Bloomberg News

Radium, not Fukushima, Source of Western Tokyo Radiation Spike

October 14, 2011

Oct. 14 (Bloomberg) -- Radioactive radium-226 was the source of a high radiation reading in Tokyo’s Setagaya district yesterday, officials said, ruling out the possibility it may have come from the crippled Fukushima nuclear reactors.

An investigation of a house near the contaminated area turned up two boxes of bottles containing radium-226, Takao Nakaya, head of the Science Ministry’s office of the radiation regulation, said by phone today.

“The high readings have nothing to do with Fukushima,” Nakaya said.

Investigators found the radium under the floor of the house in Tsurumaki 5-chome and readings suggested an elderly woman who had been living there until February may have been exposed to radiation 30-times safety levels, Nakaya said. The ministry is investigating where the radium came from, according to another ministry official Tomokazu Ueda.

The woman is about 90 and her daughter told officials yesterday she had no knowledge of how the radium got under the floorboards, said Nakaya. The elderly woman has an illness unrelated to radiation and he declined to give more details citing privacy laws.

Radium-226, which has a half-life of about 1600 years, is a naturally-occuring radioactive metal and has uses in x-rays and luminiscent paint, according to the U.S. Environmental Protection Agency. Long term exposure to radium increases the risk of cancer, the agency said.

Setagaya ward, a mostly residential district with a population of more than 840,000 people, is 233 kilometers (145 miles) from the Fukushima reactors leaking radiation.

Other Areas

Other areas in Tokyo and Yokohama have reported radiation readings requiring further investigation, with most originating from local residents using personal dosimeters.

Setagaya adjoins Ota ward where radiation levels exceeding the ward’s own safety standard of 0.25 microsieverts per hour were detected at 13 schools, according to the Ota ward board of education.

In Yokohama, officials are testing samples in an area of Kohoku ward after a resident removed sediment from an apartment building roof that laboratory tests showed contained strontium found in radioactive fallout.

“We received data from a resident about strontium and we are carrying out an investigation in the neighborhood by picking up samples for lab tests,” said Yokohama city official John Kuramochi yesterday. He declined to confirm if the first lab tests showed the sediment contained strontium 90.

Strontium 90 has a similar structure to calcium and tends to accumulate in bone and can cause bone cancer and leukemia, Hiroaki Koide, a nuclear physics scientist at Kyoto University, said yesterday by phone.

--Editors: Peter Langan, Aaron Sheldrick

To contact the reporters on this story: Chisaki Watanabe in Tokyo at;

To contact the editor responsible for this story: Peter Langan at

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