Acoustically Modulated Gamma Rays From Fe⁵⁷

The relationship between the emission of γ rays by nuclei bound in a crystal and the creation (or destruction) of phonons has been discussed by Visscher, and suggests that a careful study of the "off-resonance" line shape in a Mossbauer-type experiment may be used to observe the frequency distribution of lattice vibrations in the crystal. Unfortunately, a direct attempt at such a study seems difficult since it requires the measurement of nuclear y-ray absorption cross sections much smaller than the photoelectric cross sections for the same atom. In an attempt to investigate the interactions between phonons and emitting nuclei, therefore, it was decided generate low-energy phonons acoustically, and to study their effect on the γ-ray spectrum.