ultraviolet radiation

ultraviolet radiation,

invisible electromagnetic radiationelectromagnetic radiation,
energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if the motion is changing (accelerated), then the magnetic field varies and in turn produces an electric field.
..... Click the link for more information. between visible violet light and X rays; it ranges in wavelength from about 400 to 4 nanometers and in frequency from about 10¹⁵ to 10¹⁷ hertz. It is a component (less than 5%) of the sun's radiation and is also produced artificially in arc lamps, e.g., in the mercury arc lamp.

The ultraviolet radiation in sunlight is divided into three bands: UVA (320–400 nanometers), which can cause skin damage and may cause melanomatous skin cancerskin cancer,
malignant tumor of the skin. The most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma. Rarer forms include mycosis fungoides (a type of lymphoma) and Kaposi's sarcoma.
..... Click the link for more information. ; UVB (280–320 nanometers), stronger radiation that increases in the summer and is a common cause of sunburnsunburn,
inflammation of the skin caused by actinic rays from the sun or artificial sources. Moderate exposure to ultraviolet radiation is followed by a red blush, but severe exposure may result in blisters, pain, and constitutional symptoms.
..... Click the link for more information. and most common skin cancer; and UVC (below 280 nanometers), the strongest and potentially most harmful form. Much UVB and most UVC radiation is absorbed by the ozone layerozone layer
or ozonosphere,
region of the stratosphere containing relatively high concentrations of ozone, located at altitudes of 12–30 mi (19–48 km) above the earth's surface.
..... Click the link for more information. of the atmosphere before it can reach the earth's surface; the depletion of this layer is increasing the amount of ultraviolet radiation that can pass through it. The radiation that does pass through is largely absorbed by ordinary window glass or impurities in the air (e.g., water, dust, and smoke) or is screened by clothing.

The National Weather Service's daily UV index predicts how long it would take a light-skinned American to get a sunburn if exposed, unprotected, to the noonday sun, given the geographical location and the local weather. It ranges from 1 (about 60 minutes before the skin will burn) to a high of 10 (about 10 minutes before the skin will burn).

A small amount of sunlight is necessary for good health. Vitamin D is produced by the action of ultraviolet radiation on ergosterol, a substance present in the human skin and in some lower organisms (e.g., yeast), and treatment or prevention of ricketsrickets
or rachitis
, bone disease caused by a deficiency of vitamin D or calcium. Essential in regulating calcium and phosphorus absorption by the body, vitamin D can be formed in the skin by ultraviolet rays contained in sunlight; it can also be consumed in such
..... Click the link for more information. often includes exposure of the body to natural or artificial ultraviolet light. The radiation also kills germs; it is widely used to sterilize rooms, exposed body tissues, blood plasma, and vaccines.

Ultraviolet radiation can be detected by the fluorescencefluorescence
, luminescence in which light of a visible color is emitted from a substance under stimulation or excitation by light or other forms of electromagnetic radiation or by certain other means.
..... Click the link for more information. it induces in certain substances. It may also be detected by its photographic and ionizing effects. The long-wavelength, "soft" ultraviolet radiation, lying just outside the visible spectrum, is often referred to as black light; low intensity sources of this radiation are often used in mineral prospecting and in conjunction with bright-colored fluorescent pigments to produce unusual lighting effects.

Bibliography

See L. R. Koller, Ultraviolet Radiation (2d ed. 1965).

Ultraviolet radiation

Electromagnetic radiation in the wavelength range 4–400 nanometers. The ultraviolet region begins at the short wavelength (violet) limit of visibility and extends to the wavelength of long x-rays. It is loosely divided into the near (400–300 nm), far (300–200 nm), and extreme (below 200 nm) ultraviolet regions (see illustration). In the extreme ultraviolet, strong absorption of the radiation by air requires the use of evacuated apparatus; hence this region is called the vacuum ultraviolet. Important phenomena associated with ultraviolet radiation include biological effects and applications, the generation of fluorescence, and chemical analysis through characteristic absorption or fluorescence.

