新聞週間特集：「原発事故と報道」報告（その２止） 放射線知る一助に

(Mainichi Japan) October 21, 2011
Journalists strived to get truth about nuclear fallout to public (Part 2)
新聞週間特集：「原発事故と報道」報告（その２止）　放射線知る一助に

　◇累積線量、独自算出し掲載

The question of how much and where radioactive materials were dispersed by the hydrogen explosions at the Fukushima No. 1 nuclear plant have been of the utmost importance to residents of both Fukushima Prefecture and beyond, and one we began to pursue soon after the nuclear disaster started to unfold.
　福島第１原発事故から水素爆発などにより放出された放射性物質は、どのような範囲にどれくらい広がったのか。周辺地域の住民にとって最大の関心事であり、事故直後から力を入れて取材した。

The government initially designated the area within a 20-kilometer radius of the power plant an evacuation zone, while those living between 20 kilometers and 30 kilometers from the plant were instructed to remain indoors. 　政府は当初、原発から半径２０キロを避難区域、２０～３０キロを屋内退避区域に指定していたが、

However, high levels of radiation were being detected even beyond those areas.
その外側でもかなり高い放射線量が計測されていた。

A long-term advisory to stay indoors had not been a part of the government's disaster preparedness guidelines, and would pose too great a burden on residents.
長期間の屋内退避は防災指針でも想定していない事態で、住民への負担が大きすぎる。

It seemed to us that a designation of evacuation zones based on actual radiation measurements was necessary.
実際の放射線量に応じた避難区域の設定が必要だと感じていた。

That was when we came up with the idea of calculating cumulative radiation levels at various locations.
　そこで考えついたのが、各地の累積放射線量の算出だった。

At the time, radiation monitoring results released by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and municipal governments were limited to the amount of radiation detected in the atmosphere per hour (dosage rate).
当時、文部科学省や自治体の放射線モニタリング結果は、１時間当たりの大気中の放射線量（線量率）しか公表されていなかった。

But since local residents would continue to be exposed to radiation, we felt it far more important to provide information on cumulative radiation levels.
しかし、放射線を浴び続けることを考えれば、積算した線量の情報こそが重要だ。

When we appealed to MEXT to provide this information, we were told it was not something they could do right away.
文科省に取材したが、「すぐには出せない」との回答だったため、

It was decided then that the Mainichi would crunch the cumulative radiation level numbers by adding together dosage rates released by public sources.
線量率を足し合わせて独自に算出した。

Between March 14 and March 21, the cumulative radiation level in the city of Fukushima reached 1770.7 microsieverts.
　３月１４～２１日の積算値が福島市で１７７０・７マイクロシーベルトになったほか、

The figure was 299.7 microsieverts for the Fukushima prefectural city of Iwaki and 34.1 microsieverts for the Tochigi Prefecture capital of Utsunomiya for the same period, and 33.2 microsieverts in the Ibaraki Prefecture capital city of Mito between March 15 and March 21.
福島県いわき市２９９・７マイクロシーベルト▽宇都宮市３４・１マイクロシーベルト▽水戸市３３・２マイクロシーベルト（同市のみ１５～２１日）－－などとなった。

Having found the cumulative radiation in the city of Fukushima to exceed the average 1500 microsieverts of natural background radiation that we are normally exposed to annually, the Mainichi's Science and Environment News Department debated what to do with the information, concerned about the public response the information could spark.
特に福島市の値は、１年間に自然に浴びる放射線量（平均約１５００マイクロシーベルト）を上回っていたため、住民の不安感情を考え、部内で議論した。

Ultimately, we decided to release the information along with the explanation that cumulative radiation levels indicate how much radiation one would be exposed to if they stayed outdoors all day, and that radiation levels in general were trending downwards.
その結果、あくまで一日中屋外にいた場合の数値であり、線量は減少傾向にあることなどを明記し、

We also added commentary from multiple experts that the radiation levels posed no health risks for people "stepping out to shop" for groceries, and published the information in the March 23 morning issue of the Mainichi's Japanese edition.
「買い物などに出るのは問題ない」などという複数の専門家の見方を付け加えて、３月２３日の朝刊に掲載した。

Following publication, we received inquiries from various municipal governments in Fukushima Prefecture, and were criticized by some readers for "causing panic among Fukushima city residents."
　掲載後、福島県内の自治体担当者から問い合わせがあったほか、読者の一部から「福島市民を動揺させる」との批判も受けた。

We maintain, however, that by contributing information on cumulative radiation levels -- which until then had been largely ignored -- we helped residents come to their own conclusions on what to do next.
しかし、それまであまり考慮されていなかった累積放射線量の情報を提供し、住民自身に自分の行動を判断してもらう一助になったのではないかと思っている。

On March 25, MEXT began releasing cumulative radiation figures.
３月２５日になって文科省は累積放射線量の公表を開始。

Since then, it has gone on to conduct detailed monitoring of radiation levels, and has posted predicted cumulative radiation levels through March 2012.
その後、詳細なモニタリングを実施、来年３月までの１年間の累積線量予測値も公表した。

　◇的確な警告できず悔い

We still regret not having been able to predict that radioactive contamination would spread to the extent that it has.
　一方、放射性物質の汚染がこれほど広がることを予測できなかったことに悔いが残る。

We keep asking ourselves if there was any way we could've sounded a more precise alarm when large volumes of radioactive materials were released on March 14 and March 15, as we continue working toward protecting the public from unnecessary exposure.
特に３月１４、１５日の大量放出の際、もっと的確に警告を発することができなかっただろうか。住民の無用な被ばくを防ぐという視点を忘れず、取材を続けたい。

＜東京科学環境部・西川拓＞
(By Taku Nishikawa, Science and Environment News Department)

(This is part two of a six-part series on coverage of the Fukushima nuclear crisis.)
毎日新聞　2011年10月18日　東京朝刊