Citing threat of ‘dirty bombs,’ GAO report says U.S. fails to protect against theft. The United States is failing to prevent terrorists around the world from stealing radioactive materials that could be used to make explosives known as “dirty bombs,” according to a blistering congressional report obtained by NBC News. THE REPORT, issued by the General Accounting Office, the investigative arm of Congress, said 612 “sources of radioactive materials” had been reported stolen worldwide in the last eight years. So far, 254 of those sources still had not been recovered, it said. Low-grade radioactive materials used in medicine and industry are considered good sources for radiological dispersal devices, popularly known as “dirty bombs,” which are generally low-grade radioactive materials enfolded in ordinary explosives. The devices are not nuclear weapons, but they spew their radioactive payloads over the area of the blast and are considered especially effective weapons of terror. Full Story