ultraviolet radiation


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radiation

 [ra″de-a´shun]
1. a proceeding outward from a common center.
2. a structure made up of parts that go outward from a center, especially a tract of the central nervous system made up of fibers that go out in different dfirections.
3. energy carried by waves or a stream of particles. One type is electromagnetic radiation, which consists of wave motion of electric and magnetic fields. The quantum theory is based on the fact that electromagnetic waves consist of discrete “packets” of electromagnetic radiation, called photons, which have neither mass nor charge and have an energy inversely proportional to the wavelength of the wave. In order of increasing photon energy and decreasing wavelength, the electromagnetic spectrum is divided into radio waves, infrared light, visible light, ultraviolet light, and x-rays. 

Another type is the radiation emitted by radioactive materials. alpha particles are high-energy helium-4 nuclei consisting of two protons and two neutrons, emitted by radioisotopes of heavy elements such as uranium. beta particles are high-energy electrons emitted by radioisotopes of lighter elements. gamma rays are high-energy photons emitted along with alpha and beta particles and also emitted alone by metastable radionuclides, such as technetium-99m. Gamma rays have energies in the x-ray region of the spectrum and differ from x-rays only in that they are produced by radioactive decay rather than by x-ray machines.

Radiation with enough energy to knock electrons out of atoms and produce ions is called ionizing radiation and includes alpha particles, beta particles, x-rays, and gamma rays. This kind of radiation can produce tissue damage directly by striking a vital molecule, such as DNA, or indirectly by striking a water molecule and producing highly reactive free radicals that chemically attack vital molecules. The effects of radiation can kill cells, make them unable to reproduce, or cause nonlethal mutations, producing cancer cells or birth defects in offspring. The radiosensitivity of normal tissues or cancer cells increases with their rate of cell division and decreases with their rate of cell specialization. Highly radiosensitive cells include lymphocytes, bone marrow hematopoietic cells, germ cells, and intestinal epithelial cells. Radiosensitive cancers include leukemias and lymphomas, seminoma, dysgerminoma, granulosa cell carcinoma, adenocarcinoma of the gastric epithelium, and squamous cell carcinoma of skin, mouth, nose and throat, cervix, and bladder.

The application of radiation, whether by x-ray or radioactive substances, for treatment of various illnesses is called radiation therapy or radiotherapy.

Three types of units are used to measure ionizing radiation. The roentgen (R) is a unit of exposure dose applicable only to x-rays and gamma rays. It is the amount of radiation that produces 2.58 × 10−4 coulomb of positive and negative ions passing through 1 kilogram of dry air. The rad is a unit of absorbed dose equal to 100 ergs of energy absorbed per 1 g of absorbing material; the absorbed dose depends both on the type of radiation and on the material in which it is absorbed. The rem is a unit of absorbed dose equivalent that produces the same biologic effect as 1 rad of high-energy x-rays. For beta and gamma radiation, 1 rem is approximately equal to 1 rad; for alpha radiation, 1 rad is approximately 20 rem.

Previously, doses administered in radiation therapy were commonly specified as measured exposure doses in roentgens. The current practice is to specify the absorbed dose in the tissue or organ of interest in rads. Many personnel monitoring devices read out in rems. Eventually, the rad and rem may be replaced by the new SI units, the gray and sievert; 1 gray equals 100 rad, and 1 sievert equals 100 rem.
Radiation Hazards. Harmful effects of radiation include serious disturbances of bone marrow and other blood-forming organs, burns, and sterility. There may be permanent damage to genes, which results in genetic mutations. The mutations can be transmitted to future generations. Radiation also may produce harmful effects on the embryo or fetus, bringing about fetal death or malformations. Long-term studies of groups of persons exposed to radiation have shown that radiation acts as a carcinogen; that is, it can produce cancer, especially leukemia. It also may predispose persons to the development of cataracts. 

