Abstract
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 m was used to construct the mask using a 38 ×
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.
