X-rays and Radiation        
There are many types of radiation that people can feel or see, including heat and light, but there are other kinds of radiation that human senses cannot detect. We constantly receive such invisible radiation from the sky, the ground, the air, and even our food and drink. Potassium-40 and other radioactive isotopes found in air, water and soil are incorporated into food, then into the body's own tissues.


"Ionizing" radiation passes through matter and can cause some of its atoms to become electrically charged, or ionized. Ionizing radiation comes in several different forms:

Alpha particles - are positively charged particles. They are easily stopped by paper or skin, and are only hazardous if alpha-emitting materials are swallowed or breathed into the body.
Beta particles - are electrons and have a greater penetrating power than alpha particles, but can be stopped by thin layers of water, glass or metal.
Gamma and X-rays - are electromagnetic radiations similar to light and radio waves but with shorter wavelengths.
Neutrons - are particles with no charge; they are neutral, and because of this they can penetrate many materials very easily. They do not produce ionization directly, but their interaction with atoms can give rise to alpha, beta, gamma or X-rays, which produce ionization.
When high-speed electrons hit metals and other solids, electrons are stopped and release energy in the form of an electromagnetic wave.

Wilhelm Roentgen first observed this in 1895, and considered it a mysterious ray, which he called an X-ray.

Such "ionizing" radiation has been put to many uses: doctors use X-rays to diagnose disease or injury, factories use radiation to check welds in machine components and find contaminants in pre-packaged products, and gamma rays are used to sterilize medical equipment for safe use. There are hundreds of other beneficial uses of man-made radiation, including nuclear medicine pharmaceuticals, television sets and nuclear power plants. Its effect on humans is no different from that of natural background radiation. Unlike nature's radiation, however, the use and handling of man-made radiation is strictly controlled and regulated. Most of the public's exposure to man-made radiation comes from medical X-rays, as well as other medical diagnostic and treatment procedures using radioactive materials.

Our standard of living and way of life are maintained in part through the many uses of man-made radiation. Man-made radioactive radioisotopes are used in basic scientific research, energy production, medicine, manufacturing, minerals exploration, agriculture and consumer products.

Radioactive materials are integral to research in nearly all fields of modern science. Medical researchers, for example, use radioisotopes as tracers to help find cures for major diseases.

Nuclear power plants generate one-sixth of the world's electricity, without emitting greenhouse gases or other pollutants.

About 10 million nuclear medicine procedures are performed in the United States every year, prolonging and improving the quality of thousands of lives. Today, approximately 500,000 cancer patients in the United States receive radiation treatment at some point in their therapy. Radioisotopes and X-rays also are used to diagnose and treat scores of other diseases.

Radiation is used to sterilize hospital items, thereby helping to prevent the spread of diseases. The process does not make the items radioactive. Because of its penetrating power, radiation is particularly suitable for sterilizing items such as sutures, syringes, catheters and hospital clothing that are packed in hermetically sealed packages prior to sterilization. Heat cannot be used to sterilize these items because it would destroy the materials.

Man-made radioactive materials, radioisotopes, are used by industry to extract minerals and to improve the quality of manufactured goods in thousands of industrial plants throughout the world. Examples include the use of radioisotopes to help explore for oil and natural gas; for nondestructive testing of pipes and welds; to control thickness and moisture content during the manufacturing of paper and steel; to measure the density of road surfaces; and to "cold sterilize" plastics, pharmaceuticals, cosmetics and other products that are too heat-sensitive to be sterilized in other ways.

Neutron activation analysis is used for chemical analyses in criminology. The radioactive isotope americium-241 is used in some smoke detectors. The presence of smoke in the detector impedes the flow of radiation from the radioactive source, setting off the alarm.

Radiation has been used to breed new seed varieties with higher yields, such as the "miracle" rice that has greatly expanded rice production in Asia.

Radioisotope thermoelectric generators (RTGs) are used to provide power for unmanned spacecraft. RTGs use the natural decay of plutonium dioxide to produce heat, which is transformed into electrical power through thermoelectric devices. A typical modern RTG produces about 300 watts and will operate unattended for many years. RTGs have been used to provide power for 24 U.S. space missions, with an unparalleled safety record.

Nuclear reactors are used to power both surface ships and submarines. Nuclear propulsion gives submarines two major advantages, speed and underwater range without surfacing. The modern U.S. submarine, for example, can cruise up to one million miles, or more than 25 years, without needing to refuel. Modern nuclear-powered surface ships can operate continuously at high speeds for extended periods without the need for support ships.


Background Radiation

In our daily life, we are exposed to various types of naturally occurring radiation from cosmic rays, from radioactive substances in the earth, and from naturally occurring radiation in our bodies. This is commonly referred to as background radiation.

Everyone is exposed to radiation, and for most people nature is the largest source of exposure.

Cosmic radiation comes through the earth's atmosphere, some from the sun and energy sources in our galaxy or outside it. Those from the sun are more intense during solar flares but the others are fairly constant in number. However, the density is affected by the earth's magnetic field, which makes it greater nearer the poles than the equator. The radiation dose people receive increases therefore with latitude. In addition, the earth's atmosphere is a partial shield to the radiation. As one goes higher there is a lower shielding effect and the dose increases as the altitude increases. Living at high elevations increases the amount of exposure. Buildings and the fuselages of aircraft provide little protection. According to the Federal Aviation Administration, at 37,000 feet, air travelers are exposed to as much as 265 times the radiation dose they receive on the ground. A four hour aircraft flight exposes you to the same radiation dose (from cosmic rays) as a chest X-ray.

The earth's crust is made up of materials that are naturally radioactive. Uranium, for instance, is dispersed throughout rocks and soil, mostly at very low concentrations. So are thorium and potassium-40. They nearly all emit gamma rays, which irradiate the whole body more or less uniformly. Since building materials are extracted from the earth, they can be slightly radioactive, and people are irradiated indoors as well as out of doors. The materials that compose a house or workplace can also be a major factor in radiation exposures of external origin. Some construction materials can serve as shields against radiation; others are sources of radiation. For example, clay (bricks) and concrete are often relatively high in radioactive substances of natural origin. Consequently, the dose rates inside buildings made of these materials generally exceed those outside. In contrast, wood contains virtually no naturally occurring radioactive substances that contribute to radiation exposures of external origin. Thus, the dose rates inside wooden buildings are generally lower than those outside. The radiation doses vary according to the rocks and soils of the area and the building materials in use. There is no evidence of any increase in cancer among people living in areas where natural, background radiation is several times higher than average such as Han (China), Kerala (India) or Araxa-Tapira (Brazil).

Radon is a naturally radioactive gas that comes from the uranium that is widespread in the earth's crust. It is emitted from rocks or soil at the earth's surface and disperses in the atmosphere unless it enters a building, in which the concentration can build up.

Since radioactive materials occur everywhere in nature it is inevitable that they get into drinking water and food. Some foods, for example shellfish and Brazil nuts, concentrate radioactive materials so that, even when there is no artificial radioactivity, people who consume large quantities can receive a radiation dose significantly above average. Potassium is a biochemically essential nutrient found in widely diverse foods. Because the radiation from the potassium isotope is very penetrating, it can be a source of exposure to persons nearby.