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The '''nuclear [[cross section (physics)|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 (unit)|barn]], which is equal to 10<sup>−28</sup> m² or 10<sup>−24</sup> cm². Cross sections can be measured for all possible interaction processes together, in which case they are called  [[total cross section]]s, or for specific processes, distinguishing [[elastic scattering]] and [[inelastic scattering]]; of the latter, amongst [[neutron cross section]]s the  [[absorption cross section]]s are of particular interest.
== just two back ==


In nuclear physics it is conventional to consider the impinging particles as [[point particle]]s 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 σ<sub>T</sub>.  
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The typical nuclear radius is of the order of 10<sup>−12</sup> cm. We might therefore expect the cross sections for nuclear reactions to be of the order of π''r''&thinsp;² or roughly 10<sup>−24</sup> cm² and this unit is given its own name, the [[barn (unit)|barn]], and is the unit in which cross sections are usually expressed. Actually the observed cross sections vary enormously. Thus for [[thermal neutron|slow neutron]]s absorbed by the (n, <math>\gamma</math>) reaction, the cross section is much higher than 1,000 barns in some cases (boron-10, cadmium-113, and xenon-135), while the cross sections for [[Nuclear transmutation|transmutation]]s by [[gamma ray|gamma-ray]] absorption are in the region of 0.001 barn.
== naturally do not want this big cake falls Xiao Yan hands. ==


==Macroscopic cross section==
That we today would easily give Han Feng Hao settled hatred, lest he die not peace. '<br><br>voice down, two forceful momentum of the body is the storm surge from the gold and silver out of the old couple finally come together, enveloped the [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-8.html casio 腕時計 スタンダード] entire auction!<br><br>'good, old silver and old gold, killed this kid, and then together we will' Xiao door 'completely cleaned up! maple city can not afford to fall in the hands of these guys!' in gold and silver [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-2.html 腕時計 casio] behind the old couple, who used to belong to members of the Black Union Some guys, to see the former's move, Lima face 'color' [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-1.html カシオ スタンダード 腕時計] excited loud drink up, for Maple City, they are also extremely coveted, naturally do not want this big cake [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-3.html カシオ 腕時計 電波 ソーラー] falls Xiao Yan hands.<br><br>hear the support of all, gold and silver are also two old gloomy [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-3.html カシオ 電波時計 腕時計] smile, that gushed from the body's momentum, but also gradually become strong<br><br>under two old gold and silver so powerful momentum oppression, auction among most people face, 'color' reddened
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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" [typically at rest] and the other is treated as a "beam" [projectile with a given energy]).
== this inner courtyard ==


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:
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:<math>r_x = \Phi  \  \sigma_x \ \rho_A = \Phi \Sigma_x </math>
== the most dangerous one ==


where:
Wow, some can not avoid, then is the fastest means never before issuing its roar, will the killing, so the shuttle for a moment in the forest, a mountain just before it appears.<br><br>supple leapt peaks, Xiao Yan in the hillside to find a safe place that, like a sigh of relief this relief, like collapse like an ass and sat down, kill today this can really make too His spirit completely tense up.<br><br>today [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-12.html カシオ 時計 電波] might also be counted XiaoYan since entering the Plains, the most dangerous [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-14.html カシオ 腕時計 ソーラー 電波] one, if not he will act decisively reel [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-0.html カシオ 時計 価格] abandoned, probably still difficult to escape charges of days to kill, stars were, if not he cast lotus fire destroyed it, I am afraid of really difficult to defeat, but the fire destroyed the lotus is a big kill, consumption is extremely horrible, once cast, Xiao Yan [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-15.html カシオ gps 時計] inevitably will [http://www.ispsc.edu.ph/nav/japandi/casio-rakuten-9.html カシオ 掛け時計] enter the weakest state, therefore, if not a last resort urgent moment, Xiao Yan does not easily be the
* <math>r_x</math> : number of reactions of type x, units: [1/time/volume]
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* <math>\Phi</math> : neutron beam flux, units: [1/area/time]
<ul>
* <math>\sigma_x</math> : microscopic cross section for reaction <math>x</math>, units: [area] (usually [[barn (unit)|barns]] or cm<sup>2</sup>).
 
* <math>\rho_A</math> : density of atoms in the target in units of [1/volume]
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* <math>\Sigma_x \equiv \sigma_x \ \rho_A</math>: macroscopic cross-section [1/length]
 
 
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Types of reactions frequently encountered are ''s'': scattering, <math>\gamma</math>: radiative capture, ''a'': absorption (radiative capture belongs to this type), ''f'': fission, the corresponding notation for cross-sections being: <math>\sigma_s</math>, <math>\sigma_\gamma</math>, <math>\sigma_a</math>, etc. A special case is the total cross-section <math>\sigma_t</math>, which gives the probability of a neutron to undergo any sort of reaction (<math>\sigma_t = \sigma_s + \sigma_\gamma + \sigma_f + ...</math>).
    
 
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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.
    
