LATTICE DYNAMICAL ASPECTS OF MOSSBAUER PARAMETERS

Abstract

Like the optical and acoustical resonance, Mbssbaaer effect may be defined as recoilless gamma resoncknce (emission, absorption or scattering) i.e, no part of the energy is expended in the recoil of the nucleus emitting or absorbing the gamma quanta. The probability f for the emission of gamma rays from radio-active atoms without energy exchange with the lattice. vibrations of the crystal in which these are embedded, depends upon the strength of the interatomic forces between these atoms and the crystal. In this way Mossbauer effect offers a unique tool in its ability to look upon an•imputity atom selectively.Precision measarements of the temperature dependent If' yield the temperature dependence of the mean square displacement of the atom <x2> along the direction of gamma ray emission, \ X2 > through the relation, f = exp(° -1). Another dynamical - X parameter of great significance is the mean square velocity (v2) of the Rbssba )r atom which contributes partly to the shifts of the emission and absorption lines. The different lattice dynamical aspects which can profitably be studied from these parameters include: phonon spectl-a.corteadtrep 0.1 +We atomic biln.d.int forces, anharmonicity of the motion of the vibrating atom, .