THE NEUTRON REFLECTIVITY OF BeO, MgO and ZnO SINGLE- CRYSTALS

The monochromatic features of BeO, MgO and ZnO single-crystals are discussed in terms of orientation, mosaic spread, and thickness for efficient neutron reflectivity within the wavelength band from 0.05 up to 0.5 nm. A computer program MONO, has been developed to carry out the required calculations. Calculations shows that, 5 mm thick of BeO single-crystal cut along its (002) plane having 0.5^0 FWHM on mosaic spread has the optimum parameters when it is used as a neutron monochromator. Moreover, the 1st -order monochromatic neutrons are almost free from the accompanying higher order ones at wavelengths shorter than 0.24 nm. The same features are of ZnO (002) with less reflectivity than the former. Also, MgO cut along its (200) plane is preferred than the others at wavelengths shorter than 0.18 nm only. When the selected monochromatic wavelength is longer than 0.25 nm, the neutron intensities of higher orders from a thermal reactor flux are higher than those of the 1st - order ones. For a cold reactor flux, the 1st order of BeO and MgO single-crystals is free from the higher - order ones up to 0.4 nm, while of ZnO is at wavelengths up to 0.5 nm.