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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 ...
Cold, thermal, and hot neutron radiation is commonly employed in neutron scattering facilities for neutron diffraction, small-angle neutron scattering, and neutron reflectometry. Slow neutron matter waves exhibit properties similar to geometrical and wave optics of light, including reflection, refraction, diffraction, and interference. [ 125 ]
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 multiplication factor, k, is defined as (see nuclear chain reaction): k = number of neutrons in one generation / number of neutrons in preceding generation . If k is greater than 1, the chain reaction is supercritical, and the neutron population will grow exponentially.
If k is greater than 1, the chain reaction is supercritical, and the neutron population will grow exponentially. If k is less than 1, the chain reaction is subcritical, and the neutron population will exponentially decay. If k = 1, the chain reaction is critical and the neutron population will remain constant.
Since protons and neutrons are both baryons, the mass number A is identical with the baryon number B of the nucleus (and also of the whole atom or ion). The mass number is different for each isotope of a given chemical element, and the difference between the mass number and the atomic number Z gives the number of neutrons (N) in the nucleus: N ...
The difference between the neutron number and the atomic number is known as the neutron excess: D = N − Z = A − 2Z. Neutron number is not written explicitly in nuclide symbol notation, but can be inferred as it is the difference between the two left-hand numbers (atomic number and mass).
The number of neutrons produced per fission is multiplicatively modified by the dominant eigenvalue. The resulting value of this eigenvalue reflects the time dependence of the neutron density in a multiplying medium. k eff < 1, subcritical: the neutron density is decreasing as time passes; k eff = 1, critical: the neutron density remains ...