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X-ray Detectors
X-ray detectors are devices used to measure the flux, spatial distribution, spectrum, and/or other properties of X-rays. Detectors can be divided into two major categories: imaging detectors (such as photographic plates and X-ray film (photographic film), now mostly replaced by various digitizing devices like image plates or flat panel detectors) and dose measurement devices (such as ionization chambers, Geiger counters, and dosimeters used to measure the local radiation exposure, dose, and/or dose rate, for example, for verifying that radiation protection equipment and procedures are effective on an ongoing basis). X-ray imaging To obtain an image with any type of image detector the part of the patient to be X-rayed is placed between the X-ray source and the image receptor to produce a shadow of the internal structure of that particular part of the body. X-rays are partially blocked ("attenuated") by dense tissues such as bone, and pass more easily through soft tissues. Areas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. The most common minerals of barium are baryte ( barium sulfate, BaSO4) and witherite (barium carbonate, BaCO3). The name ''barium'' originates from the alchemical derivative "baryta", from Greek (), meaning 'heavy'. ''Baric'' is the adjectival form of barium. Barium was identified as a new element in 1774, but not reduced to a metal until 1808 with the advent of electrolysis. Barium has few industrial applications. Historically, it was used as a getter for vacuum tubes and in oxide form as the emissive coating on indirectly heated cathodes. It is a component of YBCO (high-temperature superconductors) and electroceramics, and is added to steel and cast iron to reduce the size of carbon grains within the microstructure. Barium compounds ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transparency And Translucency
In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions are much larger than the wavelengths of the photons in question), the photons can be said to follow Snell's law. Translucency (also called translucence or translucidity) allows light to pass through, but does not necessarily (again, on the macroscopic scale) follow Snell's law; the photons can be scattered at either of the two interfaces, or internally, where there is a change in index of refraction. In other words, a translucent material is made up of components with different indices of refraction. A transparent material is made up of components with a uniform index of refraction. Transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. The opposit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redox
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. There are two classes of redox reactions: * ''Electron-transfer'' – Only one (usually) electron flows from the reducing agent to the oxidant. This type of redox reaction is often discussed in terms of redox couples and electrode potentials. * ''Atom transfer'' – An atom transfers from one substrate to another. For example, in the rusting of iron, the oxidation state of iron atoms increases as the iron converts to an oxide, and simultaneously the oxidation state of oxygen decreases as it accepts electrons released by the iron. Although oxidation reactions are commonly associated with the formation of oxides, other chemical species can serve the same function. In hydrogen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Latent Image
{{citations needed, date=November 2015 A latent image is an invisible image produced by the exposure to light of a photosensitive material such as photographic film. When photographic film is developed, the area that was exposed darkens and forms a visible image. In the early days of photography, the nature of the invisible change in the silver halide crystals of the film's emulsion coating was unknown, so the image was said to be "latent" until the film was treated with photographic developer. In more physical terms, a latent image is a small cluster of metallic silver atoms formed in or on a silver halide crystal due to reduction of interstitial silver ions by photoelectrons (a photolytic silver cluster). If intense exposure continues, such photolytic silver clusters grow to visible sizes. This is called ''printing out'' the image. On the other hand, the formation of a visible image by the action of photographic developer is called ''developing out'' the image. The size of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystal Defect
A crystallographic defect is an interruption of the regular patterns of arrangement of atoms or molecules in crystalline solids. The positions and orientations of particles, which are repeating at fixed distances determined by the unit cell parameters in crystals, exhibit a periodic crystal structure, but this is usually imperfect.Ehrhart, P. (1991Properties and interactions of atomic defects in metals and alloys, volume 25 of Landolt-Börnstein, New Series III, chapter 2, p. 88, Springer, Berlin Several types of defects are often characterized: point defects, line defects, planar defects, bulk defects. Topological homotopy establishes a mathematical method of characterization. Point defects Point defects are defects that occur only at or around a single lattice point. They are not extended in space in any dimension. Strict limits for how small a point defect is are generally not defined explicitly. However, these defects typically involve at most a few extra or missing atoms. Lar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrons
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron's mass is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum ( spin) of a half-integer value, expressed in units of the reduced Planck constant, . Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ionised
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected. Uses Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps. It is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber. The io ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Image Resolution
Image resolution is the detail an image holds. The term applies to digital images, film images, and other types of images. "Higher resolution" means more image detail. Image resolution can be measured in various ways. Resolution quantifies how close lines can be to each other and still be visibly ''resolved''. Resolution units can be tied to physical sizes (e.g. lines per mm, lines per inch), to the overall size of a picture (lines per picture height, also known simply as lines, TV lines, or TVL), or to angular subtense. Instead of single lines, line pairs are often used, composed of a dark line and an adjacent light line; for example, a resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm). Photographic lens and film resolution are most often quoted in line pairs per millimeter. Types The resolution of digital cameras can be described in many different ways. Pixel count The term ''resolution'' is o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silver Bromide
Silver bromide (AgBr) is a soft, pale-yellow, water-insoluble salt well known (along with other silver halides) for its unusual sensitivity to light. This property has allowed silver halides to become the basis of modern photographic materials. AgBr is widely used in photographic films and is believed by some to have been used for making the Shroud of Turin. The salt can be found naturally as the mineral bromargyrite. Preparation Although the compound can be found in mineral form, AgBr is typically prepared by the reaction of silver nitrate with an alkali bromide, typically potassium bromide: :AgNO3(aq) + KBr(aq) → AgBr(s)+ KNO3(aq) Although less convenient, the compound can also be prepared directly from its elements. Modern preparation of a simple, light-sensitive surface involves forming an emulsion of silver halide crystals in a gelatine, which is then coated onto a film or other support. The crystals are formed by precipitation in a controlled environment to produce smal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silver Halide
A silver halide (or silver salt) is one of the chemical compounds that can form between the element silver (Ag) and one of the halogens. In particular, bromine (Br), chlorine (Cl), iodine (I) and fluorine (F) may each combine with silver to produce silver bromide (AgBr), silver chloride (AgCl), silver iodide (AgI), and three forms of silver fluoride, respectively. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX. Although most silver halides involve silver atoms with oxidation states of +1 (Ag+), silver halides in which the silver atoms have oxidation states of +2 (Ag2+) are known, of which silver(II) fluoride is the only known stable one. Silver halides are light-sensitive chemicals, and are commonly used in photographic film and paper. Applications Light sensitivity Silver halides are used in photographic film and photographic paper, including graphic art film and paper, where silver halide crystals in g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thorotrast
Thorotrast is a suspension containing particles of the radioactive compound thorium dioxide, ThO2; it was used as a radiocontrast agent in clinical radiography in the 1930s to 1950s. It is no longer used clinically. Thorium compounds produce excellent images because of thorium's high opacity to X-rays (it has a high cross section for absorption). However, thorium is retained in the body, and it is radioactive, emitting harmful alpha radiation as it decays. Because the suspension offered high image quality and had virtually no immediate side-effects compared to the alternatives available at the time, Thorotrast became widely used after its introduction in 1931. António Egas Moniz contributed to its development. About 2 to 10 million patients worldwide have been treated with Thorotrast. However, today it has shown an increase risk in certain cancers such as cholangiocarcinomas, angiosarcomas, hepatocellular carcinoma and hepatic fibrosis of the liver. Safety Even at the time o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
