How Does Radiation Travel, And What Kinds Of Damage Can It Do?

The nuclear disaster in Japan has left many people in danger of exposure to radiation and radioactivity. Some are simply fearful. What exactly is this radiation? And what threat does it pose? We've got some answers below.

What is radiation?

Radiation has become a frightening word, but there's not necessarily anything dangerous about it. Visible light is radiation. Heat is radiation. Many news channels say that explosions or meltdowns 'leak' radiation into the atmosphere, but few say what exactly this 'radiation' is.

At least one of the explosions at the nuclear power plants has vented steam that contains radioactive materials. The nuclear power plant produce energy by fission of uranium-235, the split of uranium-235 into smaller atoms. Two types of these atoms, cesium-137 and iodine-121 were found about 100km from the Fukushima Daiichi power plant. These radioactive materials can't be detected biologically, and so can be rubbed on the skin, eaten, or breathed in. These atoms break down into smaller even smaller atoms, or their neutrons can change to protons. When this happens, they give off highly energetic gamma rays.

They also give out beta radiation. Beta particles are basically ejected electrons. Although they are not as energetic as gamma rays, they can cause skin problems if left on the skin for a prolonged time. Since radioactive materials can be ingested, beta particles can also be ejected inside the human body, where they can do a lot of damage.

What does radiation do?

Gamma rays are the highest energy rays in the electromagnetic spectrum. They are so energetic that they can travel great distances through the air or other material, and can pass entirely through living material, which means any tissue in body can be exposed. Gamma radiation is called ionising radiation. When it encounters an atom, it can rip the electron right off, leaving an ion behind.

Once an atom becomes an ion, it reacts to the world around it in a different way. It can be attracted to certain things, repelled by others, or even join together with another atom. Since the living tissue is set up to work with non-ionic forms of atoms, introducing an ion into a part of the body where it doesn't belong has drastic consequences. Sometimes it only damages cells, but often it kills them off entirely. The effect depends on the level of ionisation that the cells experience.

Low level ionisation just causes some cells to be slightly damaged. This kind of damage is much the same as a sunburn. A sunburn is caused by the relatively mild UV radiation, and only affects exposed areas of skin. Gamma radiation can burn any area of the body, and burns resulting from it are usually much more severe than sunburns. Although low level radiation exposure may not have any immediate effects, the damage can be done to the DNA inside the cell, causing the DNA to either be sequenced or expressed abnormally. Ionisation can also cause trouble when exposed cells divide - they can keep dividing, causing cancer.

Higher levels of radiation have more immediate effects. Often the cells lining the intestines are damaged, and the body can't take in water or nutrients. Bone marrow can also be affected. Without these, the body has a hard time fighting off external infections or diseases, and many victims of radiation die of infection. If, however, medical professionals are able to keep them alive and ward off infection, their bodies can recover.

Even higher levels of radiation exposure do damage to the vascular system. This damage is extensive and can cut off the flow of blood to vital organs like the brain. When the damage is this severe, there is nothing that medicine can do to help the person affected. This level of radiation is almost always fatal.

Beta radiation is also very dangerous. The isotope iodine-131 is a particular worry because of its beta radiation and its placement within the body. Iodine-131 tends to bind to the thyroid. When it decays, the ejection of beta particles tends to harm fast-dividing cells. Since children are still growing, their cells are dividing particularly fast and are very vulnerable. Too much exposure can cause thyroid cancer.

How does radiation travel?

Gamma rays travel like any other electromagnetic waves - cutting a fairly straight line through world. They can move through a vacuum, or through air or water. They can also cut through light elements like aluminium or most metals. Lead can cut down on gamma radiation, but it can't really stop it. One inch of lead will cut any amount of gamma radiation by half. Anothe inch will cut it by another half, and so on, and so on. Practically speaking, a few feet of lead will weed out pretty much any gamma radiation, but technically nothing can block all gamma rays from coming through.

Radiactive materials are also tough to contain. Although they can be measured, and scrubbed off, they are tiny, invisible atoms. Once they are released into the air, they can get blown by the wind or rain down on the land, get absorbed or eaten by plants and animals, adhere to matter, and scatter out through the world.

How much radiation is dangerous?

Radiation is difficult to measure. Exactly how much radiation anyone has been exposed to depends on the material they were exposed to, the distance they were from that material, and the time period they were exposed for. Absorbed doses of radiation are measured in a unit called a grey, which is a ratio of the amount of material absorbed to the mass of the matter that absorbed it. One grey is one joule of energy released into one kilogram of absorbing matter.

Many nuclear agencies prefer to measure the amount of radiation absorbed in sieverts. A sievert takes into account the type of energy released, as well as the way it was transmitted, and how vulnerable the absorbing tissue is to radiation. The typical exposure to radiation is measured in millisieverts, or thousandths of a sievert. Generally, people are exposed to about 3 millisieverts of radiation per year. An X-ray gives people 4 millisieverts, a CT scan gives 10. A dose of five hundred millisieverts ushers in radiation sickness, while exposure to one sievert gives the victim a ten percent chance of death within 30 days.

When the Fukushima plant was at its worst, it was giving out radiation at a rate of about 400 millisieverts per hour. That meant that most workers needed to be evacuated immediately. Fortunately, the level went down to about .6 millisieverts an hour. Levels of radiation throughout the area continue to be monitored.

Is there any way to avoid or treat radiation exposure?

The best way to avoid radiation exposure is to take steps to avoid materials contaminated with radioactive atoms. Distance is best - about 70,000 people have been evacuated from around the Fukushima plant. Clean food and clean water are also key. Families in the area of the plants are being encouraged to stay inside, to jam blankets and clothes in doors, and eat canned food.

The best defence people currently have only works against iodine-131. Since the thyroid absorbs iodine, and since it can be saturated with the stuff, children around the affected area are being given tablets containing normal iodine. When they eat them, the thyroid becomes filled with regular iodine, and can't take any more in, blocking the radioactive iodine from lodging in the body. Since iodine-131 has a half-life of eight days, the danger is temporary and can be staved off. Beyond that, there isn't much to be done about radiation exposure except treating the symptoms and getting screened for cancer regularly.

Although the danger is still great, most residents of Japan are being asked to stay calm. As are people elsewhere. The high level of radiation being given off by the Fukushima plant was a one time emission, and is unlikely to greatly affect residents of Tokyo, let alone residents of other countries. Radiation is to be avoided as much as possible, but it's also part of daily life.

Via Scientific American, NY Times, EPA, GM, CDC, Sievert Systems, and The Independent.

Top image by Pindyurin Vasily/Shutterstock

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