Abstract
Saturation of the 9.4-GHz hypersonic attenuation was observed in crystalline quartz after fast-neutron irradiation. The sample, which exhibits long-range order, shows a low-temperature acoustic behavior similar to that observed in amorphous materials. As in glasses, the results can be explained by the existence of configurational low-energy excitations, with a two-state nature, which were put forward as intrinsic to the amorphous state.