Advanced Compton-geometry gamma radiation imaging for radionuclide measurement in soils and geomaterials

The continued releases of radioactive material from the earthquake-damaged Fukushima Dai-ichi nuclear power station in Japan, with the risks to water, coastal environments, agricultural land, animals and human health have drawn international concern. The incident, together with the Chernobyl disaster a generation earlier, has highlighted the importance of being able to detect, measure and monitor radiation in our environment. This is no easy challenge - the amounts of radioactivity are often low (relative to controlled medical or industrial settings) or highly dispersed through soils, sediments and water. There is also a considerable background radiation all around us, not only from the legacy of human nuclear technology but from natural minerals, gases (eg. radon, a major problem in some regions), cosmic and solar sources. On the other hand, this radioactivity is used widely by earth and environmental scientists to date rocks, monitor sediment movement and geomorphological changes, or the growth rates and life histories of plants and animals.

If we are to measure environmental radioactivity, not just to help clean-up and recovery after an accidental release but also to monitor sites, prevent releases and support the safe operation and decommissioning of nuclear facilities (as well as support that range of scientific research needs), then we need continuous improvement of sensors which can detect and quantify radiation sources to higher resolution, lower detection thresholds and shorter measurement times.

The current generation of sensors is based on mechanical collimators, a technology similar to the 'pixellated' image sensors in digital cameras, in which the radiation arriving at any point on the surface is used to build up a 2D image of the radiation source. Nuclear physicists at the University of Liverpool have recently developed a new approach for detection of gamma radiation called Compton-geometry imaging. In this approach, two sensors are placed one in front of the other and the measurement is based on the scattering of radiation between them. The technique is powerful because the position of the radiation source is located by mathematically reconstructing the origin of many scattering events, rather than by the physical position of the incident radiation on the collimator surface. This 'electronic' collimation can resolve the position of the source with much greater accuracy and sensitivity than mechanical collimation, has the advantage of being able to locate the source in 3D, and yields smaller, lighter detector equipment with potential savings in measurement time. Currently, only two other research groups in the world are working with this technology.

The objective of this proposal is to understand how this powerful new technology can be optimised for environmental gamma radioactivity measurements. Research so far has focused on the development of prototype Compton cameras for industrial and medical applications, which present very different challenges to the environmental conditions described earlier. By combining a world leading expertise in device development in close collaboration with academic and industry end-users in environmental science and engineering, this Technology Proof-of-Concept proposal aims to develop design criteria, optimised system specifications, and a first prototype for a Compton camera which we intend will set a benchmark for the next generation of environmental radioactivity sensors. Imagine being able to locate a radioactive substance beneath the ground and monitor how it moves with changes in water flow or sediment movement. Or to watch, using a portable device, in real-time how plants and animals take up radioactive materials from contaminated soils and move them into the food chain. Star Trek science? Perhaps for now, but the environmental Compton camera that is the long-term goal of this research project moves us a significant step closer towards that vision.

Stakeholders and Industry
Stakeholder organisations and groups will benefit from development of new technology areas with potential commercial benefits and the promise of higher-quality data to support more reliable models and decision-making tools to improve the effectiveness of policy decisions and post-incident management. Although the proposed project is short-term and proof-of-concept, there are a range of longer-term beneficiaries whose contact with the project will include:
(i) Project partner NNL (Letter of Support), through close engagement with the development of novel environmental Compton imager technologies; bilateral knowledge exchange to develop mission-specific requirement sets during system specification; and by strengthening knowledge exchange relationships with scientists and engineers at Liverpool;
(ii) A range of National and International statutory nuclear and environmental regulators (e.g. UK NDA, Environment Agency (EA), Japanese Government (through ONDA's ISET-R project) will benefit potentially from the proposed detection methodology to refine and enhance processes and outcomes from emergency planning, routine monitoring (to comply with Environmental permits and statutory regulation) and long term monitoring or remediation; we will engage with these through our investigator and partner networks, including the Liverpool-led ARCoES network which has a strong portfolio of links with stakeholders in the nuclear environmental industry;
(iii) The commercial potential of the prototype Compton imager specification will be evaluated as part of the final reporting to identify any developing commercialisation pathways as they arise.


General Public
The subject of environmental radioactivity in the current climate of proposed nuclear installations and policy development is sensitive, and particularly with our partnership with potential end-users at Fukushima we will take great care to convey clear and coherent information to the public sphere, with the overarching aim of increasing public confidence and understanding of radioactivity in the environment. There is significant opportunity for the technology, objectives and outcomes of this proof-of-concept project to yield high profile stories about the application of UK science and technology in internationally-important environmental settings.

Educational opportunities and outreach
The investigator team has a network of international partners in and exchanges with Japan, the US and Taiwan in nuclear science and engineering which will generate lasting impact in strengthening academic-stakeholder networks around this developing technology. By developing educational experiences around the environmental applications of the Compton sensor technology (for example, 'towards the technology of the Star Trek tri-corder'), we will promote the science of environmental radiography to girls and boys at school level and the wider public, encouraging them into STEM education. The PDRA will be enrolled as a STEM Ambassador and British Science Association member and will take part in outreach and public appreciation of science activities both locally (e.g. Merseyside National Science and Engineering Week) and nationally (e.g., British Festival of Science).