Gamma-ray Imaging Results From The International Partnership For Nuclear Disarmament Verification Belgium Exercise

We describe the performance of a novel gamma-ray imaging system when imaging nuclear fuel as part of an International Partnership for Nuclear Disarmament Verification (IPNDV) exercise hosted by SCK-CEN in Belgium. The single pixel gamma ray imager is designed around the theory of compressed sensing and utilises a CLLBC scintillator detector that can detect both gamma rays and neutrons. In its current configuration the imager can identify and localise gamma emitting radiation and detect the presence of neutron radiation. The detection, localisation and identification of radiation can provide added confidence for nuclear disarmament verification. In these results, the measured gamma ray images are overlayed with an optical image, which enables the end user to easily visualise where the radiation is coming from. Traditional gamma ray imagers (e.g. Compton camera, pinhole camera, coded aperture camera) typically have a limited energy range and/or a limited field of view. However, the described imager is able to identify and localise gamma emitting radiation over a large field of view (360° x 90°) and across a wide energy range (40 keV to 3 MeV). The imaging results from measuring shielded and unshielded MOX fuel will be presented. The imaging system identified and localised the nuclear material gamma emissions and also detected the presence of neutrons. The effects of shielding the fuel assembly are seen to hide the localisation information for low energy gamma emissions. However, the imaging of higher energy gamma emissions is able to reveal the full localisation information. Two imaging systems were subsequently setup at 90° to each other (relative to the fuel assembly), which enabled the location of the nuclear fuel to be further confined within the facility. As the technology confirms the presence of nuclear material in the fuel assembly location, it is also confirming the absence of nuclear material being contained elsewhere within the facility room.