Friday, January 3, 2014

原子力事故後の野菜汚染と除去法  Vegetable contamination and decontamination after Nuclear accident

Evaluation of vegetables in Tsukuba for contamination with radioactive materials from the accident at Fukushima Daiichi nuclear power plant.

Abstract (要約)

A large amount of radioactive material was released into the atmosphere after the accident of the Fukushima Daiichi Nuclear Power Plant following the Tohoku earthquake on 11 March 2011, and traces of these materials were detected in Tsukuba. Because radioactive materials can adhere to vegetables, the authors made a qualitative evaluation of vegetables in Tsukuba, estimated internal exposure dose based on quantitative measurement results, and investigated several decontamination methods.

Qualitative analysis of vegetable contamination was done by autoradiography. Quantitative analysis was done using a high-purity germanium detector.

To assess decontamination, two methods were tested: one with running water and the other with boiling water. In addition, boiled soup stock was measured.

In the qualitative evaluation by autoradiography, radioactive materials were not uniformly distributed but adhered to vegetables in clumps and hot spots. In the quantitative evaluation to measure contamination of outer and inner leaves of sanchu lettuce, it was observed that the concentration of I was 8,031.35 ± 764.79 Bq kg in the outer leaves and 115.28 ± 20.63 Bq kg in the inner leaves. In addition, the concentration of Cs was 1,371.93 ± 366.45 Bq kg in the outer leaves and 9.68 ± 15.03 Bq kg in the inner leaves. This suggests that one can greatly reduce internal exposure dose by removing the outer leaves if one has to eat vegetables just after a nuclear accident.
オートラジオグラフ法による質的評価では、放射性物質は均等に分布しておらず、野菜に固まってホットスポットがある状態で付着していた。量的評価では、レタスの外側の葉と内側の葉を測定し、外側の葉のヨウ素の濃度が8,031.35 ± 764.79 Bq/kg、内側の葉の濃度は 115.28 ± 20.63 Bq/kgだった。セシウムは、外側の葉が1,371.93 ± 366.45 Bq/kgで、内側の葉は9.68 ± 15.03 Bq/kgだった。つまり、原子力事故のあとで野菜を食べなければならない場合、外側の葉を取り除くことで内部被曝を大幅に減少させることができる

In the decontamination assessment, a decontamination efficiency of up to 70% was achieved by boiling vegetables for 20 min.

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