We compute the single-particle inverse lifetime, along with the
conductivity-derived scattering rate, for a metallic system in an s-wave
superconducting state. When both electron-phonon and electron-impurity
scattering are included, we find that while these scattering rates are in
qualitative agreement, in general quantitative agreement is lacking. We also
derive results for the quasiparticle lifetime within the BCS framework with
impurity scattering, which makes it clear that impurity scattering is
suppressed for electrons near the Fermi surface in the superconducting state.Comment: 46 pages, Postscript figures (to be published in Aust. J. Phys.