Phenomena associated with ultraviolet radiation

Sources of ultraviolet radiation include the Sun (although much solar ultraviolet radiation is absorbed in the atmosphere); arcs of elements such as carbon, hydrogen, and mercury; and incandescent bodies.

ultraviolet radiation

Electromagnetic radiation lying in the wavelength range beyond the Earth's atmospheric absorption at about 320 nm to the hydrogen Lyman limit at 91.2 nm (see hydrogen spectrum). The gap between the X-ray and UV wavebands is the XUV region. Long-wavelength ultraviolet radiation, i.e. with wavelengths up to 350 nm, near that of light, is often called near-ultraviolet with far-ultraviolet (FUV) being applied to short wavelengths, i.e. 91.2 nm up to about 200 nm.

Ultraviolet Radiation

(also UV radiation, ultraviolet light), invisible electromagnetic radiation that occupies the spectral region between visible light and X rays, which corresponds to the wavelength (λ) range 400-10 nanometers (nm). The ultraviolet region is divided into the near-ultraviolet (400-200 nm) and the far-, or vacuum-, ultraviolet (200-10 nm) regions; the vacuum ultraviolet is so called because the ultraviolet radiation in this region is strongly absorbed by air and is studied with evacuated spectroscopic instruments.

Near-ultraviolet radiation was discovered in 1801 by the German scientist J. Ritter and in 1802 by the British scientist W. Wollaston from its photochemical effect on silver chloride. Vacuum-ultraviolet radiation was observed by the German scientist V. Schumann with an evacuated fluorite-prism spectrograph, which he built between 1885 and 1903, and gelatinless photographic plates. He was able to detect short-wavelength radiation down to 130 nm. The American scientist T. Lyman built the first evacuated spectrograph with a concave diffraction grating and, in 1924, detected ultraviolet radiation with a wavelength as short as 25 nm. By 1927, the entire region between the vacuum ultraviolet and X rays had been studied.

Depending on the nature of the ultraviolet radiation source, an ultraviolet spectrum may be a line, continuous, or band spectrum (seeSPECTRUM, OPTICAL). The ultraviolet radiation from atoms, ions, or light molecules, such as H₂, has a line spectrum. Spectra of heavy molecules are characterized by bands attributable to electronic-vibrational-rotational transitions of the molecules (seeMOLECULAR SPECTRA). A continuous spectrum results from the deceleration or recombination of electrons (see).

Optical properties of matter. The optical properties of substances in the ultraviolet region of the spectrum differ considerably from their optical properties in the visible region. A characteristic difference is a decrease in the transmittance, or an increase in the absorptance, of most solids that are transparent in the visible region. For example, ordinary glass is opaque at λ < 320 nm; at shorter wavelengths, only uviol glass, sapphire, magnesium fluoride, quartz, fluorite, lithium fluoride, and certain other substances are transparent. Among solids, lithium fluoride has the farthest transmission cutoff, namely, 105 nm. For λ < 105 nm, practically no material is transparent.

The most transparent gaseous substances are the inert gases; their transmission cutoff is determined by their ionization’poten-tial. Helium has the shortest-wavelength transmission cutoff, namely, 50.4 nm. Air is practically opaque at λ < 185 nm because of absorption by oxygen.

The reflection coefficient of all materials, including metals, decreases as the wavelength of the radiation decreases. For example, the reflection coefficient of freshly deposited aluminum, which is one of the best materials for mirror coatings in the visible region of the spectrum, decreases sharply at λ < 90 nm (Figure 1). The reflection of light by aluminum is also reduced substantially as a result of surface oxidation. Coatings based on lithium fluoride or magnesium fluoride are used to protect aluminum surfaces from oxidation. In the region λ < 80 nm, several materials, such as gold, platinum, radium, and tungsten, have reflection coefficients of 10-30 percent, but for λ < 40 nm their reflection coefficients are reduced to 1 percent or less.

