The amount of nuclear material recorded as missing from licensed sites around the world suggests smuggling is rife, but inadequate equipment at national borders means seizures by customs are few and far between (New Scientist, 26 May 2001, p 10).
US borders are patrolled by officers wearing "pagers" that detect the high levels of gamma radiation emitted by nuclear material. Some sites also have drive-through radiation detectors for checking cargo containers. But if the material being smuggled is shielded with a dense metal like lead, neither of these systems will detect it.
To crack down on nuclear smuggling, scientists at the Idaho National Engineering and Environmental Laboratory (INEEL) in Idaho Falls and the Lawrence Livermore National Laboratory in Los Alamos, New Mexico, set about making a new detector with ARACOR, an imaging company based in Sunnyvale, California.
The system they developed produces high-energy X-rays that can penetrate cargo containers and common shielding materials. If the X-rays hit uranium or plutonium they induce fission reactions, splitting their nuclei into smaller fragments. In the process, neutrons are emitted that can pass through shielding materials and be picked up by a neutron detector outside.
A $3.5 million prototype system is being tested and is likely to go into widespread use within the year, says James Jones, the physicist in charge of the project at INEEL. "We're monitoring the effort," says John Penella, a nuclear expert at the US Customs Service. "If it proves technically feasible, we'll install it."
The system isn't foolproof though, warns Thomas Cochran of the Natural Resources Defense Council, a pressure group based in Washington DC. He says materials with a high hydrogen content, like some plastics, can effectively shield neutrons. Instead of pouring money into detecting nuclear material as it crosses national borders, more should be spent on securing research labs where nuclear material is being stolen, he says.
Nicola Jones l
New Scientist issue: 11 January 2003
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