Focusing double bent crystal (DBC) diffractometer for medium-resolution small-angle neutron scattering (SANS) experiments

A new modification of a focusing SANS instrument where at least the first crystal is set for diffraction in the asymmetric transmission geometry is presented. Unlike an earlier version which employed both crystals in the symmetric Bragg-case geometry [Kulda & Mikula (1983). J. Appl. Cryst. 16, 498-504], the new modification permits one simultaneously to exploit the effects of natural wavelength focusing and space condensation of the diffracted beam due to asymmetric diffraction. This DBC instrument seems to be suitable for use with beams with a large cross section at the first crystal and for SANS experiments on samples with a small width (few mm).