Relaxation equation for muonium-like systems with electron spin more than one half

A phenomenological derivation of the Wangsness–Bloch–Redfield equation for the density matrix of muonium-like systems is given in this paper. In the case of the isotropic relaxation, it is shown that the corresponding relaxation term is described by only two independent constants. A typical form of the density matrix of the isotropic hyperfine interaction is given, and it is shown that the density matrix is decomposed into diagonal blocks. Relaxation rates corresponding to the different blocks can differ by orders of magnitude.