  The possibility of propagation of second sound waves in diamond single
crystals depending on their dimensions, concentrations of isotopes and
temperature is studied. At this correct account of phonon scattering on
boundaries is important. The calculation of phonon collision frequencies is
carried out in the reduced isotropic crystal model using second and third
modules of elasticity and in Callaway model on the basis of experimental data
on diamond thermal conductivity. Both models give us the consistent values of
parameters under which the propagation of SSW is possible. It is discovered
that concentrations of isotopes 13C < 10-5, temperatures T < 90K. Such a good
agreement provides the reliability of received results and shows the efficiency
of reduced isotropic crystal model in the description of diamond properties in
low temperature range.
