During the last several weeks, radiation has been carried west by prevailing autumn wind patterns, resulting in an increase in radiation in the northern parts of Gunma prefecture and some limited areas of Chiba.
For the first time in several months, on Oct. 6 air-borne radiation levels were in the 10,000 *becquerel range in the extreme northwest corner of rural Tokyo, far away from the metropolitan area.
However torrential overnight rains have probably dispersed clouds carrying radioactive particles resulting in generally lower levels of air-borne radioactivity throughout the Kanto region, according to MEXT.
In the aftermath of the 1986 nuclear accident in Chernobyl, areas where radioactivity levels exceeded 37,000 becquerels were designated as contamination zones, noted the Asahi newspaper.
*The difference between becquerels and sieverts is that becquerels measures radiation emitted and sieverts measures potential for damage to the human body. This is only one of many differences.