Brillouin scattering and attenuation of hypersonic waves in molten NaNO3

Abstract

Brillouin spectra of molten NaNO3 have been investigated at two different scattering angles, 40° and 140°, in a temperature interval ranging from 310° to 450 °C. The measured frequency shifts and linewidths of the Brillouin components were used to determine the hypersonic velocity and attenuation of thermal waves in the frequency range 3.4–10.2 GHz. The determination of the Brillouin linewidths has been performed using a convolution technique, necessary when narrow linewidths are to be determined. The hypersonic velocity measurements show no appreciable dispersion compared either to ultrasonic data or to each other. In the line broadening measurements, however, the attenuation shows some dispersion especially at the higher frequencies, thus indicating that the measurements are performed at frequencies just below a relaxation frequency. A calculation of this frequency using a theory with a single relaxation time confirms this assumption. Subject Classification: [43]35.24; [43]35.30