The peak of radiation emitted from the Fukushima Dai-ichi nuclear power plant reactors, which rained down on the Kanto area, was on March 15 and 16. Since then, readings have steadily fallen. Radiation, which continues to be released at Fukushima Prefecture, have near normal radiation levels at all prefectures in the Kanto area.
According to figures by the Ministry of Education and Science (MES) for readings on April 10 of radiation levels, Gumma Prefecture has fallen into the normal radiation range while seven prefectures, including Fukushima, remain above it. There are normal levels at Saitama and Tokyo. On March 15 and 16 due to explosions at the Fukushima plant, readings soared above normal levels in 10 prefectures.
Even in Fukushima prefecture, Namieicho Aka Ustsugi, which recorded 170 µSV per hour on March 17, has fallen into the range of 25.2 µSv per hour on April 10. Total radiation from March 23 through April 9 was 13.9 milisieverts. In Fukushima City the highest recorded levels have fallen from 24.24 µSv to 1.8 µSV and in the village of Itatake from 44.7 µSv to 5.68 µSv.
Tokyo, which at the time recorded its highest level of 0.496 µSv, has fallen to 0.085 µSV within the range of highest average levels of 0.079 µSv. Utsunomiya is at a normal level of 0.075 µSv from a high of 1.318 µSv and Saitama City is at nearly normal levels of 0.066 µSv from a peak of 1.22 µSv.
Samples taken in the sea at 35 kilometers northeast from the Fukushima reactors showed levels of cesium 137 at 44.2 becquerels (*see footnote) were well below normal limits and were the highest levels recorded. However readings of Iodine 131 were above normal levels.
*The becquerel (symbol Bq) (pronounced: be-ˈkrel) is the SI-derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Bq unit is therefore equivalent to s−1. The becquerel is named for Henri Becquerel, who shared a Nobel Prize with Pierre and Marie Curie for their work in discovering radioactivity.