High Resolution Combined Neutron/X-ray Imaging Detector

Abstract

Federal agencies including DOE (NNSA), CWMD, and DTRA all play a vital role in the U.S. government's efforts to prevent, counter, and respond to a terrorist or other adversary with a nuclear or radiological device. To support its functions and foundational capabilities across nonproliferation, counterterrorism, and emergency response mission areas, these agencies need advanced sensors and instrumentation that may be used to rapidly identify threats and get the information needed to plan a response. At RMD we are developing the tools and techniques that will address some of these mission needs. One ongoing effort involves the development of a portable, high spatial resolution, combined neutron/X-ray radiography detector. The detector is capable of high sensitivity imaging of fast neutrons, thermal neutrons, and high energy X-rays, and will permit data analysis for material identification purposes. The key enabling technology for such a detector is the fabrication of a large area scintillator converter that can simultaneously detect fast neutrons, thermal neutrons, and hard X-rays, with the highest possible efficiency. To preserve spatial resolution the scintillator is microstructured to minimize the traditional trade-off between the detection efficiency and spatial resolution. Additionally, the scintillator should be sufficiently bright for enhanced signal-to-noise-ratio (SNR), and its fabrication method should be amenable for producing large area sensors. We are investigating several approaches to realize such sensors. Here, we report preliminary results on a portable flat panel based large area detector measuring 25 cm × 30 cm in active imaging area, and an intrinsic spatial resolution of 139 µm. The report also includes scintillator design approaches, GEANT4 simulations of scintillator response to various radiation types, and experimental imaging data taken using thermal neutrons, fast neutrons between 1 MeV to 40 MeV, and hard X-rays up to 400 kV. The performance of the detector as a whole has been evaluated at ORNL and NIST neutron beam lines.