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cross sections | A Wisdom Archive on cross sections | | cross sections A selection of articles related to cross sections | |
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cross sections
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ARTICLES RELATED TO cross sections | |
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| | |  cross sections: Encyclopedia II - Feynman diagram - Motivation and historyThe problem of calculating scattering cross sections in particle physics reduces to summing over the amplitudes of all possible intermediate states (each corresponding to one term in the perturbation expansion which is known as the Dyson series). These states can be represented by Feynman diagrams, which are much easier to keep track of than frequently tortuous calculations. Feynman showed how to calculate diagram amplitudes using so-called Feynman rules, which can be derived from the system's underlying Lagrangian. Each internal line corres ...
See also:Feynman diagram, Feynman diagram - Motivation and history, Feynman diagram - Alternative names, Feynman diagram - Interpretation, Feynman diagram - Mathematical details, Feynman diagram - Examples, Feynman diagram - Beta decay, Feynman diagram - Quantum electrodynamics, Feynman diagram - Real φ4, Feynman diagram - Literature Read more here: » Feynman diagram: Encyclopedia II - Feynman diagram - Motivation and history |
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| | | | cross sections: Encyclopedia II - Hans Bethe - Biography Bethe was born in Strassburg (then part of Germany, now Strasbourg, France). He studied physics at Frankfurt and obtained his doctorate from the University of Munich with supervisor Arnold Sommerfeld, after which he did postdoctoral stints in Cambridge and at Enrico Fermi's laboratory in Rome. He left Germany in 1933 when the Nazis came to power and he lost his job (his mother was Jewish) at the University of Tubingen, moving first to England where he held a provisory position of Lecturer for the year 1933-1934 and in the fall of 1934, a fellowship at the University of Bristol. In England, Bethe worked with the theoretician Rudolf Peierls on ...
See also:Hans Bethe, Hans Bethe - Biography, Hans Bethe - Manhattan Project, Hans Bethe - Hydrogen bomb, Hans Bethe - Political stances, Hans Bethe - Awards and legacy, Hans Bethe - Honors Read more here: » Hans Bethe: Encyclopedia II - Hans Bethe - Biography |
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| | | | cross sections: Encyclopedia II - Computational chemistry - Ab initio methods The programs used in computational chemistry are based on many different quantum-chemical methods that solve the molecular Schrödinger equation associated with the molecular Hamiltonian. Methods that do not include empirical or semi-empirical parameters in their equations - are derived directly from theoretical principles, with no inclusion of experimental data - are generally called ab initio methods. Most of the time this is referring to approximate quantum mechanical calculations. The approximations made in these cases, however, a ...
See also:Computational chemistry, Computational chemistry - Introduction, Computational chemistry - Ab initio methods, Computational chemistry - Electronic structure, Computational chemistry - Chemical dynamics, Computational chemistry - Semiempirical methods, Computational chemistry - Electronic structure, Computational chemistry - Molecular mechanics, Computational chemistry - Software packages Read more here: » Computational chemistry: Encyclopedia II - Computational chemistry - Ab initio methods |
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| | | | cross sections: Encyclopedia II - Prompt neutron - Principle We will use U-235 as an example. The immediate mass products of a fission event are two large fission fragments, which are remnants of the original U-235 nucleus, plus, on average, two or three free neutrons (in average 2.47), called "prompt" neutrons. Later, a fission fragment occasionally, but rarely, undergoes a stage of radioactive decay that yields an additional neutron, called a "delayed" neutron. These neutron-emitting fission fragments ...
See also:Prompt neutron, Prompt neutron - Principle, Prompt neutron - Importance in nuclear reactors, Prompt neutron - Fraction definitions Read more here: » Prompt neutron: Encyclopedia II - Prompt neutron - Principle |
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| | | | cross sections: Encyclopedia II - Aneutronic fusion - Residual radiation from a p-11B reactor For the above reasons, most advocates of aneutronic fusion concentrate on the last reaction, p-11B. Even here, though, there are a number of side reactions that will produce neutrons or other radiation, among them the following:
as well as reactions with a possible 10B impurity fraction. Detailed calculations (Heindler and Kernbichler, Proc. 5th Intl. Conf. on Emerging Nuclear Energy Systems, 1989, pp. 177-82) show that at least 0.1% of the reactions in a thermal p-11B plasma would produce neutrons. This i ...
See also:Aneutronic fusion, Aneutronic fusion - Candidate aneutronic reactions, Aneutronic fusion - Residual radiation from a p-11B reactor, Aneutronic fusion - Power density and energy balance Read more here: » Aneutronic fusion: Encyclopedia II - Aneutronic fusion - Residual radiation from a p-11B reactor |
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| | | | cross sections: Encyclopedia II - Asymptotic freedom - Discovery The fact that asymptotic freedom is a feature of quantum chromodynamics (QCD), the quantum field theory of the interactions of quarks and gluons, was discovered by David Gross, Frank Wilczek, and David Politzer in 1973. For their discovery, Gross, Wilczek and Politzer were awarded the Nobel Prize in Physics in 2004.
Asymptotic freedom implies that in high-energy scattering the quarks move within nucleons, such as the neutron and proton, essentially as free, non-interacting particles, and it allows physicists to calculate the cross sections of various events in pa ...
See also:Asymptotic freedom, Asymptotic freedom - Discovery, Asymptotic freedom - Screening and antiscreening, Asymptotic freedom - Calculating asymptotic freedom, Asymptotic freedom - External link Read more here: » Asymptotic freedom: Encyclopedia II - Asymptotic freedom - Discovery |
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| | | | cross sections: Encyclopedia II - Computational chemistry - Introduction The term theoretical chemistry may be defined as a mathematical description of chemistry, whereas computational chemistry is usually used when a mathematical method is sufficiently well developed that it can be automated for implementation on a computer. Note that the words exact and perfect do not appear here, as very few aspects of chemistry can be computed exactly. Almost every aspect of chemistry, however, can be and has been described in a quali ...
See also:Computational chemistry, Computational chemistry - Introduction, Computational chemistry - Ab initio methods, Computational chemistry - Electronic structure, Computational chemistry - Chemical dynamics, Computational chemistry - Semiempirical methods, Computational chemistry - Electronic structure, Computational chemistry - Molecular mechanics, Computational chemistry - Software packages Read more here: » Computational chemistry: Encyclopedia II - Computational chemistry - Introduction |
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