CARACTERISTICS OF COPPER SINGLE CRYSTAL AS A NEUTRON MONOCHROMATOR

A simple formula is given that permits the calculation of the neutron reflectivity from a single–crystal cut along different planes. The monochromatic features of copper single crystal are detailed in terms of the cutting plane, crystal mosaic spread and thickness within the wavelength band from 0.1 up to 0.4 nm. A computer program Cu-MONO written in FORTRAN-77, has been developed to carry out the required calculations. Calculation shows that, 5 mm thick Cu singlecrystal cut along its (111) plane having 0.5° FWHM on mosaic spread are the optimum parameters when, it is used as an efficient neutron monochromator at wavelength 0.114 nm . Moreover the reflected 1st - order neutrons are almost free from the accompanying higher order ones at wavelengths up to 0.15 nm. The same features are of Cu (200) however, with less reflectivity than the later. While Cu (220) is preferred than the others at wavelengths up to 0.18 nm. The calculated integrated neutron intensity of the 1st -order reflection, when the monochromatic wavelength is longer than 0.25 nm, was found to be less than that of higher orders ones from a thermal reactor flux. However, from a cold reactor one, the intensity of the 1st order from Cu (111) within the wavelength band from 0.25 up to 0.4 nm is higher than the later. While, from Cu (200) is up to 0.36 nm, and from Cu (220) is only up to 0.3nm.