Performance of a double crystal diffractometer with different channel-cut perfect Si crystals

The double crystal diffractometer (DCD) at the Geesthacht Neutron Facility (GeNF) is equipped with triple-bounce channel-cut perfect Si(111) crystals. In this way the intrinsic background of DCD, i.e. given by the rocking-curve wings, has been decreased dramatically. Its former dependence on the scattering vector q of q(-2) was changed to q(-6). An observed deviation from the q(-6) behaviour is possibly attributed to neutrons propagating and diffracting inside the walls of the channel-cut crystals. In order to reduce this parasitic intensity and for further improvement of DCD with respect to higher sensitivity to weak sample scattering quintuple-bounce side grooved channel-cut crystals have been used. The change in the rocking curves without and with inserting cadmium in the grooves of the walls is pointed out. The efficiency of DCD is shown in the case of neutron scattering from Latex spheres with radii of about 2200 nm. (C) 2000 Elsevier Science B.V. All rights reserved.