement of the change in energy of the neutrons in inelastic scattering gives the frequencies of the normal modes of vibration of the crystal, which are related to the interatomic forces. For magnetic crystals, inelastic scattering also gives the frequencies of spin waves, which depend on the magnetic interactions between the atoms. The article concludes with an account of the experimental techniques of thermal neutron scattering.