Isotope in the news

Radioactive iodine, ¹³¹I, in the news.

Nuke agency reports unusual radiation in Europe Associated Press Vienna, Austria

The International Atomic Energy Agency says the "very low levels of iodine-131 have been measured in the atmosphere over the Czech Republic" and elsewhere on the continent.

Look at Webelements.com and see if you can tell why the last sentence in this article mentions a specific number of days.