X-rays

X-rays, or roentgen rays, are electromagnetic waves in which periodically variable electric and magnetic fields are perpendicular to each other and to the direction of propagation. Thus they are identical in nature with visible light and all the other types of radiation that constitute the electromagnetic spectrum. In general, x-rays are generated as the result of energy transitions of atomic electrons caused by the bombardment of a material of high atomic weight by high-energy electrons. See Electromagnetic radiation

Following W. R. Röntgen's discovery of “a new kind of ray” in 1895, other scientists found the essential experimental conditions to prove that x-rays can be polarized, diffracted by crystals, refracted in prisms and in crystals, reflected by mirrors, and diffracted by ruled gratings. See X-ray optics

The range of x-rays in the electromagnetic spectrum, as excited in x-ray tubes by the bombardment of anode targets by cathode electrons under a high accelerating potential, overlaps the ultraviolet range on the order of 100 nanometers on the long-wavelength side, and the shortest-wavelength limit moves downward as voltages increase. An accelerating potential of 10⁹ volts, now readily generated, produces a wavelength of 10^-15 m (10^-6 nm). An average wavelength used in research is 0.1 nm, or about 1/6000 the wavelength of yellow light. See X-ray tube

In diffraction, refraction, polarization, and interference phenomena, x-rays, together with all other related radiations, appear to act as waves. In other phenomena—such as the appearance of sharp spectral lines, a definite short-wavelength limit of the continuous “white” spectrum, the shift in wavelength of x-rays scattered by electrons in atoms (Compton effect), and the photoelectric effect—the energy seems to be propagated and transferred in quanta, called photons. See Compton effect, Electron diffraction, Neutron diffraction, Photoemission, Quantum mechanics

Important uses have been found for x-rays in many fields of scientific endeavor, for example, roentgen spectrometry and roentgen diffractometry. Extensive tables of the wavelengths of x-ray emission lines in series (K, L, M, and so on) and so-called absorption edges, characteristic of the chemical elements, afford the necessary information for chemical analyses, exactly as in the case of optical emission spectra and for derivation of theories of atomic structure to account for the origin of spectra. See X-ray crystallography, X-ray diffraction, X-ray powder methods

X-rays

High-energy electromagnetic radiation lying between gamma rays and ultraviolet radiation in the electromagnetic spectrum. The XUV region bridges the gap between the X-ray and ultraviolet bands. X-rays, unlike light and radio waves, are usually considered in terms of photon energy, h ν, where ν is the frequency of the radiation and h is the Planck constant. X-ray energies range from about 100 electronvolts (eV) up to about 100 000 eV, corresponding to a wavelength range of about 12 nanometers (nm) to about 0.012 nm. Low-energy X-rays are sometimes called soft X-rays to distinguish them from high-energy or hard X-rays. In astronomy, thermal X-rays are produced from very high temperature gas (˜10⁶–10⁸ K), with nonthermal X-rays arising from the interaction of high-energy electrons with a magnetic field (synchrotron emission) or with low-energy photons (inverse Compton emission – see Compton scattering). See also nonthermal emission; thermal emission.

x-rays

[′eks ‚rāz] (physics) A penetrating electromagnetic radiation, usually generated by accelerating electrons to high velocity and suddenly stopping them by collision with a solid body, or by inner-shell transitions of atoms with atomic number greater than 10; their wavelengths range from about 10^-5 angstrom to 10³ angstroms, the average wavelength used in research being about 1 angstrom. Also known as roentgen rays; x-radiation.

x-rays

[eks´rāz] high-energy radiation" >electromagnetic radiation produced by the collision of a beam of electrons with a metal target in an tube" >x-ray tube; the penetrability and hardness of the x-rays increase with the voltage applied to the tube, which controls the speed with which the electrons strike the target. Called also roentgen rays.

For diagnostic radiography, tube voltages in the range 80 to 120 kilovolts peak (kVp) are normally used. For radiation therapy, voltages in the 1 to 2 megavolt range are used for most treatment. Accelerating electrons to speeds high enough to produce megavoltage x-rays requires a linear accelerator (lineac). Kilovoltage lower than 80 kVp is often used for the extremities, 25 to 30 kVp is used for mammography, and up to 150 kVp can be used for chest imaging.
The x-ray exposure is proportional to the tube current (milliamperage) and also to the exposure time. In diagnostic radiography, the tube voltage and current and exposure time are selected to produce a high-quality radiograph with the correct contrast and film density. In radiation therapy, these exposure factors are selected to deliver a precisely calculated radiation dose to the tumor. The total dose is usually fractionated so that tumor cells can be oxygenated as surrounding cells die; this increases the sensitivity of the cells to radiation.
Body tissues and other substances are classified according to the degree to which they allow the passage of x-rays (their radiolucency) or absorb x-rays (their radiopacity). Gases are very radiolucent; fatty tissue is moderately radiolucent. Compounds containing high-atomic-weight elements, such as barium and iodine, are very radiopaque; bone and deposits of calcium salts are moderately radiopaque. Water; muscle, skin, blood, and cartilage and other connective tissue; and cholesterol and uric acid stones have intermediate density.X-ray Contrast Media. A medium" >contrast medium is a substance introduced into a structure in order to increase the radiographic contrast with surrounding tissues. The radiopaque contrast media include a variety of organic iodine compounds and the insoluble salt barium sulfate. Radiolucent contrast media are gases such as air, oxygen, or carbon dioxide.

