Abstract
Brillouin-scattering measurements on acoustoelectrically amplified flux are used to determine the room-temperature frequency dependence of the lattice attenuation of ultrasonic shear waves in CdS up to a frequency of 7 GHz. The results show clearly a transition from the Akhiezer f2 regime to the Landau-Rumer f1 regime. The transition frequency provides an estimate of about 35 psec for the average lifetime of the thermal phonons involved in the ultrasonic attenuation process.