Dynamic nondestructive inspection of optically opaque systems can be accomplished using a dynamic radiography technique with thermal neutrons as the illuminating radiation. Dynamic radiography correlates the useful information in scattered radiation from vibrating objects. The information generally takes the form of three-dimensional frequency spectra profiles. Such data give the mechanical condition of objects. Thermal-neutron scattering from eccentrically rotating plastic pegs shows that single-point system correlation sensitivity can indicate the presence of pegs in. in diameter. Pulsed polyethylene cube experiments emphasize the effects of object nonrigidity on correlation to show how sensitive dynamic-neutron radiography is to changes in the mechanical quality of nonrigid hydrogenous materials.