Figure 1. Plot of the reflection coefficient r of an aluminum layer against wavelength λ: (1) measured Immediately after ultrahigh-vacuum deposition, (2) measured after the layer was kept in the open air for a year

Sources of ultraviolet radiation. The radiation from solids heated to 3000°K contains an appreciable fraction of continuous ultraviolet radiation, whose intensity increases with increasing temperature. More intense ultraviolet radiation is emitted by a gas-discharge plasma. Depending on the discharge conditions and the plasma material, both continuous and line spectra may be emitted. Mercury, hydrogen, xenon, and other types of discharge lamps are manufactured for various uses of ultraviolet radiation. The window or the entire bulb of the lamp is made of a material that is transparent to ultraviolet radiation, most often quartz.

Any high-temperature plasma is a strong ultraviolet source. Examples of such plasmas include spark-discharge plasmas, arc-discharge plasmas, and plasmas produced when intense laser radiation is focused in a gas or on a solid surface. Intense continuous ultraviolet radiation is emitted by electrons accelerated in a synchrotron; such radiation is called synchrotron radiation. Lasers have been developed for the ultraviolet region of the spectrum. The hydrogen laser has the shortest wavelength, namely, 109.8 nm.

Natural sources of ultraviolet radiation include the sun, stars, nebulas, and other celestial objects. Only the long-wavelength portion (λ > 290 nm) of celestial ultraviolet radiation, however, reaches the earth’s surface. Shorter-wavelength ultraviolet radiation is absorbed by ozone, oxygen, and other components of the atmosphere at heights of 30-200 km above the earth’s surface; such absorption plays a large role in atmospheric processes. In addition to the absorption in the earth’s atmosphere, ultraviolet radiation at wavelengths of 91.2-20 nm from stars and other celestial objects is almost totally absorbed by interstellar hydrogen.

Detectors of ultraviolet radiation. Conventional photographic materials are used to detect ultraviolet radiation at λ > 230 nm. Special photographic emulsions containing little gelatin are sensitive to ultraviolet radiation at shorter wavelengths. Photoelectric detectors are used that rely on the ability of ultraviolet radiation to cause ionization and the photoelectric effect; such detectors include photodiodes, ionization chambers, scintillation counters, and photomultipliers.

A special type of photomultiplier, called the channel multiplier, has also been developed; this device is used to construct microchannel plates. Each stage in a microchannel plate is a channel multiplier with a maximum of 10 micrometers. MicroChannel plates make it possible to obtain a photoelectric display of ultraviolet radiation and to combine the advantages of the photographic and photoelectric methods of radiation detection.

Various luminescent substances that convert ultraviolet radiation to visible light are also used in the study of ultraviolet radiation. The instruments that make ultraviolet images visible are based on luminescence.

Uses of ultraviolet radiation. Ultraviolet emission, absorption, and reflectance spectra are studied in order to determine the electronic structure of atoms, ions, molecules, and solids. The ultraviolet spectra of the sun, stars, and other celestial objects carry information on the physical processes that occur in hot regions of the objects (see and VACUUM SPECTROSCOPY). Photoelectron spectroscopy is based on the photoelectric effect induced by ultraviolet radiation. Ultraviolet radiation can break the chemical bonds in molecules; as a result of this effect, such chemical reactions as oxidation, reduction, decomposition, and polymerization can occur.

Luminescence caused by ultraviolet radiation underlies the operation of fluorescent lamps and luminous paints and is made use of in luminescence analysis and in fluorescent pénétrant inspection. Ultraviolet radiation is used in criminalistics to identify dyes and to establish the authenticity of documents. In art studies, ultraviolet radiation makes it possible to detect invisible signs of restoration in paintings. The capability of many substances for selective absorption of ultraviolet radiation is used in the detection of air pollution and in ultraviolet microscopy.

