Abstract
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.
Highlights
Global imperatives to decarbonise electricity supplies have resulted in a variety of new nuclear build programmes and related developments in nuclear fuel technology
The measurement zone features the three-layer detectors assembly as described above, the front-end electronics associated with the detection layers, and the three power supplies that provide the 29.4 V DC required by the silicon-based photomultiplier (SiPM)
The high sampling speed of the Agilent 54845A Infiniium Oscilloscope allows the digitising of EJ-204 pulses and the plotting of the pulses shown in Figure 5, the low input impedance (1 MΩ) can cause the undershooting observed in the EJ-204 pulse, which might affect further analysis on pulse shape discrimination
Summary
Global imperatives to decarbonise electricity supplies have resulted in a variety of new nuclear build programmes and related developments in nuclear fuel technology. Of key strategic importance in this regard is the deployment of detection technologies capable of identifying and tracking special nuclear materials at national and international cross points, ports and borders [3, 4] These areas can be either controlled (e.g., associated with secure areas within airports, border and cargo inspection points etc.) or uncontrolled (e.g., at airport terminals, train stations and so forth). The main features of this design are: The prototype front-end is highly compact, having dimensions of 200 mm x 120 mm x 120 mm and a mass of 3 kg When battery powered, this allows the instrument to be utilised at any stage during the monitoring protocols of radioactive and nuclear materials at national and international cross points, ports and borders. The development of Pulse Shape Discrimination (PSD) techniques to be used with this instrument are to be discussed in future work
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