Anomalous Recoilless Fraction and Second-Order Doppler Shift in Mössbauer Resonance

Abstract

The observed anomalies in second order Doppler shift (SOD-shift) and recoilless fraction are explained on the basis of the thermal relaxation of a localized mode. A general expression which includes both the SOD-effect and the lattice mode relaxation is derived for the emission probability of Mössbauer radiation. The recoilless fraction is found to be independent of the mode relaxation. A particular class of simple experiments are suggested for the unambiguous evaluation of the thermal relaxation rate of the localized mode.