Abstract. An investigation is undertaken of the extent to which the Landau and Rumer procedure (1937) for calculating acoustic absorption in dielectrics is invalidated by its assumption that the thermal phonons are in equilibrium. It is shown that this assumption will break down in pure materials at low temperatures for sufficiently high acoustic intensities and frequencies, and that in several such materials at T approximately 10K a substantial change in the 'low intensity' acoustic relaxation time may be expected for intensities approximately 10^-1-10^-2W cm^-2 at frequencies approximately 1 GHz. It is suggested that measurement of this effect could be of use in distinguishing between energy-conserving and non-conserving acoustic interaction processes, and in providing an independent estimate of thermal-phonon relaxation times.

Print publication: Issue 20 (21 October 1974)