Plutonium-241 of Fukushima Origin Found 32 Kilometers from the Plant, Says National Institute of Radiological Sciences After Nearly One Year

The National Institute of Radiological Sciences (NIRS) knew about it since May last year, but decided to keep quiet. Why? It's yet another case of the researchers waiting until their data collection is published in a peer-review scientific magazine (the paper is linked at the bottom of the post).

For the NIRS researchers, their data has just been published in the UK's Scientific Reports (electronic version), reports Kyodo News (3/8/2012):

放射線医学総合研究所（千葉市）は、東京電力福島第１原発から北西や南に２０～３２キロ離れた福島県内の３地点で、事故で放出されたとみられるプルトニウム２４１を初めて検出したと、８日付の英科学誌「サイエンティフィック・リポーツ」の電子版に発表した。

The National Institute of Radiological Sciences (NIRS, in Chiba City, Chiba) published the result of their measurement of plutonium-241 at three locations in Fukushima Prefecture 20 to 32 kilometers northwest and south of Fukushima I Nuclear Power Plant in the electronic version of the UK's science magazine "Scientific Reports" issued on March 8, 2012.

　人体に影響のないレベルだが、プルトニウム２４１は他の同位体に比べて半減期が１４年と比較的短く、崩壊してできるアメリシウム２４１は土壌を経由して主に豆類に取り込まれやすい。放医研は「内部被ばくを避けるためにも 原発２０キロ圏内での分布状況を確かめる必要がある」としている。

The level [of plutonium-241] will not affect human health. Plutonium-241 has relatively short half life of 14 years compared to other isotopes of plutonium. It decays into americium-241, which is easily absorbed through soil into legumes. The NIRS says "To avoid internal radiation exposure, it is necessary to survey the spread of plutonium-241 inside the 20 kilometer zone around the plant."

　昨年４～５月に採取した福島県飯舘村、浪江町の森林の落ち葉と、スポーツ施設で現在事故対応拠点となったＪヴィレッジ（広野町など）の土から検出。他の同位体プルトニウム２３９（半減期２万４千年）、２４０（同６６００年）も検出 、同位体の比率から今回の事故が原因と分かった。

[Plutonium-241] was detected from the samples they collected in April and May last year - the dead leaves from the forests in Iitate-mura and Namie-machi, and the soil at J-village, which has been used as the staging area for the work after the Fukushima I Nuke Plant accident. Other isotopes of plutonium, plutonium-239 (half life 24,000 years) and plutonium-240 (half life 6,600 years), were also detected. From the ratio of isotopes, the NIRS researchers concluded that they were from the Fukushima nuclear accident.

　濃度は、過去に行われた大気圏内核実験の影響により国内で検出されるプルトニウム２４１よりも高い。ただ半減期が短く、１９６０年代当時に核実験で飛来した濃度よりは低いレベルという。

The density of plutonium-241 [detected this time] is higher than that being detected in Japan after the atmospheric nuclear tests in the past. However, plutonium-241 has a short half life, and the density is lower than that during the 1960s when the radioactive fallout from the nuclear tests fell on Japan.

　プルトニウムは天然にはほとんど存在しない放射性物質で、原子炉では燃料のウランが中性子を吸収してできる。

Plutonium is a radionuclide that hardly exists in nature. It is created when uranium in the reactor fuel absorbs neutrons.

Hmmm. If you want to avoid internal radiation exposure by ingesting food that may contain americium-241, a decay product of plutonium-241, don't you want to survey the area outside the 20 kilometer zone? After all, outside the 20 kilometer zone, Fukushima farmers will be tilling the land, ready to grow crops of all kinds again this year.

Half life of americium-241 is 432.7 years. As it decays, americium-241 emits alpha and gamma rays.

Asahi Shinbun has the numbers for plutonium-241:

• Dead leaves in Namie-machi (26 kilometers NW of the plant): 34.8 becquerels/kg

• Dead leaves in Iitate-mura (32 kilometers NW of the plant): 20.2 becquerels/kg

• Soil at J-Village (20 kilometer south of the plant: 4.52 becquerels/kg

Farmers in Fukushima, are you still going to grow stuff on your land?

Researchers at the NIRS, did you think of at least informally telling the local authorities or the farmers about your findings? Or did you just sit and wait until your paper was published by a peer-review magazine?

(I know I'm wasting my breath.)

Scientific Reports carries their full paper online.

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