Three-Phonon Processes in Second Sound, Poiseuille Flow, and Thermal Conduction in Solid 4He

Poiseuille flow and second sound have provided for solid 4He a body of evidence concerning τN-1, the N-process scattering rate, τN-1 has also been inferred from the thermal resistivity of isotopic point defects. However, the various estimates of τN-1 differ both as regards temperature dependence and the absolute magnitude [1]. Recent Poiseuille flow experiments of Golub et al [2] point to differences in dislocation concentration in the helium crystals as a source for these disparities. In their analysis, allowing for dislocations increases the overall estimate of τN-1 and changes its apparent temperature dependence from (T/θ)3 to (T/θ)5. We have looked again at the pulse propagation of second sound in solid 4He to see what evidence there might be for the effects of dislocations.