Radiation Exposure

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Radiation exposure

Radiation is defined as the emission of energy from an atom in the form of a wave or particle. Such energy is released as electromagnetic radiation or as radioactivity . Electromagnetic radiation includes radio waves, infrared waves or heat, visible light, ultraviolet radiation , x rays, gamma rays, and cosmic rays. Radioactivity, emitted when an atomic nucleus undergoes decay, usually takes the form of a particle such as an alpha particle or beta particle , though atomic decay can also release electromagnetic gamma rays.

While radiation in the form of heat, visible light, and even ultraviolet light is essential to life, the word "radiation" is often used to refer only to those emissions which can damage or kill living things. Such harm is specifically attributed to radioactive particles as well as the electromagnetic rays with frequencies higher than visible light (ultraviolet, x rays, gamma rays). Harmful electromagnetic radiation is also known as ionizing radiation because it strips atoms of their electrons, leaving highly reactive ions called free radicals which can damage tissue or genetic material.

Effects of radiation

The effects of radiation depend upon the type of radiation absorbed, the amount or dose received, and the part of the body irradiated. While alpha and beta particles have only limited power to penetrate the body, gamma rays and x rays are far more potent. The damage potential of a radiation dose is expressed in rems, a quantity equal to the actual dose in rads (units per kg) multiplied by a quality factor, called Q, representing the potency of the radiation in living tissue. Over a lifetime, a person typically receives 7–14 rems from natural sources. Exposure to 5–75 rems causes few observable symptoms. Exposure to 75–200 rems leads to vomiting, fatigue, and loss of appetite. Exposure to 300 rems or more leads to severe changes in blood cells accompanied by hemorrhage. Such a dosage delivered to the whole body is lethal 50% of the time. An exposure of more than 600 rems causes loss of hair, loss of the body's ability to fight infection, and results in death. A dose of 10,000 rem will kill quickly through damage to the central nervous system.

The symptoms that follow exposure to a sufficient dose of radiation are often termed "radiation sickness" or "radiation burn." Bone marrow and lymphoid tissue cells, testes and ovaries, and embryonic tissue are most sensitive to radiation exposure. Since the lymphatic tissue manufactures white blood cells (WBCs), radiation sickness is almost always accompanied by a reduction in WBC production within 72 hours, and recovery from a radiation dose is first indicated by an increase in WBC production.

Any exposure to radiation increases the risk of cancer , birth defects , and genetic damage, as well as accelerating the aging process, and causing other health problems including impaired immunity. Among the chronic diseases suffered by those exposed to radiation are cancer, stroke, diabetes, hypertension, and cardiovascular and renal disease.

Sources of radiation

Some 82% of the average American's radiation exposure comes from natural sources. These sources include radon gas emissions from underground, cosmic rays from space, naturally occurring radioactive elements within our own bodies, and radioactive particles emitted from soil and rocks. Man-made radiation, the other 18%, comes primarily from medical x rays and nuclear medicine, but is also emitted from some consumer products (such as smoke detectors and blue topaz jewelry), or originates in the production and testing of nuclear weapons and the manufacture of nuclear fuels.

Environmental scientists believe that radon, a radioactive gas, accounts for most of the radiation dose Americans receive. Released by the decay of uranium in the earth, radon can infiltrate a house through pores in block walls, cracks in basement walls or floors, or around pipes. The Environmental Protection Agency estimates that eight million homes in the United States have potentially dangerous levels of radon, and calls radon "the largest environmental radiation health problem affecting Americans." Inhaled radon may contribute to 20,000 lung cancer deaths each year in the United States. The EPA now recommends that homeowners test their houses for radon gas and install a specialized ventilation system if excessive levels of gas are detected.

Though artificial sources of radiation contribute only a small fraction to overall radiation exposure, they remain a strong concern for two reasons. First, they are preventable or avoidable, unlike cosmic radiation, for example. Second, while the average individual may not receive a significant dose of radiation from artificial sources, geographic and occupational factors may mean dramatically higher doses of radiation for large numbers of people. For instance, many Americans have been exposed to radiation from nearly 600 nuclear tests conducted at the Nevada Test Site . From the early 1950s to the early 1960s, atmospheric blasts caused a lingering increase in radiation-related sickness downwind of the site, and increased the overall dose of radiation received by Americans by as much as 7%. Once the tests were moved underground, that figure fell to less than 1%.

A February 1990 study of the Windscale plutonium processing plant in Britain clearly demonstrated the importance of the indirect effects of radiation exposure. The study correlated an abnormally high rate of leukemia among children in the area with male workers at the plant, who evidently passed a tendency to leukemia to their children even though they had been receiving radiation doses that were considered "acceptable."

Recently, the EPA published their National Radon Results listing studies from 1984 to 1999. This study showed that 18 million homes have been tested for radon in the United States. In 1999 alone, there were about 1.4 million homes tested for radon. The knowledge of radon's harmful effects is on the rise (88% of Americans were aware of the harmful effects in 1999 compared to 73% in 1996) which is apparently contributing to the increase in testing.

[Linda Rehkopf and Jeffrey Muhr ]