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| C. moniliferum, Crystallizing StrontiumMinna R. Krejci et al. via CHEMSUSCHEM |
Showing posts with label Nuclear Radiation. Show all posts
Showing posts with label Nuclear Radiation. Show all posts
Algae Could Be The Key to Cleaning Up Nuclear Accident Sites
How Does Nuclear Radiation Do Its Damage?
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| Officials in protective gear check for signs of radiation |
Ionizing radiation—the kind that minerals, atom bombs and nuclear reactors emit—does one main thing to the human body: it weakens and breaks up DNA, either damaging cells enough to kill them or causing them to mutate in ways that may eventually lead to cancer.
After last week’s earthquake and tsunami in Japan, four nuclear reactors at the Fukushima Daiichi plant are now damaged and releasing radiation. Workers trying to keep the reactors from getting worse are themselves being exposed, while the Japanese government has called for anyone within 20 kilometers of the plant to evacuate.
Nuclear radiation, unlike the radiation from a light bulb or a microwave, is energetic enough to ionize atoms by knocking off their electrons. This ionizing radiation can damage DNA molecules directly, by breaking the bonds between atoms, or it can ionize water molecules and form free radicals, which are highly reactive and also disrupt the bonds of surrounding molecules, including DNA.
Peter Dedon, a member of the Radiation Protection Committee at MIT, explains: “What happens is that the nucleus of radioactive elements undergoes decay and emits high-energy particles. If you stand in the way of those particles, they are going to interact with the cells of your body. You literally get a particle, an energy packet, moving through your cells and tissues.”
If radiation changes DNA molecules enough, cells can’t replicate and begin to die, which causes the immediate effects of radiation sickness -- nausea, swelling, hair loss. Cells that are damaged less severely may survive and replicate, but the structural changes in their DNA can disrupt normal cell processes -- like the mechanisms that control how and when cells divide. Cells that can’t control their division grow out of control, becoming cancerous.
With ingested particles, some may pass through the body before they do much damage, but others linger, Dedon says. Radioactive iodine-131 poses a particularly significant risk, because it is absorbed rapidly by the thyroid gland and held there. That is why it is recommended that those who may be exposed to radioactivity in the air pre-dose themselves with iodine pills: the non-radioactive iodine is absorbed by the thyroid, which then does not absorb radioactive iodine if it comes along.
Radiation exposure risk is measured in units called sieverts, which take into account the type and amount of radiation, and which parts of the body are exposed, allowing us to compare different kinds of exposures in one scale.
In a typical year, a person might receive a total dose of two or three millisieverts from things like ambient radioactivity, plane flights and medical procedures. In the U.S. the annual exposure limit for nuclear plant workers is 0.05 sieverts per year. At or below these levels, the enzymes that repair DNA keep up with damage enough to keep the risk of cancer low. Above them, the body’s systems of repair can’t keep pace. 100 millisieverts a year is the threshold above which cancer risk starts to increase, according to the World Nuclear Association.
According to reports, radiation levels have fluctuated at Fukushima, rising at one reading to 400 millisieverts per hour. At that level, Dedon says, seven minutes would bring you to the U.S. yearly limit. Over an hour could be a lethal dose. The 400 millisieverts level was not a sustained measurement and levels continue to fluctuate much lower.
Dedon stresses that because radiation dissipates, like light, by the square of its distance, even if levels are high in the plant, just a few miles away, they would be miniscule. The greater danger for people living in the area is the release of radioactive particles into the air, which can accumulate in the body, damaging tissue over time and causing cancer.
Receiving a one-sievert dose of radiation in a day is enough to make you feel ill, according to Dedon. “At one to three, you have damaged bone marrow and organs, and you’ll really be sick. At three to six you add hemorrhaging, and more infection,” he says. “From six to ten, at that level death is something like 90 percent. And above ten, they just call that incapacitation and death.”
Source: Popsci
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 produces energy via fission of uranium-235, which means it splits uranium-235 into smaller atoms. Two types of these smaller atoms, cesium-137 and iodine-121, were found about sixty miles 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 even smaller atoms, and 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 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 through living material, which means any tissue in your body can be exposed to them. Gamma radiation is called ionizing 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 your 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 ionization that the cells experience.
Low level ionization just causes some cells to be slightly damaged. This kind of damage is much the same as a sunburn. A sunburn is caused by 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 your cells. This damage can cause your DNA to mutate, or behave abnormally. Ionization can also cause trouble when exposed cells divide - they may keep dividing without limit, causing cancer.
Higher levels of radiation have more immediate effects. Often the cells lining the intestines are damaged, and the body can't absorb 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 aluminum 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. Another 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.
Radioactive materials are also tough to contain. Although they can be measured, and scrubbed off, they are made of 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 gray, which is a ratio of the amount of material absorbed to the mass of the matter that absorbed it. One gray 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 defense 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.
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