Barium is used for gastrointestinal studies. Water-soluble, iodinated contrast media excreted by the kidneys are used for many procedures, including all types of angiography and for intravenous and retrograde urography; the most commonly used are diatrizoate and iothalamate. Those excreted by the liver are used for oral or intravenous cholangiography or cholecystography. Oily iodinated media are used for lymphangiography, bronchography, and myelography.
All iodinated contrast media can cause reactions, which may range from the common reactions of mild flushing and a feeling of warmth and nausea and vomiting to rare life-threatening reactions requiring immediate aggressive therapy. The cause of these reactions may be allergy; however, this is disputed.
A double contrast study uses both a radiopaque and a radiolucent contrast medium; for example, the walls of the stomach or intestine are coated with barium and the lumen is filled with air. The resulting radiographs clearly show the pattern of mucosal ridges.

Standard stationary anode x-ray tube; diagram in longitudinal section. From Dorland's, 2000.

Simple radiograph. A, X-ray machine; B, patient; and C, x-ray film. From Malarkey and McMorrow, 1996.

单词	x-rays
释义	x-rays x-ray or X-ray (ĕks′rā′)n. or x ray or X ray1. a. A photon of electromagnetic radiation of very short wavelength, ranging from about 10 down to 0.01 nanometers, and very high energy, ranging from about 100 up to 100,000 electron volts.b. often x-rays or X-rays A narrow beam of such photons. X-rays are used for their penetrating power in radiography, radiology, radiotherapy, and scientific research. Also called roentgen ray.2. a. A photograph taken with x-rays.b. The act or process of taking such a photograph: Did the patient move during the x-ray?tr.v. x-rayed, x-ray·ing, x-rays or X-rayed or X-ray·ing or X-rays 1. To irradiate with x-rays.2. To photograph with x-rays. [From translation of obsolete German X-Strahlen, x-rays (coined by their discoverer Wilhelm Conrad Roentgen ) : x, x, unknown factor (since x-rays were a previously unknown form of radiation) + Strahlen, pl. of Strahle, ray.] X-rays 1. Electromagnetic radiation with a wavelength between those of ultraviolet light and gamma rays.2. Short-wavelength streams of photons used to penetrate a patients’s body tissues for diagnostic purposes, such as to produce an X-ray image of the inside of the body, or as a form of therapy, such as to destroy diseased tissue. Translations X-rays (eksˈreiz) noun plural rays which can pass through many substances impossible for light to pass through, and which produce a picture of the object through which they have passed. X射線 x 射线 ˌX-ˈray noun (the process of taking) a photograph using X-rays. I'm going to hospital for an X-ray; We'll take an X-ray of your chest; (also adjective) an X-ray photograph. X光照片 x 光照片 verb to take a photograph of using X-rays. They X-rayed my arm to see if it was broken. 進行 X光攝影檢查用 x 光检查 X-rays X-rays X-rays, or roentgen rays, are electromagnetic waves in which periodically variable electric and magnetic fields are perpendicular to each other and to the direction of propagation. Thus they are identical in nature with visible light and all the other types of radiation that constitute the electromagnetic spectrum. In general, x-rays are generated as the result of energy transitions of atomic electrons caused by the bombardment of a material of high atomic weight by high-energy electrons. See Electromagnetic radiation Following W. R. Röntgen's discovery of “a new kind of ray” in 1895, other scientists found the essential experimental conditions to prove that x-rays can be polarized, diffracted by crystals, refracted in prisms and in crystals, reflected by mirrors, and diffracted by ruled gratings. See X-ray optics The range of x-rays in the electromagnetic spectrum, as excited in x-ray tubes by the bombardment of anode targets by cathode electrons under a high accelerating potential, overlaps the ultraviolet range on the order of 100 nanometers on the long-wavelength side, and the shortest-wavelength limit moves downward as voltages increase. An accelerating potential of 10⁹ volts, now readily generated, produces a wavelength of 10^-15 m (10^-6 nm). An average wavelength used in research is 0.1 nm, or about 1/6000 the wavelength of yellow light. See X-ray tube In diffraction, refraction, polarization, and interference phenomena, x-rays, together with all other related radiations, appear to act as waves. In other phenomena—such as the appearance of sharp spectral lines, a definite short-wavelength limit of the continuous “white” spectrum, the shift in wavelength of x-rays scattered by electrons in atoms (Compton effect), and the photoelectric effect—the energy seems to be propagated and transferred in quanta, called photons. See Compton effect, Electron diffraction, Neutron diffraction, Photoemission, Quantum mechanics Important uses have been found for x-rays in many fields of scientific endeavor, for example, roentgen spectrometry and roentgen diffractometry. Extensive tables of the wavelengths of x-ray emission lines in series (K, L, M, and so on) and so-called absorption edges, characteristic of the