Neutron topography is an imaging technique which maps the variations of the reflecting power. It has to bedistinguished from neutron radiography (l), which uses the differences in absorption. The topographic techniques (2) were developed in the late fifties and in the sixties, in the X-ray case, mainly to characterize the new crystals produced for the electronics industry, by visualizing the defects (dislocations, twins, precipitates—) present within their volume. They are non destructive and sensitive to very weak distortions(10−7is sometimes observable). Neutron topography started later, in the early seventies (3,4,5), and developed mainly at the high flux reactor of the Institute Laue Langevin. Reviews of the activity in neutron topography are given in references (6) and (7).