PARASITIC NEUTRON BRAGG-REFLECTIONS FROM LARGE IMPERFECT SINGLE-CRYSTALS

A formula is given which allows to calculate the contribution of the t otal Bragg scattering from different (hkl) planes to the neutron trans mission through a large imperfect single crystals. The formula takes i nto account the crystal structure type, its mosaic spread value, the p lane along which the crystal surface is cut along and its orientation with respect to the neutron beam direction. A computer program ISCANF- 1 was developed to calculate the total parasitic scattering cross-sect ion from different (hkl) planes as well as the nuclear and diffuse sca ttering cross-sections. The ISCANF-1 program was applied to calculate the neutron attenuation through Cu and Zn single crystals, each of the m cut along (002) planes. The calculated values of the neutron transmi ssion through Cu and Zn crystals were compared with the measured ones in the wavelength range 0.21-0.47 nm and 0.04-0.52 nm respectively. Th e measured and calculated values were found to be in reasonable agreem ent within the statistical accuracy. The computer program ISCANF-1 was also applied to investigate the effect of parasitic Bragg scattering on the neutron filtering characteristics of both Zn and Cu single crys tals as a function of their physical parameters. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.