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-cur ve wings, has been decreased dramatically. Its former dependence on the sca ttering 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 diff racting inside the walls of the channel-cut crystals. In order to reduce th is parasitic intensity and for further improvement of DCD with respect to h igher sensitivity to weak sample scattering quintuple-bounce side grooved c hannel-cut crystals have been used. The change in the rocking curves withou t and with inserting cadmium in the grooves of the walls is pointed out. Th e efficiency of DCD is shown in the case of neutron scattering from Latex s pheres with radii of about 2200 nm. (C) 2000 Elsevier Science B.V. All righ ts reserved.