Electromagnetic radiation from an uncharged spin 1/2 particle with an
anomalous magnetic moment moving in the classical electromagnetic external
field originates from quantum spin-flip transitions. Although this process has
a purely quantum nature, it was observed for certain particular external field
configurations that, when quantum recoil is neglected, the radiation power
corresponds to the classical radiation from an evolving magnetic dipole. We
argue that this correspondence has a more general validity in the case of an
unpolarized particle and derive a general formula for radiation in terms of the
external field strength and its derivatives. A classical dynamics of the spin
is described by the Bargmann-Michel-Telegdi equation.Comment: 6 pages,latex, v2, typos correcte
