Concerns are growing that Al Qaeda or a related group could detonate a “dirty bomb” that would spew radioactive fallout across an American or European city, according to intelligence analysts, diplomats and independent nuclear experts. Although safeguards protecting nuclear weapons and their components have improved, experts said the radioactive materials that wrap around conventional explosives to create a contaminating bomb remained available worldwide — and were often stored in non-secure locations. Detonating a dirty bomb would not cause the death and devastation wrought by a nuclear weapon, but officials and counter-terrorism experts predicted that it would result in some fatalities, radiation sickness, mass panic and enormous economic damage. Intelligence agencies have reported no reliable, specific threats involving dirty bombs or nuclear weapons, but senior U.S. and European officials and outside experts said several factors had heightened fears in recent weeks. Full Story