Exposure to large doses of radiation over a short period of time produces a group of symptoms known as the acute radiation syndrome. These symptoms include general malaise, nausea, and vomiting, followed by a period of remission of symptoms. Later, the patient develops more severe symptoms such as fever, hemorrhage, fluid loss, anemia, and central nervous system involvement. The symptoms then gradually subside or become more severe, and may lead to death.
Radiation Protection. In order to avoid the radiation hazards mentioned above, one must be aware of the three basic principles of time, distance, and shielding involved in protection from radiation. Obviously, the longer one stays near a source of radiation the greater will be the exposure. The same is true of proximity to the source; the closer one gets to a source of radiation the greater the exposure. 

Shielding is of special importance when time and distance cannot be completely utilized as safety factors. In such instances lead, which is an extremely dense material, is used as a protective device. The walls of diagnostic x-ray rooms are lined with lead, and lead containers are used for radium, cobalt-60, and other radioactive materials used in radiotherapy.

Monitoring devices such as the film badge, thermoluminescent dosimeter, or pocket monitor are worn by persons working near sources of radiation. These devices contain special detectors that are sensitive to radiation and thus serve as guides to the amount of radiation to which a person has been exposed. For monitoring large areas in which radiation hazards may pose a problem, survey meters such as the Geiger counter may be used. The survey meter also is useful in finding sources of radiation such as a radium implant, which might be lost.

Sensible use of these protective and monitoring devices can greatly reduce unnecessary exposure to radiation and allow for full realization of the many benefits of radiation.
Penetrating capacity of different types of radiation. From Ignatavicius and Workman, 2002.
Radiation is emitted by radioactive material. Radiation quantity is measured in roentgens, rads, or rems, depending on precise use. From Bushong, 2001.
corpuscular radiation particles emitted in nuclear disintegration, including alpha and beta particles, protons, neutrons, positrons, and deuterons.
electromagnetic radiation energy, unassociated with matter, that is transmitted through space by means of waves (electromagnetic waves) traveling in all instances at 3×1010 cm or 186,284 miles per second, but ranging in length from 1011 cm (electrical waves) to 10−12 cm (cosmic rays) and including radio waves, infrared, visible light and ultraviolet, x-rays, and gamma rays.
extrafocal radiation radiation that arises from a source other than the focal spot of the x-ray tube.
infrared radiation the portion of the spectrum of electromagnetic radiation of wavelengths between 0.75 and 1000 μm; see also infrared.
interstitial radiation energy emitted by radium, radon, or some other radiopharmaceutical inserted directly into the tissue; see also radiation therapy.
ionizing radiation corpuscular or electromagnetic radiation that is capable of producing ions, directly or indirectly, in its passage through matter. See also radiation.
optic radiation either of two large fan-shaped fiber tracts in the brain extending from the lateral geniculate body on either side to the striate cortex
primary radiation that coming directly from a source, such as a radioactive substance or an x-ray tube, without interactions with matter.
pyramidal radiation fibers extending from the pyramidal tract to the cortex.
scatter radiation (secondary radiation) that generated by the interaction of primary radiation with matter. See illustration.
Three types of radiation—the useful beam, leakage radiation, and scatter radiation. From Bushong, 2001.
striothalamic radiation a fiber system joining the thalamus and the hypothalamic region.
tegmental radiation fibers radiating laterally from the nucleus ruber.
thalamic r's fibers streaming out through the lateral surface of the thalamus, through the internal capsule to the cerebral cortex.
ultraviolet radiation the portion of the spectrum of electromagnetic radiation of wavelengths between 0.39 and 0.18 μm; see also ultraviolet rays.

ultraviolet light

The segment of the electromagnetic spectrum between 200 and 400 nm, including photons emitted during electronic transition states. UV-C (200–290 nm) is damaging to DNA and amino acids, but is blocked in the stratospheric ozone layer; UV-B (290–320 nm) is partially blocked by the ozone layer; UV-A (320–400 nm) is the least dangerous, but may still be hazardous with photosensitising medications (e.g., tetracyclines, thiazides), and in patients with lupus erythematosus and light sensitivity disorders (e.g., porphyria). UV-A suppresses delayed cutaneous hypersensitivity, causes photoageing and reduces serum carotenoids; the accelerating depletion of the stratospheric ozone is implicated in the increased incidence of cataract, and melanomas.

