It begins with a flash brighter than the sun. Trees, fences, and people immediately catch fire. The only reason you survive is because you run inside and dive into the cast-iron tub just as the shock wave arrives. You stumble to your lopsided front door and look out on the burning ruin of your neighborhood. The deadly radioactive fallout is on its way. Should you stay in your wobbling house or run across town to the public library to shelter in its basement? A new mathematical model may have the answer.
The model is the brainchild of Michael Dillon, an atmospheric scientist at Lawrence Livermore National Laboratory in California. He started exploring the topic about 5 years ago after the U.S. government called for more research on nuclear shelters. Curious about his work, his family asked him what they should do if they saw a mushroom cloud. "I realized that I really didn't have a great answer," he says. The official U.S. government advice is to "take shelter in the nearest and most protective building." For most people, that would be the basement of their home. But, Dillon says, "out in California there just are not that many basements," offering little protection from fallout. For those people, the official recommendations suggest "early transit" to find better shelter, ideally one with thick layers of concrete over your head and plenty of food and water. But if you spend too much time outside in the fallout, you're toast.
During the Cold War, scientists modeled almost every imaginable consequence of a nuclear explosion. But Dillon found a gap in the sheltering strategies for people far enough from ground zero to survive the initial blast but close enough to face deadly fallout. He focused on a single low-yield nuclear detonation like those that destroyed Hiroshima and Nagasaki. The world's nuclear arsenal has grown far more powerful - today's warheads can inflict thousands of times more damage - but security experts believe that low-yield bombs are the kind most likely to be used by terrorists.