chemical elements, afford the necessary information for chemical analyses, exactly as in the case of optical emission spectra and for derivation of theories of atomic structure to account for the origin of spectra. See X-ray crystallography, X-ray diffraction, X-ray powder methods X-rays High-energy electromagnetic radiation lying between gamma rays and ultraviolet radiation in the electromagnetic spectrum. The XUV region bridges the gap between the X-ray and ultraviolet bands. X-rays, unlike light and radio waves, are usually considered in terms of photon energy, h ν, where ν is the frequency of the radiation and h is the Planck constant. X-ray energies range from about 100 electronvolts (eV) up to about 100 000 eV, corresponding to a wavelength range of about 12 nanometers (nm) to about 0.012 nm. Low-energy X-rays are sometimes called soft X-rays to distinguish them from high-energy or hard X-rays. In astronomy, thermal X-rays are produced from very high temperature gas (˜10⁶–10⁸ K), with nonthermal X-rays arising from the interaction of high-energy electrons with a magnetic field (synchrotron emission) or with low-energy photons (inverse Compton emission – see Compton scattering). See also nonthermal emission; thermal emission. x-rays [′eks ‚rāz] (physics) A penetrating electromagnetic radiation, usually generated by accelerating electrons to high velocity and suddenly stopping them by collision with a solid body, or by inner-shell transitions of atoms with atomic number greater than 10; their wavelengths range from about 10^-5 angstrom to 10³ angstroms, the average wavelength used in research being about 1 angstrom. Also known as roentgen rays; x-radiation. x-rays x-rays [eks´rāz] high-energy radiation" >electromagnetic radiation produced by the collision of a beam of electrons with a metal target in an tube" >x-ray tube; the penetrability and hardness of the x-rays increase with the voltage applied to the tube, which controls the speed with which the electrons strike the target. Called also roentgen rays. For diagnostic radiography, tube voltages in the range 80 to 120 kilovolts peak (kVp) are normally used. For radiation therapy, voltages in the 1 to 2 megavolt range are used for most treatment. Accelerating electrons to speeds high enough to produce megavoltage x-rays requires a linear accelerator (lineac). Kilovoltage lower than 80 kVp is often used for the extremities, 25 to 30 kVp is used for mammography, and up to 150 kVp can be used for chest imaging. The x-ray exposure is proportional to the tube current (milliamperage) and also to the exposure time. In diagnostic radiography, the tube voltage and current and exposure time are selected to produce a high-quality radiograph with the correct contrast and film density. In radiation therapy, these exposure factors are selected to deliver a precisely calculated radiation dose to the tumor. The total dose is usually fractionated so that tumor cells can be oxygenated as surrounding cells die; this increases the sensitivity of the cells to radiation. Body tissues and other substances are classified according to the degree to which they allow the passage of x-rays (their radiolucency) or absorb x-rays (their radiopacity). Gases are very radiolucent; fatty tissue is moderately radiolucent. Compounds containing high-atomic-weight elements, such as barium and iodine, are very radiopaque; bone and deposits of calcium salts are moderately radiopaque. Water; muscle, skin, blood, and cartilage and other connective tissue; and cholesterol and uric acid stones have intermediate density.X-ray Contrast Media. A medium" >contrast medium is a substance introduced into a structure in order to increase the radiographic contrast with surrounding tissues. The radiopaque contrast media include a variety of organic iodine compounds and the insoluble salt barium sulfate. Radiolucent contrast media are gases such as air, oxygen, or carbon dioxide. Barium is used for gastrointestinal studies. Water-soluble, iodinated contrast media excreted by the kidneys are used for many procedures, including all types of angiography and for intravenous and retrograde urography; the most commonly used are diatrizoate and iothalamate. Those excreted by the liver are used for oral or intravenous cholangiography or cholecystography. Oily iodinated media are used for lymphangiography, bronchography, and myelography. All iodinated contrast media can cause reactions, which may range from the common reactions of mild flushing and a feeling of warmth and nausea and vomiting to rare life-threatening reactions requiring immediate aggressive therapy. The cause of these reactions may be allergy; however, this is disputed. A double contrast study uses both a radiopaque and a radiolucent contrast medium; for example, the walls of the stomach or intestine are coated with barium and the lumen is filled with air. The resulting radiographs clearly show the pattern of mucosal ridges.Standard stationary anode x-ray tube; diagram in longitudinal section. From Dorland's, 2000.Simple radiograph. A, X-ray machine; B, patient; and C, x-ray film. From Malarkey and McMorrow, 1996. ThesaurusSeeX-ray
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