This app displays radiation measurement data for Japan before and after 03/2011.
On Friday, March 11, 2011, an earthquake followed by a tsunami devastated the Tōhoku region of Japan. On that same day, a nuclear meltdown occurred at the Fukushima Daiichi Nuclear Power Plant.
http://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami
This app contains radiation measurement data for March 2011, so you will be able to see the radiation levels in Japan before and after March 11. The data comes from the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT).
Blog: http://tinyurl.com/radiation-map-japan
Download