Although experts debate the ease of building a crude nuclear bomb, no one disputes that it is far easier to build a simpler weapon known as a dirty bomb—a conventional bomb that scatters radioactive material. A dirty bomb produces no nuclear chain reaction, no mushroom cloud. Yet its aftereffects could be devastating. In a 2002 computer simulation run by the Federation of American Scientists, a single foot-long piece of radioactive cobalt of the type commonly used in food-irradiation plants was blown up with TNT in lower Manhattan.