Relaxation-time analysis of second-sound data in NaF

In an earlier paper, starting from the phonon Boltzmann equation, expressions were derived which give velocityc ₂ and damping of second sound in a Debye solid in terms of mean relaxation times for various scattering processes. Using those results, heat-pulse data showing second sound in NaF were analyzed. The experimental values ofc ₂ (T) can only be reproduced if \(\bar \tau _N^{ - 1}\) , the mean relaxation rate for normal phonon collisions, varies with temperature asT ³. The mean Umklapp collision time also shows some unexpected behavior.