Airborne radiation near Fukushima nuclear plant below physical half-life of cesium

10 September 2015

Airborne radiation dosage at 1 meter above ground level in evacuated areas within a 5-kilometer radius from the crippled Fukushima Daiichi nuclear power plant is decreasing at a rate faster than the physical half-life of radioactive cesium, according to a Japan Atomic Energy Agency (JAEA) research team report at the Atomic Energy Society of Japan’s autumn meeting in Shizuoka on Sept. 9. The report cited findings from a JAEA survey of radiation in the air conducted by unmanned helicopters in response to the nuclear accident at the Fukushima Daiichi plant of Tokyo Electric Power Co.

“This data supports the fact that there has been no further spewing of highly radioactive substances from Fukushima Daiichi,” said Mitsuo Imura, a member of the JAEA Fukushima Environmental Safety Center who presented the results.

On the other hand, if studied in combination with research results by another researcher who looked into soil content within the 5-km radius from the plant, the fact that radioactive cesium on the ground surface gradually seeps underground over time can also be a reason for the decrease in airborne levels, Imura said.

The survey was conducted on six occasions between August 2012 and March 2015. If the first measurement of airborne radiation dosage in October 2014 is assumed as the standard of 100%, the latest survey amount represents a decrease to 55% as of January 2015, according to the team. This was 10 percentage points lower than the previously predicted level.

(Translated by Kyodo News)