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The attenuation coefficient of a volume, denoted μ, is defined as [6] =, where Φ e is the radiant flux;; z is the path length of the beam.; Note that for an attenuation coefficient which does not vary with z, this equation is solved along a line from =0 to as:
In nuclear physics, the concept of a neutron cross section is used to express the likelihood of interaction between an incident neutron and a target nucleus. The neutron cross section σ can be defined as the area in cm 2 for which the number of neutron-nuclei reactions taking place is equal to the product of the number of incident neutrons that would pass through the area and the number of ...
It characterizes the absorption of neutrons by a single nucleus in the resonance region and is measured in barnes. The use of the effective resonance integral simplifies quantitative calculations of resonance absorption without detailed consideration of neutron interaction at deceleration.
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", which is typically at rest, and the other is treated as a "beam", which is a projectile with a given energy).
The absorption neutron cross section of an isotope of a chemical element is the effective cross-sectional area that an atom of that isotope presents to absorption and is a measure of the probability of neutron capture. It is usually measured in barns. Absorption cross section is often highly dependent on neutron energy. In general, the ...
The mass attenuation coefficient can be looked up or calculated for any material and energy combination using the National Institute of Standards and Technology (NIST) databases. [ 7 ] [ 8 ] In X-ray radiography the calculation of the mean free path is more complicated, because photons are not mono-energetic, but have some distribution of ...
a a = symmetry/asymmetry extent coefficient for the numbers of neutrons/protons, ... μ = Linear absorption coefficient; x = Thickness of substance
In addition, by measuring the ratios of neutron attenuation to gamma-ray attenuation, it is possible to analyse the elemental composition of scanned substances. [ 9 ] An upgraded version of the scanner, named the AC6015XN Air Cargo Scanner and co-developed by Nuctech and CSIRO, was developed and trialled in Beijing in 2009.
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