  The aim of this article is to show it is possible to get the power spectrum
of the synchrotron radiation from the Volkov solution of the Dirac equation and
the S-matrix. We also generalize the Bargmann-Michel-Telegdi equation for the
spin motion in case it involves the radiative term. This equation can play
crucial role for the spin motion of protons in LHC. The axion production in the
magnetic field described by the Volkov solution is discussed.
