The Defense Threat Reduction Agency has chosen three contractors to build up to four test beds at U.S. military sites that will be used to develop and field systems that can detect and defeat unconventional nuclear weapons, such as dirty bombs. DTRA is pursuing the project along with the National Nuclear Security Administration. On Monday (April 15), DTRA selected Washington Group International, Inc., TRW Systems and Applied Research Associates, Inc. to start work on the test beds, two of which...