Published On: Thu, Jul 28th, 2011

The Basics: What You Should Know About Radiation

radiation basics


What You Should

Know About Radiation


Japanese worker scrambled to control several nuclear plants and the meltdown of the Japanese nuclear fuel rods. Officials said that the readings at the Fukushima Daiichi nuclear plant were not at levels to cause “harm to human health,” and the potential for impending disasters continue. Here’s more on combating radiation sickness.

Radiation levels at one nuclear power plant in Japan were between 100 and 400 millisieverts. To put that in perspective, in the United States, a person typically gets a radiation dose of 6.2 millisieverts per year.

That dose would quickly dissipate with distance from the plant to pose no immediate public health threat due to radiation. Still, Japanese residents as far as 30 kilometers or 18.6 miles were warned to stay inside.

At the higher end of that spectrum at the Japan plant, exposure to millisieverts for three hours would lead to radiation sickness, and eight hours would be fatal, said Ira Helfand of Physicians for Social Responsibility. Keeping it below 500 millisieverts is pretty safe, said Nolan E. Hertel, nuclear engineering expert at Georgia Institute of Technology. Here’s a bit of basic science to help explain the science and harmful effects of radiation.

What is radiation and why radiation is so dangerous?

Atoms become radioactive when they are unstable at their nuclear or atomic levels. In a process called “radioactive decay,” the atom can split into smaller parts and release a lot of very harmful energy. The subatomic particles emitted during a radioactive decay include gamma rays, neutrons, electrons, and alpha particles. Some of these elements can piece straight through the human body, damaging cells and posing a significant hazard for humans.

Alpha particles are relatively heavy and, when emitted, cannot penetrate human skin or clothing. Alpha particle radiation is still harmful if they get into the body by other means. Beta particle radiation can cause skin injury and is also harmful internally. Gamma and X-rays are high-energy invisible light that can damage tissue and are the greatest threat.

Some elements such as uranium, commonly used as fuel in nuclear power plants, are always radioactive; there is no nonradioactive form of them that naturally occurs in nature.

Radiation from the Japanese power plant is getting into the atmosphere because of the explosions that have happened there, and because it is necessary to vent some of it in order to prevent further damage.

Measuring radioactivity

Radioactivity is measured by how many atoms are spontaneously disintegrating or “decaying” per second. Specific instruments are designed to detect particular kinds of radiation that get released with each decay. We use units of radiation exposure called rems or sieverts, which measure the biological effect of whole-body radiation. Geiger counters detect radiation emitted from decaying atoms.

Common sources of radiation

The average annual radiation exposure we get from natural sources is 3.1 Sometimes we get double that or a total of 6.2 millisievert exposure because of medical diagnostic procedures and other man-made sources of radiation. The limit for occupational radiation exposure among workers who deal with radioactive material is 50 millisieverts. Here’s more on common sources of radiation from the FDA. A chest X-ray delivers about 02 millisieverts, and a CT carries 8 millisieverts. See our article on the danger of CT scans. But these procedures take seconds and prolonged radiation exposure is much more dangerous and harmful.

Although high doses of radiation can lead to cancer, radiation therapy targeted at tumors is also used to treat cancer as a double negative (to destroy what is harmful). That dose is about 10,000 times the typical exposure rate for the U.S., but it is applied to the cancerous tissue; the total-body exposure during radiation therapy is less.

Radioactive danger level for humans

According to the NRC, scientists believe that half a population would die within 30 days after a full-body dose of 3,500 to 5,000 millisieverts from a few minutes to hours. The more than 130 plant workers and firefighters who developed acute radiation sickness at Chernobyl received doses of 800 to 16,000 millisieverts.

Populations exposed to high levels of radiation have shown the risk of cancer. High-dose radiation exposure, above 500 millisieverts, has been associated with leukemia, breast, bladder, colon, liver, lung, esophagus, ovarian, multiple myeloma, and stomach cancers, according to the United States Nuclear Regulatory Commission.

But there is less evidence linking low dose radiation, below 100 millisieverts, to cause cancer but it does exist. People who live in places that have higher levels of background radiation than normal, such as Denver, Colorado, slightly above 10 millisieverts per year, have not shown adverse biological effects. But higher “low level” background radiation might. Also the higher up you are in the atmosphere, the more radiation exposure (rays from the sun and other cosmic sources) – why airline pilots and flight attendants get more radiation than the average person.

Learn more about the basics of radiation from HPS – the Health Physics Society

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