  The general expression of the Stern-Gerlach force is deduced for a charged
particle, endowed with a magnetic moment, which travels inside a time varying
magnetic field. Then, the energy integral of the Stern-Gerlach force is
evaluated in the case of a particle crossing a TE rf cavity with its magnetic
moment oriented in different ways with respect as the cavity axis. We shall
demonstrate that appropriate choices of the cavity characteristics and of the
spin orientation confirm the possibility of separating in energy the opposite
spin states of a fermion beam circulating in a storage ring and, in addition,
make feasible an absolute polarimeter provide that a parametric converter
acting between two coupled cavities is implemented
