Double crystal diffractometer arrangement for very small angle neutron scattering with PNO in JRR-3M

The status of a double crystal diffractometer (DCD) for very small angle neutron scattering (VSANS), which is arranged in the precise neutron optics (PNO) apparatus on 3G beam hole at JRR-3M, is presented. The DCD consists of nondispersive (1,1) setting of perfect silicon single crystals with a sample between two crystals and is set in a constant temperature chamber. The first crystal is set on a normal goniometer and acts as a horizontal beam collimator. The second crystal is set on a precise goniometer of which the smallest control step size is 5 x 10-3 sec of arc, and acts as an analyzer for VSANS. The 111 symmetric reflection is used for both crystals. A measurement of silica spheres reveals that the q-range is available between 2 x 10-4 and 3 x 10-2 mm-1, which covers up to μm in real space. (author)