A radiation hotspot has been detected in Tokyo, reports said Thursday as researchers carry out stringent tests to map how far contamination has spread from the crippled Fukushima nuclear plant.
Japanese media said researchers found radiation levels of 3.35 microsieverts per hour along a street in the west of the capital -- 220 kilometres (136 miles from Fukushima -- much higher than previously reported levels.
According to calculations based on the Japanese science ministrya's criteria, the equivalent annual dose in the hotspot would be 17.6 millisieverts, just below the 20 millisieverts per year threshold that requires evacuation.
The reading is also higher than levels measured recently at Iitate, an area in Fukushima prefecture that has been evacuated.
The reading in Setagaya was taken one metre above the ground near a hedge, national broadcaster NHK said, while other parts of the same sidewalk showed lower readings.
The reading came after ward authorities said Wednesday that levels of 2.7 microsieverts per hour had been detected on October 6, higher than levels of less than 0.1 microsieverts in other parts of Setagaya according to official data.
The higher readings come as more tests illustrate how far fall-out from the Fukushima disaster have spread, with elevated levels of radioactive caesium recently found as far away as Yokohama, more than 241 kilometres (150 miles) from the plant.
Radiation fears are a daily fact of life in many parts of Japan following the earthquake and tsunami-sparked meltdowns at the plant, with reported cases of contaminated water, beef, vegetables, tea and seafood.
Variable winds, weather and topography result in an uneven spread of contamination, experts say, and radioactive elements tend to concentrate in places where dust and rain water accumulate such as drains and ditches.
Setagaya ward did not immediately confirm Thursday's reading. "We don't know the cause (of the high radiation levels) yet. We are asking experts to find it urgently and decontaminate the area," a spokeswoman said.
She added that the high readings have been shown only in a two-metre long area and below 1.5 metres from the ground.
"We also plan to check sand in the ward's 258 parks over one month from late October," she told AFP.
Radiation levels in the area have not fallen since the ward's efforts to decontaminate it on October 6, and authorities are instructing children to avoid the walkway as they go to school.
Setagaya Mayor Nobuto Hosaka told TBS: "I thought the reading must be a mistake when I first heard. We will push ahead with decontamination after confirming levels are high."
The March 11 earthquake triggered a tsunami that tore into Japan's northeast coast, leaving 20,000 people dead or missing, while sparking meltdowns and explosions at the Fukushima Daiichi nuclear power plant.
The subsequent release of radiation forced the evacuation of tens of thousands from a 20 kilometre (12 mile) radius from the plant and spots beyond in the world's worst nuclear accident since the Chernobyl disaster in 1986.
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