Gamma In Addition to Neutron Tomography (GIANT) at the NECTAR instrument

Abstract

The NECTAR instrument provides access to thermal and fast neutrons which are suitable for non-destructive inspection of large and dense objects. Scintillators are used in combination with a camera system for radiography and tomography. Gamma-rays are produced as inevitable by-products of the neutron production. Furthermore, these gamma-rays are highly directional due to their constraint to the same beam-line geometry and come with similar divergence as the neutrons. We demonstrate how these gamma-rays, previously treated as beam contamination can be used as a complementary probe. While difficult to shield, it is possible to utilize them by using gamma sensitive scintillator screens in place of the neutron sensitive scintillators, viewed by the same camera based detector system. The combination of multiple probes often provides complementary information that can result in a better contrast or insight into the sample composition, for a broader range of materials and applications. Hence dual-mode imaging, combining thermal/cold neutrons with X-ray imaging has been developed at many neutron facilities. With X-rays limited in penetration of dense materials to millimeters only, we present a multimodal imaging technique that is capable of penetrating cm-sized objects using thermal to fast neutrons with the addition of gamma-rays by changing the combination of scintillator and beam filter used at the NECTAR instrument.