Design and performance of a thermal neutron imaging facility at the North Carolina 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 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-in bismuth filter followed by a 6-in 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 at the image plane can be varied from 1.8 x 10(6) to 7 x 10(6) n/cm(2).s with a Cd-ratio of similar to 450. The resolution of the system for different imaging media was also estimated and found to be similar to 33 mu m for conventional radiography film and similar to 110 mu m for digital image plates. Initial measurements, using ASTM standards, show that the imaging facility achieves a beam quality classification of I-A.