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Radiation risksHighly concentrated radiation found in Tokyo

Published 17 October 2011

A recent study indicates that radiation from the Fukushima Daiichi nuclear power plant, which suffered a meltdown following the 11 March earthquake and tsunami in Japan, has spread further and was more concentrated than previously thought

A recent study indicates that radiation from the Fukushima Daiichi nuclear power plant, which suffered a meltdown following the 11 March earthquake and tsunami in Japan, has spread further and was more concentrated than previously thought.

A thorough investigation by Japanese researchers found high levels of radioactive material in concentrated areas in Tokyo and Yokohama, more than 150 miles away from the Fukushima Daiichi nuclear plant.

In Tokyo, one sidewalk in the western part of the city had recorded radiation levels of 2.707 microsieverts per hour, roughly fifty times higher than any other location in the ward where the high levels were detected.

What’s puzzling is that the levels detected on other parts of the same sidewalk were very low,” said Ken Hatanaka, head of the ward’s section in charge of radiation monitoring.

Hatanka added that the local authorities are working with experts to determine how to decontaminate the highly radioactive spot.

Meanwhile, in Yokohama local officials say last month they detected 40,200 becquerels of radioactive cesium per kilogram in sediment collected from a roadside ditch.

The Japanese government has banned the use of rice fields that have been found with more than 5,000 becquerels of cesium per kilogram of soil.

Rainwater and sediment containing radioactive materials may have built-up in such spots resulting in the higher readings, but officials say these contaminated areas do not pose any immediate danger to residents living nearby as radiation levels remain very low, even in sites near the newly discovered contamination sites.

In the same ditch where 40,200 becquerels were detected, another spot recorded only 3,030 becquerels. In addition airborne radiation levels near these spots was low.

We’ve always known that there are ‘hot spots’ where contamination levels are higher than other areas, but these tiny spots are like ‘micro hot spots’,” explained John Kuramochi, who leads Yokohama’s radiation monitoring division.

According to Akira Hanawa, the head of the Isotope Research Institute in Yokohama, radioactive contamination spreads unevenly depending on the wind, weather, and topography. Furthermore, “radioactive elements later accumulate in specific spots that tend to gather dust and rain water, such as ditches,” Hanawa said.

The most recent discoveries come as Japanese researchers, local governments, and residents are stepping up their monitoring of radiation.