UV light may also damage the less sensitive purines, causing spontaneous depurination, leaving a “naked” deoxyribose residue in the DNA (apurinic sites). Repair of UV-light-induced DNA damage is defective in chromosomal breakage syndromes (e.g., xeroderma pigmentosa and Bloom syndrome). The mutational effect of UV light is not due to direct DNA damage, but rather occurs during the error-prone process of DNA repair.

ul·tra·vi·o·let ra·di·a·tion

(ŭl'tră-vī'ŏ-lĕt rā'dē-ā'shŭn)
A wavelength of electromagnetic radiation that is shorter than that of visible light.

ultraviolet light or ultraviolet radiation (UV)

a type of electromagnetic radiation beyond the wavelength of visible violet light, ranging from 18,000 to 33,000 nm (see ELECTROMAGNETIC SPECTRUM). UV light is not an ionizing radiation like X-RAYS and can only penetrate a few cells. However, it is used as a powerful MUTAGEN of microorganisms to cause the formation of thymine DIMERS in DNA, and can be harmful to the human RETINA. Some organisms can detect UV light (see ENTOMOPHILY). UV is a common cause of skin cancers; see MELANOMA.

Ultraviolet radiation (UV)

Invisible light rays that may be responsible for sunburns, skin cancers, and cataract formation.
Mentioned in: Cataracts

Patient discussion about ultraviolet radiation

Q. what does a sun block cream do? and what are a UV rays?

A. It blocks out harmful Ultra violet rays from the skin as the previous entries have related; however it can also block your ability to produce vitamin D. If you live in a northerly area or one that receives limited sunlight, its recommended to get at least 15 minutes of sun a day (this is probably best done with minimal sunblock) and according to personnal sun sensitivity. Another thing to keep in mind is that sunblock works best if applied 20 minutes before sun exposure.

More discussions about ultraviolet radiation
References in periodicals archive ?
Ultraviolet radiation and skin cancer: molecular mechanisms.
However, earth edge energy at ultraviolet radiation, no matter at day or at night, is adapted to the detection of ultraviolet.
In addition to the use of umbrellas, doctors recommend people use sun creams, hats and clothing when at the beach to guard against ultraviolet radiation, and avoid hours when the sun is at its highest.
The vast majority of skin cancers are associated with ultraviolet radiation exposure.
The Commission's Scientific Committee on Consumer Products (SCCP) has concluded that "the use of ultraviolet radiation devices clearly increases the risk of malignant melanoma of the skin", or in layman's terms, skin cancer.
The inactivating effect of monochromatic ultraviolet radiation on influenza virus.
The main cause of skin cancer is exposure to ultraviolet radiation - and most exposure comes from sunlight.
Ultraviolet radiation at the biocidal wavelength of 254 nanometers eliminates bacteria from the system.
Sandbag materials differ in their resistance to the elements--especially ultraviolet radiation. In response to reports that sandbag fortifications have failed under the intense sunlight in Iraq, the United States Army Engineer Research and Development Center (ERDC) conducted a study to identify which materials maintain tensile strength the longest under ultraviolet radiation exposure.
WITH NEARLY 3 MILLION new cases of skin cancer diagnosed annually worldwide, avoiding too much ultraviolet radiation becomes critical.
Joshua Bomser, from Ohio State University said: "Along with the many environmental, lifestyle and genetic risk factors associated with cataracts, exposure to ultraviolet radiation from sunlight and oxidative stress appear to be the most relevant in this disease.
The book provides pertinent information on travelers' medical kits, water disinfection, and noninfectious health risks such as high altitude, arctic travel, diving, jet lag, and ultraviolet radiation. New for this edition are informative chapters on deep vein thrombosis and pulmonary embolism and in-flight accidents.

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