A radiation detector indicates 0.6 microsieverts, on March 15, 2011, near Shibuya train station in Tokyo, four days after a strong earthquake damaged a nuclear power plant in Fukushima Prefecture, northeastern Japan.
PICTURES: Devastation in Japan
PICTURES: Tsunami reactions around the world
PICTURES: Search and rescue in Japan
PICTURES: World's biggest tsunamis
PICTURES: How earthquakes are measured
PICTURES: Deadliest earthquakes
PICTURES: Quake, tsunami slam Japan
Credit: AP Photo/Kyodo News