|Don't breathe too deep, guys|
Recently foxnews.com presented an article that said that "About 1,500 people had been scanned for radiation exposure". Another article suggested that iodine serves as a treatment against radiation exposure, stating that "virtually any increase in ambient radiation can raise long-term cancer rates, and authorities were planning to distribute iodine, which helps protect against thyroid cancer." Both these articles have confused radiation and radioactivity.
Given that the reactors shut down shortly after the earthquake, the radiation they're worried about is gamma radiation. Like visible light, gamma radiation is composed of photons, although they have a much higher energy than photons of light. Unless a person receives enough exposure to show signs of radiation sickness, there's no easy way to determine if someone has been exposed to radiation. That's why nuclear workers wear dosimeters, which measure how much radiation a person has received. Nor does gamma radiation make things radioactive. A person could receive a lethal dose of radiation and yet their body wouldn't emit any radiation itself. Nor would an inanimate object become radioactive after being exposed to high levels of gamma rays. Neutron radiation, on the other hand, can cause a substance to become radioactive (this is called "activation"), but such high levels of neutron radiation are only encountered during an active fission or fusion reaction.
With regard to the general public, which was kept too far from the plant to have received dangerous levels of radiation exposure, what Japanese authorities are worried about is radioactivity (this is often called "radioactive contamination" or simply "contamination"). Radioactivity consists of particles of matter that emit radiation. A good analogy of radioactivity is burning charcoal; the charcoal is the radioactivity and the heat given off is the radiation. Confusing radioactivity with radiation is like confusing hot coals with the heat being produced.
|An actual anti-contamination suit|
This radioactivity would consist of various fission products such as radioactive isotopes of cesium, strontium, and iodine. The 1,500 people mentioned in the foxnews.com article were being scanned for radioactivity (particles of fission products) on their clothing, skin, or inside their bodies. This contamination is detectable through the radiation emitted by the radioactive particles that are on the victims or inside them. Since strontium is chemically similar to calcium and is absorbed by the bones, and iodine is absorbed by the thyroid, these substances can spend a long time inside the human body. Long term internal exposure to radiation can cause serious health problems. The reason why Japanese authorities were planning on distributing iodine (the non-radioactive form, of course) is because it saturates the thyroid and prevents it from absorbing the radioactive version that may have contaminated the environment.
|An "anti-radiation suit"|
would look more like this