Sunday, March 13, 2011

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 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 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.


  1. Hey, interesting read, just bought a car from Minami Soma, a town that was evacuated, wanted to check if the engine would run on its own absorbed gamma rays, be more efficient that way. Damn, it won't, your article cleared that up.

  2. Hi James,

    Just read your article from 2011, hope you still see this comment... so are you saying if I bought an item (inanimate object) from Japan that is near where the nuclear reactors are, they would not emit radiation because they are not radioactive? Thanks... I am just concerned because I recently bought something from the Miyagi Prefecture and I found out it is actually nearby to Fukushima...

    1. Unless an item is exposed to significant neutron radiation (e.g., it's inside a reactor) it will not emit radiation by itself. However, it's possible for radioactive particles from a reactor to coat an item or to get inside of it. We call this radioactive contamination. Fortunately, it's extremely unlikely that your item would have detectible levels of radioactivity.

      During a nuclear accident like Fukushima, radioactivity is spread by an explosion and/or fire. Microscopic radioactive particles or gases that used to be in the reactor become airborne and form what we call a "plume". In the case of a fire, the particles are usually mixed in with the smoke. Like any other smoke particles, the radioactive particles eventually fall to earth, sometimes miles away from the accident.

      An item manufactured from Miyagi Prefecture could become radioactive only if microscopic radioactive particles blown out of the reactors ended up on the outside surface or were trapped inside it. The only real way the item could have ended up with significant levels of radioactivity on it would be if it were left outside while a plume passed overhead.

      The worst case scenario would probably be an earthenware pot made from local soil that lay in the path of the plume. In that case, it could potentially contain trace amounts of Cesium-137 and Strontium-90.

      However, in either case you are extremely unlikely to find levels of radioactivity that would pose a health hazard. You'll receive significantly more radiation exposure from medical procedures, airline flights, foods containing a lot of potassium, granite countertops, and naturally occurring radon collecting in your basement (which poses a genuine hazard).

    2. Wow, thanks for your detailed reply! ya...that's what I was concerned about, some radioactive particles landed or got into my item... i put it in my room, so i don't want to be sleeping in the room with it the whole time for years without knowing and then slowing getting exposed to it. But based on what you said, I guess I should feel at ease as I doubt the item was outdoors while the plume passed by...most likely it's inside a store or a warehouse...unless the air vents sucked the particles inside.
      I really appreciate your informative reply btw! =) Thanks so much for your help!!!



Related Posts with Thumbnails