ラジウムか? 東京・豊島の公園から高放射線量の土の塊

東京都豊島区の公園で高い放射線量が検出され、同区は24日、土の中から高い放射線を出していた塊を採取、放射性物質ラジウムが含まれている可能性が高いとみている。
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EPA時事

東京都豊島区の公園の敷地内で毎時最大で480マイクロシーベルトと高い放射線量が検出され、豊島区は4月24日、原因の特定に向けた調査を行った。土の中から高い放射線を出していた塊を採取、区は放射性物質ラジウムが含まれている可能性が高いとみて、さらに分析を進める。朝日新聞デジタルなどが報じた。

区によると、掘り起こしたのは「池袋本町電車の見える公園」の大型遊具の下の表土。地表近くから塊(直径20センチ、厚さ10センチ)が出てきた。日本アイソトープ協会が測定すると、同500マイクロシーベルトを記録した。40時間いれば、国が避難の目安とする年間20ミリシーベルトに達する。(中略)

塊を取り除くと、掘った穴の放射線量は0・06マイクロシーベルトまで下がった。協会が今後、塊を詳しく調べて放射性物質の種類を特定する。

高放射線量の公園からラジウム含む?土の塊 東京・豊島:朝日新聞デジタル 2015/04/24 22:10)

高い放射線量が検出されたのは、子供向け遊具近くの地表で、区は公園を立ち入り禁止にした。安全が確認されれば禁止を解除することにしている。

区によると、公園は以前は東京都清掃局のごみ収集車の駐車場として使われてていたが、2008年に更地になり、2011年に区が土地を取得した。その際、土の入れ替えはしなかったという。

ラジウムは、コトバンクなどによると、1898年、フランスのキュリー夫妻がウラン鉱石から発見した最初の放射性元素。銀白色の金属で、放射線源として用いられた。天然物質で、以前はがん治療用の針や夜光塗料などにも使われていた。

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