The design of a constant wavelength ultra small angle neutron scattering spectrometer

In order to carry out the research of constant wavelength ultra small angle neutron scattering spectrometer (USANS), the design principle is studied in this paper base on relevant information from international laboratories. The main components are designed and calculated by using the Simres and NOP codes, and analytic method. The channel-cut crystal for monochromator and analyzer, and the pre-monochromator are designed, and minimum Q of spectrometer is calculated. The results indicate that width of Darwin plat affects the minimum Q of spectrometer, the angle resolution of reflectivity planes selected in the design can ensure a Q resolution in 10-5 order. After the monochromatic neutron guide, a vertical focus monochromator does not seem to increase neutron flux at the sample stage, to simplify the monochromator structure and its manufacturing process, we propose to use un-focus pre-monochromator after the monochromatic neutron guide. (authors)