Contrast mechanisms for neutron radiography

The use of thermal neutrons in contact radiography and tomography [Schlenker and Baruchel, Physica B 137, 309 (1986)] provides a powerful nondestructive analysis technique for materials that are difficult to study with x rays [Kirz et al., Quart. Rev. Biophys. 28, 33 (1995)]. Since x rays are strongly absorbed by the heavier elements and neutrons are preferentially scattered by light elements, neutron radiography is well suited to the visualization of light elements in the interior of metallic objects. In this letter, we demonstrate neutron radiography using a number of different contrast mechanisms. We find we are able to obtain radiographs showing features hitherto unobservable.