Fast neutron radiography tests at the YAYOI-reactor, university of Tokyo

Abstract Fast neutron radiography (FNR) has been jointly studied by the members of neutron radiography laboratories in Japan by using the CR-39 nuclear track detector at the fast neutron source reactor “YAYOI” of the University of Tokyo. Three beam holes installed at the reactor are utilized, whose collimator ratios, L D , are up to 135, and the fast neutron fluxes are more than 10 6 ncm −2 s −1 . Some well-defined FNR images of various types of objects are obtained with a fast neutron fluence of about 10 10 n/cm 2 . Small holes of 0.5 mm in diameter and 10 mm in depth in an acrylic plate are well imaged through 60 mm thickness of iron plate. Hydrocarbon specimens placed behind thick iron plates (30 mm) are clearly imaged. For the ASTM image quality indicators (IQIs for thermal neutron radiography), very thin A1 spacers with 0.05 mm thickness in the SI indicator have been discernible. The scattering component of fast neutrons from object materials does not seriously degrade the resolution of the FNR image.