The elevated radiation levels discovered in Tokyo's Setagaya Ward have been confirmed—thankfully—as not having originated from the damaged Fukushima power plant. So what was causing the Geigers to jump? A stash of radium-226 under a home's floorboards.
The mystery, though, is how they got there.
Japan's Science Ministry discovered the cache Thursday which consisted of numerous bottles and vials containing a white, powdered substance believed to be radium. Some containers bore the label, Nihon Yako ("Luminous Japan")— radium-226 can be used as a luminous paint.
Radiation levels at the surface of the bottles measured 600 microsieverts per hour. The elderly owner of the home said she was unaware of the materials stored beneath her. She reportedly had lived in the home from 1953 until February of this year while receiving about 30 mSv of exposure annually. Radium, when inhaled or ingested, accumulates in the bones and for every 100 mSv of exposure, increases one's chances of dying from cancer by one half percent.
Authorities have removed the isotopes from the property and stored them at a radioactive isotope disposal agency for the duration of their 1,600-year half life. [Japan Times]