But the Ministry of Education (MEXT) doesn't think the strontium-90 fallout after May last year was of Fukushima origin.
Following up on the post about strontium-90 fallout last year that MEXT (Ministry of Education and Science) announced on July 24 this year, I found some interesting data in the Japan Chemical Analysis Center where I created the chart plotting the Sr-90 fallout for the past 50 years or so in Japan (reproduced here).
The 2011 monthly fallout data for strontium-90 at the Japan Chemical Analysis Center is easier to see than the MEXT PDF file pages (they are the same data). As I was browsing through the search result, I started to wonder:
When was the last month that strontium-90 was detected in the fallout for these ten prefectures?
So here it is, from the search result at the Japan Chemical Analysis Center's website, the last date when strontium-90 was detected in the monthly fallout in the cities/prefectures in Tohoku and Kanto in 2011:
Aomori City, Aomori: March 31
Morioka City, Iwate: September 10
Akita City, Akita: July 1
Yamagata City, Yamagata: July 1
Hitachinaka City, Ibaraki: November 1
Utsunomiya City, Tochigi: August 1
Maebashi City, Gunma: June 1
Saitama City (Sakura-ku), Saitama: August 1
Ichihara City, Chiba: November 1
Chiba City (Inage-ku), Chiba: November 1
Shinjuku-ku, Tokyo: August 1
Chigasaki City, Kanagawa: June 30
Of these results, MEXT doesn't seem to think the detection in Aomori had anything to do with the Fukushima nuclear accident, as the prefecture is excluded from the list by MEXT in the press release (see my previous post for the MEXT list). In addition, MEXT seems to think the fallout after the first two to three months of the accident (March through May, 2011) is due not to the Fukushima accident but to the past atmospheric nuclear testing because the measured amount did not exceed the amount prior to the Fukushima accident.
Outside Kanto and Tohoku regions, there are occasional detection of strontium-90 in:
Niigata City (Nishi-ku), Niigata: May 2
Imizu City, Toyama: April 1
Kakamigahara City, Gifu: July 1
Shizuoka City (Aoi-ku), Shizuoka: August 1
Yokkaichi City, Mie: May 2
Kyoto City (Fushimi-ku), Kyoto: April 1
Wakayama City, Wakayama: November 1
Okayama City (Minami-ku), Okayama: April 1
Ishii-cho (Myozai-gun), Tokushima: April 1
Takamatsu City, Kagawa: April 1
Matsuyama City, Ehime: April 1
Kochi City, Kochi: April 1
Likewise, none of the detections above is considered by MEXT as the result of the Fukushima accident.