Real-time, digital imaging of fast neutrons and γ rays with a single fast liquid scintillation detector

Scanning-based methods for the spatial characterization of radioactivity represent an important application of radiation instrumentation. In this paper, the use of a single, fast liquid scintillation detector for this purpose is described which enables radionuclides that emit both γ rays and neutrons to be characterized at the same time, in real-time. This approach combines the use of an autonomous astronomical mount, fast digital mixed-field analyzer and scintillation/high-Z collimator to enable an image of the origin of both neutrons and γ rays to be constructed on-the-fly as the data are detected. The events are detected, digitized, discriminated, logged and assigned to a corresponding component in one of two separate images (either neutron of γ ray) before the eyes of the user. In particular, this technique has potential uses for the environmental characterization of radioactive contamination in nuclear facilities, security applications and in accident response scenarios. The technique complements current, established γ-ray imaging capabilities that rely on inorganic scintillators, to the combined assay of neutron- and γ-ray emitters. This opens up the assessment to neutron-emitting fissile materials and heavy actinides that are susceptible to spontaneous fission. The research is topical since the system is not reliant on now-scarce quantities of ³He and could readily exploit non-hazardous high-flashpoint scintillation liquids. Of particular novelty in this paper is the real-time acquisition of a mixed-field image, improved spatial resolution due to a refined collimator geometry and the characterization of an accelerator-borne field.