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Scientists Find Radiation Detection Methods Lacking By David Francis WASHINGTON — Radiation monitors used by the Homeland Security Department would probably be unable to detect small quantities of highly enriched uranium coming into the United States, according to a letter sent to two U.S. lawmakers last week by the American Association for the Advancement of Science (see GSN, June 8). The organization’s Center for Science, Technology and Security Policy asked physicists Frank von Hippel of Princeton University and Steve Fetter of the University of Maryland to review port radiation monitoring methods. Their findings were reported in a letter from association Director Norman Neureiter to Representatives Edward Markey (D-Mass.) and Bennie Thompson (D-Miss.), who had asked the association to explore the matter. The House Homeland Security Committee plans to explore the effectiveness of detection methods at U.S. ports at a hearing this afternoon. In the letter, Neureiter cautioned that the findings were limited to unclassified information about the monitors. However, based on the available information the association confirmed the findings of an earlier report, which concluded that small amounts of highly enriched uranium would go undetected by U.S. monitors. “Relatively simple means exist for avoiding detection that could allow kilogram quantities of HEU to evade detection by even significantly more sensitive and sophisticated passive detection systems than those presently in use,” Neureiter wrote. The monitors are constrained by poor energy resolution, which hinders their ability to differentiate between radioactive materials and normal cargo. The large distance from the monitor and the cargo being inspected, the short time that the monitor scans the cargo and background signals also limit monitors’ effectiveness, wrote Neureiter. He recommended additional research and development to combat these flaws. Neureiter warned that existing monitoring technology would not be likely to identify highly enriched uranium already in a nuclear weapon. “We note that any system that depends on detecting HEU at a U.S. port of entry is a source of great danger if that HEU has been fashioned into a nuclear device,” Neureiter wrote. “Such a device could easily be set to detonate automatically upon arrival at a U.S.” port. Neureiter backed a proposal to develop an “offshore detection integrated system” for cargo heading to the United States. Under this proposal, monitors would be secured to cargo containers at the port of origin, allowing for collection of data while the cargo in en route. Finally, Neureiter recommended active HEU detection, using such methods as radiography or fission stimulation with neutron sources. Methods being developed by at Oak Ridge and Lawrence Livermore national laboratories might prove effective, Neureiter said. The unreliability of detection methods mandate that highly enriched uranium must be secured against diversion, Neureiter wrote. The material “should be accorded the same level of security as nuclear weapons. Efforts also should be made to reduce and eliminate stocks of HEU whenever possible,” the letter states. “The conversion of HEU-fueled research reactors and critical assemblies, which are still widespread, is also very important” (see GSN, May 26). In the short term, Neureiter suggested taking more time to examine cargo and narrowing the width of monitors. New shields could be added to decrease background radiation, he said. The report confirms suspected inadequacies in the U.S. nuclear detection system, Markey said. “This report reveals what we have suspected to be true. The system in place for detecting nuclear materials at our ports will not effectively detect highly enriched uranium … from being smuggled into the United States,” he said in a press release. “The Bush administration finally needs to confront the reality that the laws of physics are working against them in their quest to stop highly enriched uranium at our borders.” “While there are some short-term engineering fixes and some longer-term R&D that can help make these detection systems better the reality is that the only sure-fire way to prevent a terrorist from smuggling nuclear weapons-grade HEU into this country is to spend more time and money securing it before it reaches our shores,” Markey added.
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