The average person doesn't care about how much exposure nor do they want a physics lesson. I was in Kyiv Ukraine when the Chernobyl disaster took place and I can tell you a week before the news told us there was a disaster the information had made its way door to door (before Twitter, the Internet or texting). We heard of Iodine pills, red wine and the fact that kids can't take any exposure - hence all the children suffering from thyroid cancer in the years since ( I believe the official record is something like 4,000). When the Soviet government told us to stay inside, get rid of our clothes, cover our heads if we were going outside - it lasted for three days. You can't see radiation but you need food, you need to work and for many people they wanted to get out of the City. It was unbearably hot and with no air conditioning (which you couldn't use since you were supposed to keep your windows closed) you could choose to suffocate indoors or spend your last days enjoying the sunshine. By June there was no children left in the City of two million as everyone was frantic to get their children somewhere safe - thus for weeks you couldn't get anywhere close to the train, bus or air port to buy a ticket. You relied on your "social network" to help you out. I was lucky as I was Canadian and my student visa was done on June 19, 1986 so I flew home. The people in Japan are likely in the same state - hoping fate is on their side.