Measurements of the frequencies of the normal modes of magnesium

The normal modes of magnesium have been investigated by means of the inelastic scattering of slow neutrons. The frequencies of about 1000 phonons have been measured with a time-of-flight apparatus, and the values along symmetry directions obtained by an interpolation method. Previous workers have found that their results could be fitted by force models extending to fourth-nearest neighbours or less. The present measurements cannot be fitted by any tensor force model extending only to fourth-nearest neighbours. The motions of the atoms for a simple force model are discussed.