  The spin light of neutrino is considered in the process of a neutrino
radiative transition between two different mass states in presence of medium.
By this study we investigate the influence of background matter on the initial
and final neutrino states in the process of massive Dirac neutrino decay due to
the non-zero transition magnetic moment. We derive corresponding corrections to
the total width of the process over the matter density in most important for
applications cases.
