Phase contrast neutron imaging at a medium intensity neutron source

Neutron Imaging is a technique for the nondestructive testing (NDT) of materials. It is characterized by its sensitivity to materials composed of low atomic number (Z) elements such as hydrogen. Enhancement of the spatial resolution and the contrast of the obtained images are primary objectives that are continuously being pursued in the development of this technique. An approach of improving the contrast at the material edges of a sample is non-interferometric phase contrast neutron imaging, which has been demonstrated at the start of this decade. Since then it has been performed at multiple facilities located at high flux neutron sources. However, due to its physical requirements (e.g., the use of pinhole apertures), the applicability of this technique remains primarily limited to such high flux facilities. Consequently, to expand its utilization in NDT applications, its performance at low and medium intensity neutron sources, that are available around the globe, should be explored. In this work, the feasibility of performing phase contrast neutron imaging at the North Carolina State University PULSTAR reactor was studied. The 1-MW PULSTAR represents a prototypical medium flux neutron source. It is demonstrated that phase contrast imaging can be successfully implemented if careful attention is given to tailoring the neutron beam with the objective of maximizing the thermal neutron flux (and content) while minimizing the gamma-ray and fast neutron noise. Results are presented of imaging exercises demonstrating the phase contrast concept using a Fuji BAS-NDG image plate detector.