The “dirty bomb” allegedly planned by terror suspect Jose Padilla would have been a dud, not the radiological threat portrayed last week by federal authorities, scientists say. At a June 1 news conference, the Justice Department said the alleged al-Qaida associate hoped to attack Americans by detonating “uranium wrapped with explosives” in order to spread radioactivity. But uranium’s extremely low radioactivity is harmless compared with high-radiation materials — such as cesium and cobalt isotopes used in medicine and industry that experts see as potential dirty bomb fuels. Full Story