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Friday, Oct. 14, 2011

Fukushima said not Tokyo hot spot source

Radium-226 not used by nuclear reactors: expert


Staff writer

The high level of radiation detected in a Setagaya Ward, Tokyo, neighborhood fence that created a huge stir Thursday among the media and local residents probably was not fallout from the Fukushima No. 1 nuclear plant, the ward said.

News photo
Seeing is believing: Tsutomu Ozawa, a 72-year-old resident of Setagaya Ward, Tokyo, checks out a radioactive hot spot in his neighborhood Thursday. YOSHIAKI MIURA PHOTO

Setagaya Mayor Nobuto Hosaka told reporters that high levels of radiation were also detected around bottles stored underneath the floor of a house near the apparent hot spot — part of a home's wooden fence — and the ward is investigating their contents. At this stage, it remains unclear whether the two radiation finds are linked.

The Wednesday announcement about the high level of radiation in the fence in Setagaya was of grave concern to many residents in Tokyo. The chances of a highly contaminated hot spot being found at a site more than 200 km from the crippled Fukushima No. 1 plant had been considered unlikely.

Professor Masahiro Fukushi, a radiation specialist at Tokyo Metropolitan University who measured the fence's radiation level, told TV broadcaster Tokyo Broadcasting System Inc. it is highly probable the radioactive isotope detected is radium-226. As this isotope is not used in nuclear power plants, it is not believed to have been emitted by the Fukushima plant's wrecked reactors. Radium can be detected in some hot springs, Fukushi added.

The contamination is below the government level meriting an evacuation order, but the fence is located along a route children take to school, prompting Setagaya Ward to set up traffic cones and encourage kids to steer clear of it.

"This is an 'ultra-micro' hot spot and the (central) government could not detect it. Municipalities should really inspect radiation levels in detail and collaborate with citizens' groups like us," said Mizuho Nakayama, a member of Protect Kids from Radiation, which first detected the contamination and reported it to the ward on Oct. 3.

Setagaya Ward detected radiation of 2.707 microsieverts per hour at the fence, which is in the Tsurumaki district, on Oct. 6, and measured the radiation again twice Thursday. The day's preliminary reading was reportedly 3.35 microsieverts per hour.

News photo
Don't miss a spot: A worker checks the radiation level Thursday at a hot spot in Setagaya Ward, Tokyo. KYODO PHOTO

A level of 2.707 microsieverts per hour would be equivalent to 14.2 millisieverts per year, while 3.35 microsieverts per hour would be equivalent to 17.6 millisieverts per year, lower than the 20 millisieverts per year at which the government is supposed to order an evacuation.

It is widely believed that a one-time exposure to 100 millisieverts of radiation may increase the risk of dying from cancer by 0.5 percent.

The contamination appears to be limited to one site, as no other hot spots were found in Setagaya.

The ward measured radiation levels at 64 local elementary schools in the summer, and the highest reading was only 0.1 microsievert an hour.

"We received experts' opinions that there is nothing to worry about in terms of health even if you walk near (the fence). However, there are nursery schools and elementary schools in the vicinity and thus as a precaution, we put out traffic cones to prevent people from approaching the spot," the ward said in a press release.

The Wednesday announcement by Setagaya puzzled some experts. The wooden fence is apparently emitting the radiation, but radioactive materials usually build up on the ground. Radioactive materials that escape from a nuclear plant are tiny particles carried via wind and rain that eventually fall to the ground.

News photo

Fukushi of Tokyo Metropolitan University checked the site and tracked the radiation to a spot on the fence about 1 meter from the ground.

He said he checked the radiation a few centimeters above the ground and the level was less than 1.0 microsievert.

"It's very strange. Obviously it did not occur naturally. If it comes from rain, the ground should have high radiation. Trees nearby also have about a half or one-third of the radiation level, Fukushi said.

The ward office initially believed the relatively strong radiation came from the ground and scrubbed the walkway near the fence after Oct. 6, but the radiation level "barely dropped," said Setagaya official Ken Hatanaka.

"We are working with radiation experts to find out how to deal with the situation," he said.

"The ward should, of course, decontaminate the fence. But first, the ward should analyze what the substance is, where it comes from and why it is there," said Nakayama of Protect Kids from Radiation.

Kita Ward, Tokyo, detected radiation of 1.01 microsieverts per hour at the bottom of an elementary school downspout on Sept. 28, Kyodo News reported Thursday.

A relatively high level of radiation was also detected at several facilities in Karuizawa, Nagano Prefecture, with the highest reading — 1.7 microsieverts per hour — found at the bottom of an elementary school downspout. The town plans to decontaminate the hot spots.

False alarm in Funabashi

Staff report

Measurements by a citizens' group of high radiation at a park in Funabashi, Chiba Prefecture, proved to be incorrect, the city said Thursday.

The group reported readings of 5.82, 2.1 and 1.79 microsieverts per hour at three locations in Anderson Park, but the city measured 0.91, 1.40 and 0.79 microsierverts per hour at the same spots Thursday.



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