Spin-exchange and dipole relaxation rates in atomic hydrogen: Rigorous and simplified calculations

We calculate the magnetic field and temperature dependence of the rates for all two-body spin-exchange and dipolar transitions among hyperfine levels in cryogenic H gas by means of the coupled-channels method. A description of this method and its practical application is presented. A simple interpretation of the rates is given, in some cases with associated simple closed-form formulas, based on the degenerate-internal-states approximation.