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 role is played by the method used to clean the crystal surfaces that the particles beam encounters first. It was experimentally observed that chemical cleaning of the surfaces via etching leads to better performance than conventional mechanically treated samples do. We investigated the physical reasons for such a behaviour through characterization of the surfaces of the crystal. We observed that mechanical 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 critical angle of relativistic particles for channeling, i.e., it acts like an amorphous layer.