Design and expected performance of a thermal neutron imaging facility at the N. C. State University PULSTAR reactor

A thermal neutron imaging facility has been set up at the North Carolina State University PULSTAR reactor. The PULSTAR is an open pool type light water moderated 1-MWth research reactor with six beam tubes. The present facility is set up on beam tube # 5 of the reactor. The facility is intended to have radiographic and tomographic capabilities. The design of the neutron collimator was performed using MCNP5. The collimator includes a 4-inch bismuth filter followed by a 6-inch single-crystal sapphire filter. Thermal neutron scattering cross-section libraries for sapphire and bismuth were generated and used in the MCNP simulation of the system. Based on the current design, the L/D of the facility ranges between 100 and 150. The neutron flux can be varied from 1.8times10⁶ to 7times10⁶ n/cm²-sec with a Cd-ratio of ~450. The resolution of the system for different imaging media was also estimated and found to be ~30 mum for conventional radiography films and ~110 mum for digital image plates. Initial radiographs using film and image plates are presented. According to ASTM standards, the imaging facility achieves a beam quality classification of I^A