An irradiator, a large, cabinet-like piece of equipment, can instantly kill millions of infectious microbes in meat and other foods, the job being done by cesium chloride powder or another radioactive material packed inside. But those powerful isotopes could also be used by a terrorist making a “dirty bomb.” Should such irradiators be banned? “It’s a question of costs and benefits,” said Mohamed ElBaradei, head of the U.N. nuclear agency. “We’d like to maximize the benefit and minimize the risk.” The question is one of many being pondered by participants at the first high-level global conference on the threat of radiological dispersal devices, also known as dirty bombs, a three-day meeting that got under way Tuesday beneath the soaring frescoed ceilings of an old Hapsburg palace. Some 600 scientists, law enforcement officials and others, an overflow crowd, filled a vast rococo ballroom to discuss something that hasn’t even materialized yet. ElBaradei cautioned reporters, however, “The fact that you haven’t seen one doesn’t mean one isn’t imminent.” Full Story