The Dirac equation for both electron and positron moving under planar channeling condition was considered. The influence of projectile's spin on the bound energy levels of transverse motion was estimated within analytical approach. The estimates show that for ultra relativistic projectiles and for variety of crystals the presence of a spin results in a small splitting of a bound energy level. This effect, in principle, can be revealed by the use of precise techniques.
A. et al. (Mon,) studied this question.