NEUTRON MICROFOCUSING WITH BENT CRYSTALS

The strong focusing of neutron beams by reflection from two bent cryst als in antiparallel (+, +) setting is discussed. A previous analysis m ade 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 diffractio n lines in a given limited range, which is a requirement in stress sca nning, is further examined. Results of test measurements, with a flat mosaic thick silicon as a first crystal and pneumatically bent thin si licon as a second crystal, are presented. The strong focusing of the b eam onto sample is confirmed to be compatible with the focusing in sca ttering. The feasibility of microfocus diffraction on existing three-a xis instruments with flat mosaic monochromators is also confirmed. Tec hniques for plastic bending of high-reflectivity crystals will have to be developed to take full advantage of microfocusing.