Morphological and structural studies of crystals for channeling of relativistic particles.

Channeling of relativistic particles through a crystal may be useful for many applications in accelerators. It has been experimented that significant roles are played by the method used to clean the crystal surfaces that the particles beam encounters first. It is exptl. obsd. that chem. cleaning of the surfaces via etching leads to better performance than conventional mech. treated samples do. The authors investigated the phys. reasons for such a behavior through characterization of the surfaces of the crystal. They obsd. that mech. dicing causes a superficial layer rich in dislocations and lattice imperfections, extending tens of microns into the crystal, which is removed via etching. Such a disordered layer is the first portion of the crystal experienced by the incoming particles and results in a mosaicity degree that exceeds the crit. angle of relativistic particles for channeling, i.e., it acts like an amorphous layer.