Time-of-flight studies of multiple Bragg reflections in cylindrically bent perfect crystals

Multiple Bragg reflections (MBRs) realized in a bent perfect crystal (BPC) slab by sets of different lattice planes behave differently from the case of perfect nondeformed or mosaic crystals. Because of elastic bending (homogeneous deformation), individual sets of lattice planes are mutually in dispersive diffraction geometry and the kinematical approach can be applied on this MBR process. The elastic deformation produced by the cylindrical bending can enormously strengthen the MBR effects, which can then be investigated even at small neutron sources. By using neutron diffraction and the time-of-flight method, carried out at the 45 MeV linac-based pulsed cold neutron source at Hokkaido University, it has been demonstrated that when setting the BPC slabs in the symmetric transmission geometry many strong MBRs accompanying forbidden Si(222) or Si(002) reflections can be observed. The advantage of the time-of-flight method consists in the fact that it is possible to observe not only primary MBRs related to the basic forbidden reflections but also their higher orders, which could be easily separated in the time-of-flight spectra.