Radiation Injuries - Description

The word radiation comes from a Latin term that means "ray of light." It is used in a general sense to cover all forms of energy that travel through space from one place to another as "rays." Some forms of radiation are relatively harmless, like radio waves. Some forms of radiation carry a tremendous amount of energy and cause damage when they come into contact with other materials.

These high energy forms of radiation cause damage to substances by tearing apart the atoms and molecules that make up the substances. This may cause materials to undergo harmful changes. For example, an X ray that passes through water can tear the molecules of water apart. An X ray that passes through a living cell can also damage the cell by tearing apart the chemicals that make up the cell. The cell may be badly injured or killed.

Any form of radiation that can tear atoms and molecules apart is called ionizing radiation (IR). Damage to the body caused by IR is known as radiation injury. Ionizing radiation can come in the form electromagnetic waves or subatomic particles.

Electromagnetic Waves

Radio and television signals, radar, heat, infrared and ultraviolet radiation, sunlight, starlight, gamma rays, cosmic rays, and X rays are all forms of electromagnetic radiation (ER). All forms of electromagnetic radiation travel in the form of waves at the speed of light (182,282 miles per second, 299,727 kilometers per second). Because ER travels in waves, its energy can be expressed in terms of wavelengths. Types of ER differ with regard to wavelength. The higher the energy wave, the shorter its wavelength. Types of ER also differ from one another with regard to their frequency. The frequency of a wave is the rate at which it vibrates in space.

X rays, gamma rays, and cosmic rays all have very high frequencies and short wavelengths. They vibrate very rapidly—many billions of times per second—in space. Radio and television signals and radar all have very low frequencies and long wavelengths. They vibrate quite slowly in space.

Waves that vibrate rapidly (have high frequencies) are carry more energy and can cause damage to substances by tearing apart the atoms and molecules that make up the substances.

Bone marrow:
Tissue found in the center of bones from which all types of blood cells are formed.
Electromagnetic radiation (ER):
Radiation that travels as waves at the speed of light.
The rate at which a wave vibrates in space.
Gray (Gy):
A unit used to measure the amount of damage done to tissue by ionizing radiation.
Ionizing radiation (IR):
Any form of radiation that can break apart atoms and molecules and cause damage to materials.
An older unit used to measure the amount of damage done to tissue by ionizing radiation, now replaced by the gray.
Energy transmitted in the form of electromagnetic waves or subatomic particles.
Radioactive element:
An element that gives off some form of radiation and breaks down into a different element or a different form of the same element.
An older unit used to measure the amount of damage done to tissue by ionizing radiation, now replaced by the sievert.
Sievert (Sv):
A unit used to measure the amount of damage done to tissue by ionizing radiation.

Particulate Radiation

Radioactive elements also give off forms of radiation similar to electro-magnetic radiation, but it is given off in sprays of subatomic particles. These particles may be produced intentionally in machines know as particle accelerators (atom-smashers) or they may be given off spontaneously by naturally occurring radioactive materials such as uranium 235 and radium 226. These forms of radiation can also cause damage to atoms and molecules.

Measuring Damage

There are two units used to measure the damage done to tissue by ionizing radiation. Those units were once called the rad and the rem. They have now been given new names, the gray (Gy) and the sievert (Sv). These units are very similar to, but not exactly the same as, each other.

The damage IR causes to a body can range from very mild to very severe. The damage depends on a number of factors, including the kind of radiation, how close the person is to the source of radiation, and how long the person was exposed to the radiation. In mild cases, a radiation injury may be no more serious than a mild sunburn. In the most serious cases, radiation injury can cause death within a matter of hours.

Humans are exposed to ionizing radiation from a variety of sources. These sources fall into four general categories: natural, intentional, accidental, and therapeutic. Natural sources include sunlight and cosmic radiation. Sunlight includes not only visible light, which has relatively few health effects, and radiation of higher frequency, such as ultraviolet radiation. Just stepping outdoors exposes a person to IR in sunlight.

Cosmic rays are similar to sunlight in that they are always present around us. They are not visible, but they do contain ionizing radiation. Exposure to natural sources of IR account for a very small fraction of radiation injuries.

Intentional exposure to IR is rare. It occurs when nuclear weapons (hydrogen and atomic bombs) are used as weapons of war. This has occurred only twice in history, when the United States dropped atomic bombs on Hiroshima and Nagasaki, Japan, at the end of World War II. Many thousands of people were killed or injured by these attacks. They are the only people ever to have been injured by intentional exposure to IR.

Accidental exposure occurs when a person is exposed to IR by mistake. For example, radioactive elements are sometimes spilled in a research laboratory. Workers in the lab may be exposed to the IR from those elements.

Accidental exposure to IR has caused a number of radiation injuries and deaths. Between 1945 and 1987, there were 285 nuclear reactor accidents worldwide. More than fifteen hundred people were injured and sixty-four were killed in these accidents.

Therapeutic exposure to IR occurs during various medical procedures. Radioactive elements and ionizing radiation have many valuable applications in diagnosing and treating disorders. But those treatments can have harmful as well as beneficial effects on patients. The rate of radiation injuries due to this cause probably cannot be measured. Many people who may have been injured by a radiation treatment probably died of the condition for which they were being treated.

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