The big worries on the reported releases of radioactive material in Japan center on radioactive iodine and cesium.

在日本报道的放射性物质泄漏中，最令人担忧的主要是放射性碘和铯。

youdao

Radioactive iodine has a half-life of eight days and decays naturally within weeks.

放射性碘的半衰期为八天，几周内自然衰变。

youdao

Some of the initial food monitoring results show radioactive iodine detected in concentrations above the Japanese regulatory limits.

食品监测的初步结果表明，放射性碘的浓度已经超出日本规定的限度。

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On Tuesday, Chinese officials reported low levels of radioactive iodine-131 in areas of southeastern China.

VOA: special.2011.03.30

But people exposed to high levels of radioactive iodine can get thyroid cancer.

VOA: special.2011.03.30

The pills flood the thyroid gland with non-radioactive iodine.

VOA: special.2011.03.30

Radioactive iodine treatment uses large doses of a form of iodine that's radioactive.

CNN: Thyroid cancer

Radioactive iodine caused thousands of cases of thyroid cancer in children after the Chernobyl accident.

FORBES: Reports Claim Meltdown At Japanese Reactor

Radioactive iodine-131 and cesium-137 were also found in the drainage outlet of units 5 and 6.

FORBES: The Japanese Nuclear Power Crisis Deepens