Because some radiation has escaped from nuclear power plants in Japan, and because they are in serious danger of a full melt-down, with any amount of radiation in between, it is recommended that you take about 65mg of potassium iodide daily for about 10 days. The link below shows the radiation path and timetable. KI protects the thyroid, which is the most affected by radiation.
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Nuclear fallout map. Might be a time to eat more sea veggies and take potassium iodine asap for a week or more?