 
</ul>
==See also==
* [[Neutron cross-section]]
* [[Scattering cross-section]]
 
==References==
{{More footnotes|date=December 2009}}
* ''Nuclear Reactor Analysis'' by [[James J. Duderstadt]] and [[Louis J. Hamilton]] - ''Published by John Wiley & Sons, Inc.''
* {{cite book | author=Perkins, Donald H. | title=Introduction to High Energy Physics | publisher=Cambridge University Press | year=1999 | isbn=0-521-62196-8}}
*{{Cite journal
  | last =Mubarakmand
   | first =Samar
  | authorlink =Samar Mubarakmand
  | coauthors =[[Masud Ahmad]], M. Anwar, M.S. Chaudhry
  | title =Cross-section measurements with a neutron generator
  | journal =The Nucleus
  | volume =42
  | issue =1-2
   | pages =115–185
  | publisher =PINSTECH
  | location =Nilore, Islamabad
  | year =1977
  | url =
  | issn =
  | doi =
  | id =
  | accessdate =2011 }}
[[Category:Scattering]]

Latest revision as of 04:14, 3 April 2014

just two back

The sky, Xiao Yan Emperor and soul up to lofty-like body that is void marching backwards a few steps, each step down, there are a few little knowledge カシオ 掛け時計 of space burst into a dark nothingness.

However, just two back, in turn is カシオ電波ソーラー腕時計 a storm washed out, this battle is not extremely brilliant, but it is strong to extreme forces collide, no one can imagine, when the two behemoths fight with lofty metering When, that is how have the visual impact.
collision http://alleganycountyfair.org/sitemap.xml between
, FY shock, thunder flashes, as if heaven カシオ ソーラー電波腕時計 and earth, are in for this and other encounters and trembling.

two behemoths battle, for the Central Plains, this is obviously caused great damage upon the earth, constantly shaking violently, huge cracks in the abyss, almost to the Central Plains into two, all creatures, In this and so are fighting hard 時計 カシオ work, just that the aftermath of a minor, a fighting holy enough to be strong 相关的主题文章：

naturally do not want this big cake falls Xiao Yan hands.

That we today would easily give Han Feng Hao settled hatred, lest he die not peace. '

voice down, two forceful momentum of the body is the storm surge from the gold and silver out of the old couple finally come together, enveloped the casio 腕時計 スタンダード entire auction!

'good, old silver and old gold, killed this kid, and then together we will' Xiao door 'completely cleaned up! maple city can not afford to fall in the hands of these guys!' in gold and silver 腕時計 casio behind the old couple, who used to belong to members of the Black Union Some guys, to see the former's move, Lima face 'color' カシオ スタンダード 腕時計 excited loud drink up, for Maple City, they are also extremely coveted, naturally do not want this big cake カシオ 腕時計 電波 ソーラー falls Xiao Yan hands.

hear the support of all, gold and silver are also two old gloomy カシオ 電波時計 腕時計 smile, that gushed from the body's momentum, but also gradually become strong

under two old gold and silver so powerful momentum oppression, auction among most people face, 'color' reddened 相关的主题文章：

this inner courtyard

'Really is skilled are bold ah, this inner courtyard, really horrible' Xiao Yan swallowed, in the heart muttered.

'Well, bold? which I think they are burned.' 'medicine' old snorted.

'how? ah I see seems to be nothing.' Xiao Yan surprised Road.

'Hey, now they have relied on the blockade of cage space is indeed nothing, but this is only a stopgap measure, even with カシオ腕時計 メンズ that space cage, there could not have been the fall of heart inflammation blockade in the tower.'

'medicine' old hehe smiles: 'Fire can カシオ 腕時計 チタン not be blocked sparse, which fall singular heart inflammation fire between heaven and earth, but by the birth of a truly destructive force within the hospital so blocked, it is like is built on a volcano barriers in general, you have seen the カシオ 腕時計 バンド volcano can block up? Now casio 腕時計 デジタル repressed, only in the storage power, until the outbreak of this カシオ 時計 電波 ソーラー day Lianqi burning towers, the 相关的主题文章：

the most dangerous one

Wow, some can not avoid, then is the fastest means never before issuing its roar, will the killing, so the shuttle for a moment in the forest, a mountain just before it appears.

supple leapt peaks, Xiao Yan in the hillside to find a safe place that, like a sigh of relief this relief, like collapse like an ass and sat down, kill today this can really make too His spirit completely tense up.

today カシオ 時計 電波 might also be counted XiaoYan since entering the Plains, the most dangerous カシオ 腕時計 ソーラー 電波 one, if not he will act decisively reel カシオ 時計 価格 abandoned, probably still difficult to escape charges of days to kill, stars were, if not he cast lotus fire destroyed it, I am afraid of really difficult to defeat, but the fire destroyed the lotus is a big kill, consumption is extremely horrible, once cast, Xiao Yan カシオ gps 時計 inevitably will カシオ 掛け時計 enter the weakest state, therefore, if not a last resort urgent moment, Xiao Yan does not easily be the 相关的主题文章：

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