Air dose levels in an 80-kilometer area surrounding the crippled Fukushima No. 1 nuclear power plant have dropped by 47 percent since November 2011.
The latest readings for September were announced on Dec. 25 by the Nuclear Regulation Authority, the government’s nuclear watchdog.
“Two and a half years after the accident, radiation levels have steadily decreased,” an NRA official said.
NRA officials attributed the drop primarily to natural decay. They said rainwater has also washed some of the radioactive materials into the ocean and some into the surrounding soil.
The air dose rates 1 meter above ground are estimated from airborne radiation levels measured by aircraft. Comparable figures have been available since November 2011, seven months after the Great East Japan Earthquake and tsunami triggered the Fukushima nuclear accident.
Readings in November 2012 showed a 40 percent decrease from November 2011.
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