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Gamma-Ray Imaging Spectrometer
The Gamma-Ray Imaging Spectrometer (GRIS) was a gamma-ray spectrometer instrument on a weather balloon, balloon-borne airborne observatory. It used germanium detectors to achieve high resolution spectroscopy. GRIS was operated from 1988 to 1995 by NASA's Goddard Space Flight Center, which called it "arguably one of the most successful gamma-ray balloon programs in history". History GRIS followed earlier gamma ray spectroscopy work by Bell Labs/Sandia National Laboratories and co-investigators Marvin Leventhal and Bonnard Teegarden, including the LEGS spectrometer. GRIS was selected for a balloon program after the removal of a high-resolution gamma-ray spectrometer from the payload of what would become the Compton Gamma Ray Observatory. GRIS first flew in May 1988 from Alice Springs, Australia. During its first several flights, the instrument definitively measured the gamma ray spectral line, lines from Supernova 1987A, including that of Isotopes of cobalt, 56Co, and the positron ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gamma-ray Spectrometer
A gamma-ray spectrometer (GRS) is an instrument for measuring the distribution (or spectrum—see figure) of the intensity of gamma radiation versus the energy of each photon. The study and analysis of gamma-ray spectra for scientific and technical use is called gamma spectroscopy, and gamma-ray spectrometers are the instruments which observe and collect such data. Because the energy of each photon of EM radiation is proportional to its frequency, gamma rays have sufficient energy that they are typically observed by counting individual photons. Gamma-ray spectroscopy Atomic nuclei have an energy-level structure somewhat analogous to the energy levels of atoms, so that they may emit (or absorb) photons of particular energies, much as atoms do, but at energies that are thousands to millions of times higher than those typically studied in optical spectroscopy. (Note that the short-wavelength high-energy end, of the atomic spectroscopy energy range (few eV to few hundred keV), g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Astrophysical Journal
''The Astrophysical Journal'', often abbreviated ''ApJ'' (pronounced "ap jay") in references and speech, is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler. The journal discontinued its print edition and became an electronic-only journal in 2015. Since 1953 ''The Astrophysical Journal Supplement Series'' (''ApJS'') has been published in conjunction with ''The Astrophysical Journal'', with generally longer articles to supplement the material in the journal. It publishes six volumes per year, with two 280-page issues per volume. ''The Astrophysical Journal Letters'' (''ApJL''), established in 1967 by Subrahmanyan Chandrasekhar as Part 2 of ''The Astrophysical Journal'', is now a separate journal focusing on the rapid publication of high-impact astronomical research. The three journals were published by the University of Chicago Press for the American Astronomical Society u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Field Of View
The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans and animals In the context of human and primate vision, the term "field of view" is typically only used in the sense of a restriction to what is visible by external apparatus, like when wearing spectacles or virtual reality goggles. Note that eye movements are allowed in the definition but do not change the field of view when understood this way. If the analogy of the eye's retina working as a sensor is drawn upon, the corresponding concept in human (and much of animal vision) is the visual field. It is defined as "the number of degrees of visual angle during stable fixation of the eyes".Strasburger, Hans; Pöppel, Ernst (2002). Visual Field. In G. Adelman & B.H. Smith (Eds): ''Encyclopedia of Neuroscience''; 3rd edition, on CD-ROM. El ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Henry (unit)
The henry (symbol: H) is the unit of electrical inductance in the International System of Units (SI). If a current of 1 ampere flowing through a coil produces flux linkage of 1 weber turn, that coil has a self inductance of 1 henry. The unit is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791–1867) in England. Definition The inductance of an electric circuit is one henry when an electric current that is changing at one ampere per second results in an electromotive force of one volt across the inductor: :\displaystyle V(t)= L \frac, where ''V''(''t'') denotes the resulting voltage across the circuit, ''I''(''t'') is the current through the circuit, and ''L'' is the inductance of the circuit. The henry is a derived unit based on four of the seven base units of the International System of Units: kilogram (kg), metre (m), second (s), and ampere (A). E ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standard Deviation
In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while a high standard deviation indicates that the values are spread out over a wider range. Standard deviation may be abbreviated SD, and is most commonly represented in mathematical texts and equations by the lower case Greek letter σ (sigma), for the population standard deviation, or the Latin letter '' s'', for the sample standard deviation. The standard deviation of a random variable, sample, statistical population, data set, or probability distribution is the square root of its variance. It is algebraically simpler, though in practice less robust, than the average absolute deviation. A useful property of the standard deviation is that, unlike the variance, it is expressed in the same unit as the data. The standard deviation o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronic Anticoincidence
