On the Mechanism of the Volume Reflection of Relativistic Particles
  The mechanisms of the volume reflection of positively and negatively charged relativistic particles in a bent crystal have been analyzed. It has been shown that the empty core effect is significant for the negatively charged particles. The average reflection angle of the negatively charged particles has been determined and the conditions for the observation of the reflection and refraction are discussed. 
Gennady V. Kovalev
physics.plasm-ph