Japan Radiation Leak: Exposure & Sickness?

Japan endured not only a magnitude 8.9 earthquake but also radiation leaks from several nuclear reactors.
Concerns are growing in Japan over the increased levels of exposure to radiation detected around the nuclear plants.

New explosions at the Fukushima plant, released low levels of radiation, worsening Japan's nuclear crisis.
What are the risks of sickness right now due to the exposure to radiation? Is the United States going to be affected by the radiation leak in Japan?

Japanese nuclear experts have been struggling to contain the aftermath of fires, explosions and radiation leaks.
Public health officials in the U.S. are trying to reassure residents that the radiation from Japan will pose no threat to the United States coast.

There are two main fears: the release of radioactive iodine which can cause serious sickness like thyroid cancer and the release of cesium, which is what happened at Chernobyl.
While radiation exposure and sickness here in the U.S. is unlikely, some pharmacists say they can't keep potassium iodide tablets on their shelves.