Measurement of spin rotation in particle channeling as a means for experimentally testing the correctness of the method for deriving the equation of motion for a spin

Two alternative approaches to deriving the equation of motion for a spin are compared. It is shown that the conventional, approach leads to the conclusion that the spin of a positron is rotated through a large angle as the result of planar positron channeling in a straight crystal. The quantum-mechanical approach based on the Foldy-Wouthuysen transformation predicts no spin rotation in this case. Experimental measurements can reliably discriminate between the two methods for deriving the equation of motion for a spin. (C) 2000 MAIK "Nauka/Interperiodica".