翻訳と辞書 Words near each other ・ Nuclear bunker buster ・ Nuclear C*-algebra ・ Nuclear cap-binding protein complex ・ Nuclear chain cell ・ Nuclear chain fiber ・ Nuclear chain reaction ・ Nuclear chemistry ・ Nuclear Cities Initiative ・ Nuclear collision length ・ Nuclear Command Authority ・ Nuclear Command Authority (India) ・ Nuclear Compton Telescope ・ Nuclear Control Institute ・ Nuclear Cowboy ・ Nuclear criticality safety ・ Nuclear cross section ・ Nuclear damper ・ Nuclear data ・ Nuclear Dawn ・ Nuclear Daydream ・ Nuclear Death ・ Nuclear Death discography ・ Nuclear Debate ・ Nuclear debate ・ Nuclear decommissioning ・ Nuclear Decommissioning Authority ・ Nuclear density ・ Nuclear density gauge ・ Nuclear densometer ・ Nuclear depth bomb Dictionary Lists mini英和辞書 mini和英辞書 Webster 1913 Latin-English FOLDOC Wikipedia English ウィキペディア

翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Nuclear cross section ： ウィキペディア英語版 Nuclear cross section The nuclear cross section of a nucleus is used to characterize the probability that a nuclear reaction will occur. The concept of a nuclear cross section can be quantified physically in terms of "characteristic area" where a larger area means a larger probability of interaction. The standard unit for measuring a nuclear cross section (denoted as σ) is the barn, which is equal to 10−28 m² or 10−24 cm². Cross sections can be measured for all possible interaction processes together, in which case they are called total cross sections, or for specific processes, distinguishing elastic scattering and inelastic scattering; of the latter, amongst neutron cross sections the absorption cross sections are of particular interest. In nuclear physics it is conventional to consider the impinging particles as point particles having negligible diameter. Cross sections can be computed for any sort of process, such as capture scattering, production of neutrons, etc. In many cases, the number of particles emitted or scattered in nuclear processes is not measured directly; one merely measures the attenuation produced in a parallel beam of incident particles by the interposition of a known thickness of a particular material. The cross section obtained in this way is called the total cross section and is usually denoted by a σ or σT. Typical nuclear radii are of the order 10−14 m. Assuming spherical shape, we therefore expect the cross sections for nuclear reactions to be of the order of π''r'' ² or 10−28 m². This quantity is named the barn, and is the unit in which nuclear cross sections are usually expressed. Observed cross sections vary enormously - for example, slow neutrons absorbed by the (n, $\backslash gamma$) reaction show a cross section much higher than 1,000 barns in some cases (boron-10, cadmium-113, and xenon-135), while the cross sections for transmutations by gamma-ray absorption are in the region of 0.001 barn. ==Macroscopic cross section== Nuclear cross sections are used in determining the nuclear reaction rate, and are governed by the reaction rate equation for a particular set of particles (usually viewed as a "beam and target" thought experiment where one particle or nucleus is the "target" (at rest ) and the other is treated as a "beam" (with a given energy )). For neutron interactions incident upon a thin sheet of material (ideally made of a single type of isotope), the nuclear reaction rate equation is written as: :$r\_x\; =\; \backslash Phi\; \backslash \; \backslash sigma\_x\; \backslash \; \backslash rho\_A\; =\; \backslash Phi\; \backslash Sigma\_x$ where: * $r\_x$ : number of reactions of type x, units: () * $\backslash Phi$ : neutron beam flux, units: () * $\backslash sigma\_x$ : microscopic cross section for reaction $x$, units: () (usually barns or cm2). * $\backslash rho\_A$ : density of atoms in the target in units of () * $\backslash Sigma\_x\; \backslash equiv\; \backslash sigma\_x\; \backslash \; \backslash rho\_A$: macroscopic cross-section () Types of reactions frequently encountered are ''s'': scattering, $\backslash gamma$: radiative capture, ''a'': absorption (radiative capture belongs to this type), ''f'': fission, the corresponding notation for cross-sections being: $\backslash sigma\_s$, $\backslash sigma\_\backslash gamma$, $\backslash sigma\_a$, etc. A special case is the total cross-section $\backslash sigma\_t$, which gives the probability of a neutron to undergo any sort of reaction ($\backslash sigma\_t\; =\; \backslash sigma\_s\; +\; \backslash sigma\_\backslash gamma\; +\; \backslash sigma\_f\; +\; ...$). Formally, the equation above ''defines'' the macroscopic neutron cross-section (for reaction x) as the proportionality constant between a neutron flux incident on a (thin) piece of material and the number of reactions that occur (per unit volume) in that material. The distinction between macroscopic and microscopic cross-section is that the former is a property of a specific lump of material (with its density), while the latter is an intrinsic property of a type of nuclei. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nuclear cross section」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.