Bremsstrahlung asymmetry, R caused by the angular spin momentum transfer
of a bremsstrahlung particle to the photons of an emitted
forward-backward peaking radiation pattern. Momentum transfer from
charged particle to photon could be in the form of bremsstrahlung
particle emitting a photon of higher momentum. Bremsstrahlung particle,
following anticlockwise spiral particle trajectory, has bremsstrahlung
spin in the clockwise direction