Suffice it to say, the further the better. To gain a further understanding how a nuclear blast can spread radiation, you can plot a detonation from the Blast Mapper in three simple steps. Here are a couple of sample blows for two random cities. The plots on the left indicate the range of fallout and the two on the right indicate what type of damage would be sustained from a one megaton bomb. Since the 25 megaton blast is so massive and less likely, these were not plotted though you can do so on the Blast Mapper site.
Death can occur within hours of exposure.
About 10 years will need to pass before levels of radioactivity in this area drop low enough to be considered safe, by U.S. peacetime standards. Death occurs in 2 - 14 days. 160 miles Causes extensive internal damage, including harm to nerve cells and cells that line the digestive tract. Also results in a loss of white blood cells and temporary hair loss. Two to three years will need to pass before radioactivity levels in this area drop low enough to be considered safe, by U.S. peacetime standards.