Radiation in Tokyo not linked
Japanese Nuclear Meltdown
EMF Radiation Protection
Magnetic Field Meters
14 October 2011
Radiation level on Tokyo street was 17 times recommended
limit but came from radium kept under house floorboards
Concerns that contamination from the Fukushima Daiichi plant
had spread to Tokyo subsided on Friday after high levels of
radiation recorded along a street in the city were linked to
old bottles of radium stored beneath the floorboards of a
Researchers had recorded radiation of 3.35 microsieverts per
hour along a street in Setagaya ward, a higher level than in
some parts of the 12-mile (20km) exclusion zone around the
An investigation traced the contamination to several bottles
that had been stored in a cardboard box beneath an empty
house. The bottles recorded radiation levels in excess of
those measurable on a low-dose radiation counter, said
Setegaya's mayor, Nobuto Hosaka.
Science ministry officials believed the bottles contained
radium-226, a radioactive material used in fluorescent paint
on watch faces and in medical devices, the Yomiuri Shimbun
said. Radiation levels inside the house dropped
significantly after the bottles were placed inside a lead
container, reports said.
The hourly reading in the Setagaya hotspot, located close to
a nursery school, was equivalent to 17.6 millisieverts (mSv)
a year, according to science ministry calculations, just
below the 20mSv a year required to trigger an evacuation and
more than 17 times the internationally recommended level for
the general public.
Officials said the area had been cordoned off, adding that
the contamination levels did not pose a threat to health.
The reading in Tokyo was taken a metre above the ground near
a hedge, according to the public broadcaster NHK. Other
spots along the same street showed lower readings.
Although this recent incident is not connected to the
Fukushima disaster, the discovery comes amid concern that
fallout from the plant may have spread over a much wider
area than previously thought.
Kyodo News reported that a citizens' group detected levels
as high as 5.82 microsieverts an hour in a park in the town
of Funabashi, Chiba prefecture, 130 miles from Fukushima.
That is five times higher than the highest levels recorded
in the city since the 11 March disaster.
Earlier this week officials in Yokohama, just south of
Tokyo, said they had found abnormally high levels of
strontium-90 in sediment on the roof of a block of flats.
The radioactive isotope, which has a half-life of 29 years,
can accumulate in the bones and cause bone cancer and
leukaemia. In September officials in Yokohama said they had
detected 40,200 becquerels of radioactive caesium per
kilogramme of sediment collected from a roadside ditch.
The task of identifying how far the contamination has
spread, and in what quantities, is proving difficult. Wind
direction and topology can cause radiation to spread
unevenly, and particles are more likely to gather in ditches
and other places that accumulate dust and rainwater.
Setagaya ward officials said they would screen more than 250
other locations in the area over the next month. Radiation
levels in the neighbourhood, which has a population of more
than 840,000, have not dropped despite decontamination
Children have been warned to avoid the recently discovered
hotspot, now blocked off by several plastic cones, on their
way to and from school.
"I thought the reading must have been a mistake when I first
saw it," Hosaka told the broadcaster TBS on Thursday. "Once
we have confirmed the readings as high we will push ahead
with decontamination efforts."