Electronic anticoincidence is a method (and its associated hardware) widely used to suppress unwanted, "background" events in high energy physics, experimental particle physics, gamma-ray spectroscopy, gamma-ray astronomy, experimental nuclear physics, and related fields. In the typical case, a high-energy interaction, or event, that it is desired to study occurs and is detected by some kind of electronic detector, creating a fast electronic pulse in the associated nuclear electronics. But the desired events are mixed up with a significant number of other events, produced by other particles or other processes, which create indistinguishable events in the detector. Very often it is possible to arrange other physical photon or particle detectors to intercept the unwanted background events, producing essentially simultaneous pulses that can be used with fast electronics to reject, or veto, the unwanted background. Gamma-ray astronomy Early experimenters in X-ray and gamma-ray astron ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sodium Iodide
Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions (I−) in a crystal lattice. It is used mainly as a nutritional supplement and in organic chemistry. It is produced industrially as the salt formed when acidic iodides react with sodium hydroxide. It is a chaotropic salt. Uses Food supplement Sodium iodide, as well as potassium iodide, is commonly used to treat and prevent iodine deficiency. Iodized table salt contains 10 ppm iodide. Organic synthesis Sodium iodide is used for conversion of alkyl chlorides into alkyl iodides. This method, the Finkelstein reaction, relies on the insolubility of sodium chloride in acetone to drive the reaction: ::R–Cl + NaI → R–I + NaCl Nuclear medicine Some radioactive iodide salts of sodium, including Na 125I and Na 131I, have radio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Liquid Nitrogen
Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is widely used as a coolant. Physical properties The diatomic character of the N2 molecule is retained after liquefaction. The weak van der Waals interaction between the N2 molecules results in little interatomic interaction, manifested in its very low boiling point. The temperature of liquid nitrogen can readily be reduced to its freezing point by placing it in a vacuum chamber pumped by a vacuum pump. Liquid nitrogen's efficiency as a coolant is limited by the fact that it boils immediately on contact with a warmer object, enveloping the object in an insulating layer of nitrogen gas bubbles. This effect, known as the Leidenfrost effect, occurs when any liquid comes in contact with a surface which is significantly hotter than its b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronvolt
In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. When used as a unit of energy, the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C). Under the 2019 redefinition of the SI base units, this sets 1 eV equal to the exact value Historically, the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences, because a particle with electric charge ''q'' gains an energy after passing through a voltage of ''V.'' Since ''q'' must be an integer multiple of the elementary charge ''e'' for any isolated particle, the gained energy in units of electronvolts conveniently equals that integer times the voltage. It is a common unit of ene ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extrinsic Semiconductor
An extrinsic semiconductor is one that has been '' doped''; during manufacture of the semiconductor crystal a trace element or chemical called a doping agent has been incorporated chemically into the crystal, for the purpose of giving it different electrical properties than the pure semiconductor crystal, which is called an ''intrinsic semiconductor''. In an extrinsic semiconductor it is these foreign dopant atoms in the crystal lattice that mainly provide the charge carriers which carry electric current through the crystal. The doping agents used are of two types, resulting in two types of extrinsic semiconductor. An '' electron donor'' dopant is an atom which, when incorporated in the crystal, releases a mobile conduction electron into the crystal lattice. An extrinsic semiconductor which has been doped with electron donor atoms is called an n-type semiconductor, because the majority of charge carriers in the crystal are negative electrons. An ''electron acceptor'' dopant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
INTEGRAL
In mathematics, an integral assigns numbers to functions in a way that describes displacement, area, volume, and other concepts that arise by combining infinitesimal data. The process of finding integrals is called integration. Along with differentiation, integration is a fundamental, essential operation of calculus,Integral calculus is a very well established mathematical discipline for which there are many sources. See and , for example. and serves as a tool to solve problems in mathematics and physics involving the area of an arbitrary shape, the length of a curve, and the volume of a solid, among others. The integrals enumerated here are those termed definite integrals, which can be interpreted as the signed area of the region in the plane that is bounded by the graph of a given function between two points in the real line. Conventionally, areas above the horizontal axis of the plane are positive while areas below are negative. Integrals also refer to the concept of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University Of Maryland, College Park
The University of Maryland, College Park (University of Maryland, UMD, or simply Maryland) is a public land-grant research university in College Park, Maryland. Founded in 1856, UMD is the flagship institution of the University System of Maryland. It is also the largest university in both the state and the Washington metropolitan area, with more than 41,000 students representing all fifty states and 123 countries, and a global alumni network of over 388,000. Together, its 12 schools and colleges offer over 200 degree-granting programs, including 92 undergraduate majors, 107 master's programs, and 83 doctoral programs. UMD is a member of the Association of American Universities and competes in intercollegiate athletics as a member of the Big Ten Conference. The University of Maryland's proximity to the nation's capital has resulted in many research partnerships with the federal government; faculty receive research funding and institutional support from many agencies, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
