Solution of the Pauli-equation for neutrons in varying magnetic fields and its application to reflection and transmission at helical magnetic structures

The behaviour of neutrons in magnetic fields varying harmonically in time or space is treated. For the case of time-dependent fields the movement of the spins is followed in detail. For the case of helical fields the general solution of the Pauli-equation is given. It is shown that for neutrons a helical B-field is representing a medium with quite general properties of double-refraction. The formal connection between the solutions for both cases of the field is discussed. The results are applied to the reflection and transmission of neutrons at helical structures. It is shown that a critical angle exists corresponding to the angle of total reflection, but being greater than this and increasing with increasing helicity. A further main consequence of the helix field is that always a part of the reflected wave has flipped spins its intensity depending on the polarization of the incident wave.