Sokolov-Ternov Effect

The Sokolov-Ternov effect is the effect of self-polarization of relativistic electrons or positrons moving at high energy in a magnetic field. The self-polarization occurs through the emission of spin-flip synchrotron radiation. The effect was predicted by Igor Ternov which then were rigorously justified by Arsenij Sokolov using exact solutions to the Dirac equation. An electron in a magnetic field can have its spin oriented in the same or in the opposite direction with respect to the direction of the magnetic field (which is assumed to be oriented 'up'). The 'spin down' state has a lower energy than 'spin up' state. The polarization arises due to the fact that the rate of transition through emission of synchrotron radiation to the 'spin down' state is slightly greater than the probability of transition to the 'spin up' state. As a result, an initially unpolarized beam of high-energy electrons circulating in a storage ring after sufficiently long time will have spins oriented in the direction opposite to the magnetic field.