REFERENCES

Meyer, A., and E. Seitz. Ul’trafioletovoe izluchenie. Moscow, 1952. (Translated from German.)
Lazarev, D. N. Ul’trafioletovaia radiatsüa i ee primenenie. Leningrad-Moscow, 1950.
Samson, J. A. R. Techniques of Vacuum Ultraviolet Spectroscopy. New York-London-Sydney [1967].
Zaidel’, A. N., and E. Ia. Shreider. Spektroskopiia vakuumnogo ul’trafioleta. Moscow, 1967.
Stoliarov, K. P. Khimicheskii analiz v ul’trafioletovykh luchakh. Moscow-Leningrad, 1965.
Baker, A., and D. Betteridge. Fotoelektronnaiaspektroskopiia. Moscow, 1975. (Translated from English.) A. N. RIABTSEV
Biological effects of ultraviolet radiation. The effects of ultraviolet radiation on living organisms are associated with the absorption of the radiation by the outer layers of plant tissues or of human and animal skin. Chemical changes in biopolymer molecules are the basis for the biological effects of ultraviolet radiation. Such changes result both from the direct absorption of photons by the molecules and, to a lesser extent, from the radicals of water and other compounds of low molecular weight that form during irradiation.

Figure 2. Action spectra for the effects of ultraviolet radiation on some living things: (a) the occurrence of mutations in corn pollen (circles) and the absorption spectrum of nucleic acids (solid line), (b) the immobilization of paramecia (circles) and the absorption spectrum of albumin (solid line)
In man and animals, small doses of ultraviolet radiation have a beneficial effect: the development of D vitamins (seeCALCIFEROLS) is facilitated, and the biological immunity of the organism is enhanced. The typical reaction of the skin to ultraviolet radiation is a specific reddening, called erythema, which usually develops into protective pigmentation (suntan). Ultraviolet radiation with λ = 296.7 nm and λ = 253.7 nm has the greatest erythemal effect. Large doses of ultraviolet radiation can cause eye injury (photo-ophthalmia) and sunburn. In certain cases, frequent and excessive doses can have a carcinogenic effect on the skin.
In plants, ultraviolet radiation alters the activity of enzymes and hormones and affects the formation of pigments, the rate of photosynthesis, and photoperiodism reactions. It has not been determined whether small doses of ultraviolet radiation are useful, let alone necessary, for the germination of seeds, the development of sprouts, and the normal vital activities of higher plants. Large doses of ultraviolet radiation are undoubtedly detrimental to plants, as is evidenced by the protective devices that exist in plants, such as the accumulation of certain pigments and the cellular mechanisms for recovery from injuries.
In microorganisms and in cultured cells of higher animals and plants, ultraviolet radiation has lethal and mutagenic effects; radiation with λ in the range 280-240 nm is the most effective in this respect. The spectrum of the lethal and mutagenic action of ultraviolet radiation usually coincides roughly with the absorption spectrum (Figure 2,a) of the nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). In some cases, the action spectrum is similar to the absorption spectrum of proteins (Figure 2,b). Chemical changes in DNA apparently play a major role in the effects of ultraviolet radiation on cells; when ultraviolet photons are absorbed, the pyrimidine bases (mainly thymine) of which DNA is composed form dimers that inhibit the normal replication of DNA when a cell is ready to divide. This inhibition can lead to the death of cells or to mutations, that is, changes in the hereditary properties of cells. Injury to biological membranes and the disruption of the formation of various components of membranes and cell walls are also definite factors in the lethal effect of ultraviolet radiation on cells.
Most living cells can recover from injuries caused by ultraviolet radiation because they contain repair systems. The ability to recover from such injuries probably developed in the early stages of evolution and played an important role in the survival of primitive organisms exposed to intense ultraviolet radiation from the sun.
Living things differ greatly in their sensitivity to ultraviolet radiation. For example, the dose of ultraviolet radiation that kills 90 percent of the cells is equal to 10,100, or 800 ergs/mm² for different strains of the bacillus Escherichia coli but is equal to 7,000 ergs/mm² for the bacterium Micrococcus radiodurans (Figure 3,a and b). The sensitivity of cells to ultraviolet radiation also depends to a large extent on their physiological state and on culture conditions (for example, the temperature and composition of the culture medium) before and after irradiation. The mutations of certain genes greatly affect the sensitivity of cells to ultraviolet radiation. About twenty genes in bacteria and yeasts are known to have mutations that make the organisms more sensitive to ultraviolet radiation. In a number of cases, these genes are responsible for a cell’s recovery from radiation damage. Mutations of other genes disrupt the synthesis of proteins and the building of cell membranes, thereby increasing the radiosensitivity of the nongenetic components of a cell. Mutations that increase the sensitivity to ultraviolet radiation are also known for higher organisms, including man. For example, the hereditary disease xeroderma pigmentosum is caused by mutations of the genes that regulate dark repair.

