Investigation of coded source neutron imaging at the North Carolina State University PULSTAR reactor

A neutron imaging facility is located on beam-tube #5 of the 1-MWth PULSTAR reactor at the North Carolina State University. An investigation has been initiated to explore the application of coded imaging techniques at the facility. Coded imaging uses a mosaic of pinholes to encode an aperture, thus generating an encoded image of the object at the detector. To reconstruct the image recorded by the detector, corresponding decoding patterns are used. The optimized design of coded masks is critical for the performance of this technique and will depend on the characteristics of the imaging beam. In this work, Monte Carlo (MCNP) simulations were utilized to explore the needed modifications to the PULSTAR thermal neutron beam to support coded imaging techniques. In addition, an assessment of coded mask design has been performed. The simulations indicated that a 12 inch single crystal sapphire filter is suited for such an application at the PULSTAR beam in terms of maximizing flux with good neutron-to-gamma ratio. Computational simulations demonstrate the feasibility of correlation reconstruction methods on neutron transmission imaging. A gadolinium aperture with thickness of 500 μm was used to construct the mask using a 38 x 34 URA pattern. A test experiment using such a URA design has been conducted and the point spread function of the system has been measured.