Americans scared of radiation from Japan's nuclear power plants are making a run on radiation poisoning pills.
However, the U.S. Nuclear Regulatory Commission said there is little threat here from Japanese radiation. That is because of the distance, which, along with the fact that radiation decays over time, are crucial factors.
Radiation is measure in "Grays" or Gy for short. A chest X-Ray exposes you to less than .1 Gy. One whole Gy can cause symptoms. 6 Gy's can cause death in 2 days to 2 weeks.
Since Gy's are hard to measure, doctors often go by symptoms which are very time specific.
If it's low dose it may cause nausea and vomiting in 6 hours, but usually causes no other symptoms.
There is no reason to be fearful here in Southern California. Even if you came into contact with someone who came from Japan, especially if they have changed clothing and washed up.