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Saturday, Oct. 15, 2011

Tokyo radiation scare turns out to be radium stored under house floor

Staff writer

Dozens of bottles and test tubes emitting high radiation levels that were found Thursday in a house in Setagaya Ward, Tokyo, contained a white powdery substance believed to be radium-226, which can be used as luminous paint, the science ministry said Friday.

Some of the bottles and test tubes were labeled "Nihon Yako," which could be the name of a luminous paint company, according to the ministry. "Yako" means luminous.

The bottles were removed from the premises Friday afternoon and will be stored by a radioactive isotope disposal agency, the ministry said.

Despite the initial fear in the neighborhood that the high radiation levels were coming from radioactive materials emitted by the Fukushima No. 1 nuclear plant, the bottles and test tubes had been sitting underneath the floor boards of the vacant house in the Tsurumaki district, the ministry said.

A radiation level of 600 microsieverts per hour was measured around the surfaces of the bottles, which had been contained in a wooden box.

At 1 meter from the bottles, the reading was 20 microsieverts per hour, science ministry official Takao Nakaya said.

After the ministry officials locked the bottles and tubes into a lead container, the radiation level declined to between 0.1 and 0.35 microsievert per hour, he said.

The owner of the house, a woman who is reportedly around 90 years old, said she had never seen the bottles before and had no idea why they had been stored under the floor, according to the science ministry.

The woman's deceased husband was an office worker and had nothing to do with radioactive isotopes, the ministry said. The woman lived in the house from around 1953 to February this year but now lives elsewhere.

She lived alone in the house since after her husband died a decade ago. According to the ministry, the owner's daughter has been checking the home now and then for the past few months.

Although the ministry estimated that the woman may have been exposed to about 30 millisieverts per year, no ill effects from radiation have been confirmed. The calculation was made based on an estimate that the woman had slept in a bed about 2 meters from the bottles. Experts say that if a person is exposed to 100 millisieverts of radiation, the risk of dying from cancer increases by 0.5 percent.

Radium-226, which in the past was used as luminous paint, has an extremely long half-life — 1,600 years — and emits gamma, alpha and beta rays, said Masahiro Fukushi, a professor of radiation at Tokyo Metropolitan University.

Although alpha rays and beta rays can be blocked by a paper or metallic plate, gamma rays are very powerful and penetrate most materials.

When radioactive radium is ingested or inhaled, it accumulates in bones, and thus can lead to cancer, Fukushi said.

In Japan, the radiation hazard prevention act stipulates that a person or an organization must register with the government when storing substances that contain 10 becquerels per gram of radioactive materials and when the total amount exceeds 10,000 becquerels.

However, unregistered radioactive materials are found at an average of about once a year, mostly in shuttered hospitals or abandoned offices, according to Nakaya of the science ministry.

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The Japan Times

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