NEUTRON MICROFOCUSING WITH BENT CRYSTALS

The strong focusing of neutron beams by reflection from two bent crystals in antiparallel (+, +) setting is discussed. A previous analysis made for thin perfect crystals is extended, by numerical computations, to the case of a thick and mosaic first crystal. It is concluded that microfocusing is also achievable with flat mosaic first crystals. The combination of strong beam focusing onto sample with narrow diffraction lines in a given limited range, which is a requirement in stress scanning, is further examined. Results of test measurements, with a flat mosaic thick silicon as a first crystal and pneumatically bent thin silicon as a second crystal, are presented. The strong focusing of the beam onto sample is confirmed to be compatible with the focusing in scattering. The feasibility of microfocus diffraction on existing three-axis instruments with flat mosaic monochromators is also confirmed. Techniques for plastic bending of high-reflectivity crystals will have to be developed to take full advantage of microfocusing.