This is a graph of the spread of RADS (which is
"unit of energy absorbed from ionizing radiation, equal to 100 ergs per gram or 0.01 joules per kilogram of irradiated material." according to Princeton) from the Fukushima Daiichi Plant from the Australian Radiator Services. A huge number of RADS can travel from Japan, all the way to the U.S. in a matter of 6 to 10 days.
Japan brought in other countries and experts to maintain transparency with the public about what was happening at the plants after the earthquake and the tsunami. This site is a wealth of information on energy
The US EPA (Environmental Protection Agency of America" suggest simple things to do to avoid radiation exposure such as wearing heavy clothes and making a shield to protect your skin from the radiation.