Abstract
In poly(methyl methacrylate) glass at temperatures much lower than the glass transition temperature, one observes quadielastic light or neutron scattering. The corresponding relaxation time is short (about 4 × 10−12s) and weakly dependent on temperature. Conversely the intensity of quasielastic scattering is strongly temperature dependent. It is found that this intensity and the mean square displacement due to anharmonic motions have the same temperature dependence as that of the hole volume fraction, which is determined by positron annihilation lifetime spectroscopy. The relation between the slow relaxation, which is responsible for the dynamic hole volume fraction, and the localized fast relaxation, is emphasized.