A fast and portable imager for neutron and gamma emitting radionuclides

Here a novel, real-time, highly-compact imaging system capable of detecting and localising gamma rays, thermal and fast neutrons is reported. The imaging system presented in this research comprises of a front-end containing three detection layers with a unique combination of scintillators optimised for multi-particle detection, and backed with silicon photomultiplier diode arrays to enable source localisation and to maximise efficiency. The system exploits Compton and neutron scattering techniques simultaneously to constitute a dual-mode radiation camera. Application-specific software algorithms are implemented here to process the numerous signals from the system and to reconstruct the location of radioactive sources using a back-projection technique. The three front-end detection layers fit within a volume of 120 mm × 120 mm × 200 mm, offering a uniquely compact imaging solution. A prototype of the instrument and the associated electronics have been designed using Monte Carlo simulations, and tested with Cs-137 (given its singular gamma-ray component) and Cf-252 (for its mixed neutron and gamma-ray emission). Experimental results indicate that the system can detect and localise both gamma-ray and neutron sources successfully, with intrinsic efficiencies in the order of 10⁻⁴. All results have been achieved within a scan time of 60 s and with a further data processing time of less than 60 s, for gamma sources of ∼300 kBq and neutron sources of 10⁶neutrons per second (total) in close proximity (<300 mm). Whilst high-speed, mixed-field, particle-imaging systems have numerous applications within both nuclear and non-nuclear fields; this particular system has been optimised for use within the areas of nuclear materials assay and proliferation prevention.