Optimising visibility for the neutron radiography of titanium and nickel gas turbine components

An analytical expression for the visibility of radiographic images with phase and absorption contrast has been derived. It was used to theoretically optimise the visibility of cracks in titanium and nickel for the case of neutron radiography. The image-to-object distance, object-to-detector distance and the crack depths were varied in the optimisation. The different neutron refractive indices of the titanium and nickel produced qualitative differences in the predicted visibility as a function of the spatial frequencies of the object. Significant visibility from phase contrast was predicted for 50 μm deep cracks in nickel and 200 μm deep cracks in titanium.