Radioactivity Versus Radiation: Getting a Couple Things Straight

Don't breathe too deep, guys

I've been closely following the troubles that Japan has been having with a couple reactors since the earthquake and subsequent tsunami struck the area. As usual, I'm amazed at the misconceptions that the news media continues to spread. I'm talking specifically about the difference between radioactivity and radiation.

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

As of this blog post there have been two explosions at the nuclear plant. Under the right conditions, high levels of radiation inside the reactors can turn cooling water into gaseous oxygen and hydrogen. Apparently the Fukushima plant operators vented the gases from the reactors, which then exploded outside of the vessels (better outside the reactors than inside). Japanese authorities are worried that the combination of damaged fuel rods, gas venting, explosions, and potential breaches in the reactor vessels may have spread radioactivity in the region around the plant. People that are several miles away are relatively safe from the radiation being emitted by the damaged reactors, but they may fall victim to radioactive materials blown into the air by the explosions.

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

It's because of the media's and the general population's misunderstanding of the difference between radiation and radioactivity that I keep having to explain to people that there's no such thing as an "anti-radiation suit". The yellow anti-contamination suits (sometimes called "anti-Cs") that people may be familiar with are designed to protect the wearer from radioactivity. The yellow fabric is an impermeable material that prevents radioactivity from getting onto the wearer's skin. Where contamination may be found in the air, a respirator is worn to prevent inhalation of the material. These suits do not protect the wearer from external radiation. People in anti-Cs are as concerned about radiation as someone in street clothes. Radiation can only be shielded by dense materials like steel or lead or by generous layers of water or concrete. A steel or lead suit that could reduce radiation levels reaching the wearer by 90% would need to be several inches thick and would probably look like something from Iron Man.