Attenuation and dispersion of longitudinal acoustic waves in α-sulphur

Velocities and attenuations of longitudinal acoustic waves propagating along the three principal directions of α-sulphur were measured by means of ultrasonic waves between 20 and 500 MHz and by Brillouin scattering between 4 and 25 GHz. Velocity and attenuation variations plotted versus frequency are continuous along the whole investigated range 20–25 000 MHz. Besides, an important velocity dispersion has been pointed out, with a relative variation of about 1.5%. A phenomenological interpretation involving a loss process with a single relaxation time is given which allows us to account for the whole set of results.