# Absorption cross section

﻿
Absorption cross section

Absorption cross section is a measure for the probability of an absorption process. More generally, the term cross section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering, photoabsorption, etc. (Note that light in this context is described as consisting of quasi-particles, i.e., photons.)

In the context of ozone shielding of ultraviolet light, absorption cross section is the ability of a molecule to absorb a photon of a particular wavelength and polarization.Analogously, in the context of nuclear engineering it refers to the probability of a particle (usually a neutron) being absorbed by a nucleus. Although the units are given as an area, it does not refer to an actual size area, at least partially because the density or state of the target molecule will affect the probability of absorption. Quantitatively, the number dN of photons absorbed, between the points x and x + dx along the path of a beam is the product of the number N of photons penetrating to depth x times the number n of absorbing molecules per unit volume times the absorption cross section σ:

:$frac\left\{dN\right\}\left\{dx\right\}= -N n sigma$.

Concept of cross-section is closely related to mass attenuation coefficient and for a given particle and its energy cross-sections of the target material can be calculated from mass absorption coefficient using:

:$frac\left\{dN\right\}\left\{dx\right\}= \left(mu/ ho\right) * u m_a$

where:
* μ/ρ is mass attenuation coefficient
* ma is atomic molar mass in g/mol
* u is atomic mass unit (1/12 of the mass of Carbon-12) equal to 1.6605402E-24g

ee also

*Cross section (physics)
*Photoemission cross section
*Nuclear cross section
*Scattering cross-section
*Cross Section
*Mean Free Path
*Compton edge
*Compton scattering
*Transmittance
*Attenuation
*High energy X-rays
*Attenuation coefficient

References

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• absorption cross-section — sugerties skerspjūvis statusas T sritis fizika atitikmenys: angl. absorption cross section; cross section for absorption vok. Absorptionsquerschnitt, m; Absorptionswirkungsquerschnitt, m; Wirkungsquerschnitt für Absorption, m rus. сечение… …   Fizikos terminų žodynas

• two-photon absorption cross-section — dvifotonės sugerties skerspjūvis statusas T sritis radioelektronika atitikmenys: angl. two photon absorption cross section vok. Zweiphotonenabsorptionsquerschnitt, m rus. сечение двухфотонного поглощения, n pranc. section d absorption à deux… …   Radioelektronikos terminų žodynas

• Cross section — may refer to: Cross section (geometry), the intersection of a 3 dimensional body with a plane Cross sectional views in architecture engineering Radar cross section, the unit of measure of how detectable an object is with a radar Cross section… …   Wikipedia

• cross-section for absorption — sugerties skerspjūvis statusas T sritis fizika atitikmenys: angl. absorption cross section; cross section for absorption vok. Absorptionsquerschnitt, m; Absorptionswirkungsquerschnitt, m; Wirkungsquerschnitt für Absorption, m rus. сечение… …   Fizikos terminų žodynas

• Cross section (physics) — A cross section is the effective area which governs the probability of some scattering or absorption event. Together with particle density and path length, it can be used to predict the total scattering probability via the Beer Lambert law. In… …   Wikipedia

• cross section — 1. a section made by a plane cutting anything transversely, esp. at right angles to the longest axis. 2. a piece so cut off. 3. a photograph, diagram, or other pictorial representation of such a section. 4. the act of cutting anything across. 5.… …   Universalium

• Neutron cross section — Science with Neutrons Foundations Neutron temperature Flux · Radiation  …   Wikipedia

• Photoionisation cross section — in the context of condensed matter physics refers to the probability of a particle (usually an electron) being emitted from its electronic state. Cross section in photoemission The photoemission is a useful experimental method for the… …   Wikipedia

• 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… …   Wikipedia

• Neutron cross-section — The total neutron cross section of an isotope of a chemical element is the effective cross sectional area that an atom of that isotope presents to neutron scattering and absorption. cattering versus absorptionWhen a neutron approaches an atomic… …   Wikipedia