Imaging and Detection of Radioactive Material - Portable Gamma Ray Imaging Spectrometer (PGRIS)

Terrorist threats to the UK take many forms, often abbreviated to CBRNE (Chemical, Biological, Radiological, Nuclear and Explosive). This project will produce a prototype of an advanced type of hand-held radiation detector capable of imaging and accurate spectroscopy, which is relevant to the last three of these areas. Our device can identify precisely and locate radioactive materials that emit gamma rays. Our portable gamma-ray imaging spectrometer will be used to track down and characterise the radiation which has triggered a general purpose portal scanner. The radiological threat comes from what are sometimes called "dirty bombs" or more generally from any method used to release radioactive material in such a way as to cause a threat to the general public. In order to deal with the radiological threat it is necessary to be able to locate and identify radioactive materials quickly. In addition, in the event that a dirty bomb is exploded, it is vital to be able to monitor the effects by establishing what radiation was emitted and its location. The nuclear threat comes from nuclear weapons proliferation and in this case the need is to detect special nuclear materials (Uranium and Plutonium). Our device will be able to detect and locate the weak gamma rays emitted by these materials. Explosives cannot be detected directly by a radiation detector because they normally do not emit gamma rays. However, if they are bombarded by neutrons then they will be activated and will emit characteristic gamma rays, which enable them to be detected and identified. The same technique can be used to search for illegal drugs. There are already portable radiation detectors, but generally these use scintillators to detect gamma radiation and so the energy resolution is limited which means that gamma rays that are close in energy cannot be distinguished from each other. An alternative is to use Germanium for the detector element. In this case the resolution is very good, but the detector is very expensive and Germanium only operates well as a detector when it is cooled to temperatures around -200C. Our detector uses a semiconductor called Cadmium Zinc Telluride (CZT) which works well as a detector at room temperature. It has much better energy resolution that scintillators and is nearly as good as Germanium. There are a few other portable detectors using CZT detectors, but none which combine this good spectroscopic resolution (for identifying materials by their characteristic gamma-ray energy) with imaging capability to locate the sources of the radioactivity.