  We consider the lifetime of quasi-particles in a d-wave superconductor due to
scattering from antiferromagnetic spin-fluctuations, and explicitly separate
the contribution from Umklapp processes which determines the electrical
conductivity. Results for the temperature dependence of the total scattering
rate and the Umklapp scattering rate are compared with relaxation rates
obtained from thermal and microwave conductivity measurements, respectively.
