Fukushima ‘hot spots’ raise
radiation fears But experts see little threat from patches
of heightened radioactivity. Geoff Brumfiel The discovery of ‘hot
spots’ of radioactive
material is spreading
fear far beyond the
damaged Japanese
nuclear power plant at Fukushima. But experts
say that there is no
threat from the small
spots of increased
radioactivity now being
discovered in large-scale surveys. On 12 October, officials
reported finding 195
becquerels of
strontium-90 on a
rooftop in Yokohama, some 250 kilometres
south from the Fukushima Daiichi plant. A day later, a citizen’s group in Funabashi,
Chiba Prefecture, about the same distance
away, made radiation readings of 5.82 microsieverts per hour (μSv h –1) at a children’s theme park. The same day, an
inspection of Tokyo’s Setagaya district
turned up a narrow strip of pavement that seemed contaminated, at 3.35 μSv h–1. Officials later traced the Tokyo
contamination to an abandoned house
containing bottles of radium-226, a
radioactive element once used in luminous
paint. Counting the risk Since the Fukushima accident, the Japanese
government’s official safety limit for
radiation exposure is 20 mSv per year,
which corresponds roughly to a rate of 2.28 μSv h–1. Yet the newly discovered hot spots pose no threat to human health, says
Geraldine Thomas, a radiation-health expert
at Imperial College in London. Total radiation
dose is measured by the strength of the
radioactivity in a given area and the
amount of time a person spends there. The small sizes of the hot spots make it all but
inconceivable that anyone would receive 20
mSv, she says. Strontium-90 can cause bone
cancer if ingested, but a small patch on a
roof won’t cause that problem, Thomas
says. “These are minuscule amounts of radiation, but the population out there is
terribly nervous.” Risk is about more than radiation readings,
adds Christopher Clement, the scientific
secretary of the International Commission
on Radiation Protection in Ottawa, Canada,
an independent international organization
that provides guidance on safe levels of radiation. Its ‘recommended’ residual dose
from a nuclear accident is between 20 and
100 mSv per year for the general
population. The Japanese government has
chosen the lower number as its official limit,
Clement says, but “it’s not a magical number by any means”. Clement says that most
scientists believe that receiving an
additional 100 mSv of radiation over a
prolonged period can raise the chance of
dying of cancer by 0.5% (in the general
population the chance of cancer being the cause of death is about 25%). Under the limit To reach that 100-
mSv dose would
require someone to
be continuously
exposed to the
Japanese government’s 20-
mSv limit for 24
hours a day, seven
days a week over a
five-year period. A
small amount of radioactive material
on a rooftop or in a gutter poses little risk.
“People don’t sleep in that one spot in the
gutter,” he says. Both Clement and Thomas say that more hot
spots are likely to be discovered as citizens’
groups, local authorities and government
inspectors continue their surveys. And
Clement says that everyone should be
prepared for more false alarms like the one in Tokyo: “No matter where you go in the
world, if you take a radiation instrument
with you and look around, you’ll eventually
stumble across something that’s above
what the background for that area normally
is,” he says.

Author: renjiveda

I'm not I

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