Radiation Exposure

Radiation is the emission of energy from an atom in the form of a wave or particle.

Radiation is emitted when an atomic nucleus undergoes decay (change), which is associated with the radioactivity of certain naturally occurring and manmade isotopes. The radiation emitted through the radioactive decay of certain atomic nuclei consists of electromagnetic waves, or sub-atomic particles, or both. Electromagnetic radiation includes radio waves, infrared waves (or heat), visible light, ultraviolet radiation, x-rays, and gamma rays. Radioactivity usually takes the form of a sub-atomic particle such as an alpha particle or beta particle, although atomic decay can also release electromagnetic gamma rays.

Radiation is used safely in medical settings as both a diagnostic tool and a therapeutic agent. X rays are the most common diagnostic tool that uses radiation. Radioactive substances are also used as a diagnostic tool in nuclear medicine. A low-dose radioactive tracer substance is injected in the body. The physician can then trace the radioactivity as it moves through the bloodstream and collects in various tissues. The physician then evaluates whether the distribution of the radioactivity is normal or abnormal and from this can derive information about the patient's condition. Diagnostic radiation has a low risk of harming the patient.

A much higher dose of radiation is used as a therapeutic agent to kill cancer cells. High-energy gamma rays, x rays, or electrons are aimed at the cancerous tissue. These rays kill both cancer and normal cells, so the dose and length of exposure must be carefully calculated. Radiation therapy often is used in conjunction with chemotherapy or after surgery to remove malignant tissue.

About 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.

Manmade radiation, the other 18%, comes primarily from medical x rays and nuclear medicine, but it is also emitted from some other sources (e.g., smoke detectors; airport body scanners; blue topaz jewelry), or originates in the production and testing of nuclear weapons and the manufacture of nuclear fuels.

Although 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 exposure to 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.”

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. In 2010, the Environmental Protection Agency (EPA) estimated that roughly one in every fifteen homes in the United States had elevated levels of radon. The EPA called radon “the largest environmental radiation health problem affecting Americans.” Inhaled radon may contribute to as many as 21,000 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. Some states require radon testing whenever an existing house changes ownership.

The 2008–2009 report from the President's Cancer Panel recognized the health danger and ubiquitous nature of radon gas in the United States. The Panel offered a number of recommendations, such as a requirement of radon-resistant features as part of all new home construction; improvements in the reliability and accuracy of testing methods to uncover radon in buildings; as well as calling for mandatory testing of radon exposure levels in the workplace, at school, and in daycare facilities.

The effects of radiation depend upon the type of radiation absorbed, the amount or dose received, and the part of the body irradiated. Alpha and beta particles have 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 harmful 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 usually is accompanied by a reduction in WBC production within seventy-two hours, and recovery from a radiation dose is first indicated by an increase in WBC production.

Treatment of radiation exposure or contamination is complicated by the need to prevent contamination or exposure of the attending healthcare professionals. Exposure occurs when the individual has been exposed to a radioactive source, but does not carry radioactive material in or on his or her body or clothing. Contamination occurs when the body or clothing of the individual contains radioactive material. Contamination can be external (clothing or skin) or internal (airways, lungs). Internal contamination is much less common than external contamination, but is also much more difficult to remedy.

Basic treatment steps include protecting the attending healthcare professionals and preventing contamination of the treatment area. When contamination is suspected, a probe attached to a survey Geiger counter is used to identify the location and extent of external contamination. In addition, samples of urine, feces, swabs of the airways, open wounds, and stomach contents may be monitored for radioactivity.

Clothing is removed and quarantined. The body is then decontaminated by washing skin and hair with water and a mild soap until the level of radioactivity is reduced. The used wash water will contain radioactivity and must also be quarantined. Much of the difficulty in treating radiation contamination comes from the need to protect those providing the treatment and to prevent radiation, which can be neither seen nor smelled, from spreading and contaminating new areas.

After the body is free of radiation, care is supportive and depends on symptoms. Long-term follow-up and monitoring for the development of cancers and other health problems is essential

Protection basics for people working in environments where radiation is present consist of shielding and monitoring. Shielding creates a barrier to radiation. The degree of shielding necessary to keep workers safe depends on the type of radiation present and how close they must work to the radiaation source. High-energy radiation has more penetrating power than low-energy radiation and thus greater shielding is necessary. All workers should wear monitoring badges that record their level of radiation exposure so that it does not exceed allowable levels.

The benefits of radiation exposure when used for diagnostic and therapeutic purposes generally outweighs the risks. However, patients should avoid unnecessary diagnostic tests such as x rays and should speak to their physicians and technicians about any concerns they may have about safety.

See also Leukemia ; Radiation ; Ultraviolet radiation .