|Radiation monitoring||- Radiation Monitoring|
By: David Hambling
Date: March 07, 2008
Spotting smuggled nuclear and radiological materials won't be easy, a report from the Royal Society says. One thing that could help: robotic aircraft.
The report gives the findings of a workshop which brought together seventy experts from the U.K., U.S., Russia, Israel and Europe to look at the technical aspects of locating smuggled radioactive elements. They concluded that there is not likely to be magic solution to the problem, and highlighted the vital need for greater international co-operation. The report did make some interesting points about the technology of detectors, however.
In the near term (3-5 years) low cost detectors with improved energy resolution for gamma ray spectroscopy will remain the key priority. Germanium based detector technologies remain the gold standard and developments in cooling will improve and broaden their field applications. In the medium term (5-10 years), there are promising opportunities to develop new technologies, such as muon detection systems. In the long term (10-20 years) detection could benefit from advances in nanotechnology and organic semiconductors.
The report also describes the possibilities for using small unmanned aerial vehicles, or UAVs, to hunt for these dangerous material -- especially in urban areas
Aerial detection platforms include fixed wing aircraft, helicopters and unmanned aerial vehicles and detection systems tend to use externally mounted high resolution scintillation detectors to exploit a larger field of view. This increases the area survey rate so that more readings can be taken of a larger area in a given time. As the distance between the detector and the source increases, radiation flux is attenuated in air and scattered radiation builds up. This eventually limits the effective working distance from which a given source can be detected.
High energy gamma radiation, above a few hundred keV, can be observed up to a distance of approximately 100m above ground. Lower energy radiation limits the potential for airborne observations to altitudes of 30m. SNM [smuggled nuclear material] could be detected from the air in open spaces through the radioactive signatures of uranium-235 (235U) and the plutonium decay product, americium-241 (241Am). These emit low energy gamma rays and require operational altitudes as low as 10-30 m.
The report notes that Israelis are already experimenting with this capability and have an experimental craft kitted for radiation detection.
The Israeli Caspar UAV prototype can fly at a height of up 700 m at speeds of 20-85 km/h for up to 1.5 hours, and its field of view is over 10 km. The Caspar includes an off-the-shelf, combined gamma and neutron CsI(TI) (caesium iodide doped with thalium iodide) radiation detector, in addition to a camera and a global positioning system (GPS).
It can fly at low altitude and transmit both its detection data and position in real time to a ground based team. Advantages of UAV systems are that they are light weight and can be deployed rapidly from any site. They are also considerably less costly to operate than aircraft and helicopter based systems. Being unpiloted and remote-controlled, they minimise radiation exposure to personnel and can even be disposed of afterwards if contaminated. These features make UAVs ideal for fast scanning and mapping of large contaminated areas, and monitoring and sampling radioactive plumes.
Read the full report on "Detecting nuclear and radiological materials" here.
With the potential commissioning of new nuclear reactors throughout the world, to offset the increasing energy demands and need to manage pollution levels, the ability to monitor radiation levels in the vicinity of such reactors assumes a growing importance. This example from Yamaha Motor Corporation concerns the Japan Nuclear Cycle Development Institute Wakasa Wan Energy Research Center- from 2000.