Figure 3. Plots of the survival rate of various bacteria against ultraviolet radiation dose: (a) E. coli, wavelength of 253.7 nm; (1), (2) mutant strains, (3) wild type, (b) M. radiodurans, wavelength of 265.2 nm.
The genetic consequences of exposing the pollen of higher plants, the cells of plants and animals, and microorganisms to ultraviolet radiation include a higher incidence of gene, chromosome, and plasmid mutations. The frequency of mutation for individual genes exposed to high doses of ultraviolet radiation may increase by a factor of several thousand in comparison with the natural level and may reach several percent. Unlike the genetic effects of ionizing radiation, mutations of genes exposed to ultraviolet radiation occur relatively more often than mutations of chromosomes. As a result of its strong mutagenic effect, ultraviolet radiation is widely employed both in genetic research and in the breeding of plants and of microorganisms used in industry as producers of antibiotics, amino acids, vitamins, and protein biomass. The genetic effects of ultraviolet radiation may have played a significant role in the evolution of living organisms. The use of ultraviolet radiation in medicine is discussed in PHOTOTHERAPY.

REFERENCES

Samoilova, K. A. Deistvie ul’trafioletovoi radiatsii na kletku. Leningrad, 1967.
Dubrov, A. P. Genelicheskie i fiziologicheskie effekty deistviia ul’trafioletovoi radiatsii na vysshie rasteniia. Moscow, 1968.
Galanin, N. F. Luchistaia energiia i ee gigienicheskoe znachenie. Leningrad, 1969.
Smith, K., and P. Hanawalt. Molekuliarnaia fotobiologiia. Moscow, 1972. (Translated from English.)
Shul’gin, I. A. Rastenie isolntse. Leningrad, 1973.
Miasnik, M. N. Geneticheskii kontrol’ radiochuvstvitel’nosti bakterii. Moscow, 1974.

V. I. KOROGODIN

ultraviolet radiation

[¦əl·trə′vī·lət ‚rād·ē′ā·shən] (electromagnetism) Electromagnetic radiation in the wavelength range 4-400 nanometers; this range begins at the short-wavelength limit of visible light and overlaps the wavelengths of long x-rays (some scientists place the lower limit at higher values, up to 40 nanometers). Also known as ultraviolet light.

ultraviolet radiation

Electromagnetic radiation at wavelengths immediately below the visible spectrum, i.e., within the wavelength range 10 to 380 nm. May be classified as: far ultraviolet, 10 to 280 nm; middle ultraviolet, 280 to 315 nm; near ultraviolet, 315 to 380 nm. Also may be classified as: ozone-producing, 180 to 220 nm; germicidal, 220 to 300 nm; erythemal, 280 to 320 nm; black light, 320 to 400 nm. In either method of classification, there are no sharp demarcations between the wavelength bands.

ultraviolet radiation

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 radiation" >electromagnetic radiation, which consists of wave motion of electric and magnetic fields. The theory" >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 radiation" >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 cortexprimary 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 radiation" >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

ultraviolet radiation

ultraviolet radiation

ultraviolet radiation

ultraviolet radiation,

Bibliography

Ultraviolet radiation

ultraviolet radiation

Ultraviolet Radiation

REFERENCES

REFERENCES

ultraviolet radiation

ultraviolet radiation

ultraviolet radiation

radiation

ultraviolet light

ul·tra·vi·o·let ra·di·a·tion

ultraviolet light or ultraviolet radiation (UV)

Ultraviolet radiation (UV)

Patient discussion about ultraviolet radiation

ultraviolet radiation

Synonyms for ultraviolet radiation

noun radiation lying in the ultraviolet range

Synonyms

Related Words