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Regardless of whether the upward incident beam is shaped like a circle, square or rectangle, specific calculation formalism has been described. [ 5 ] [ 6 ] The intensity of radiation measured at the surface immediately surrounding the facility increases with growing distance from the shielding barrier to reach a maximum and then fall again ...
A fixed source calculation involves imposing a known neutron source on a medium and determining the resulting neutron distribution throughout the problem. This type of problem is particularly useful for shielding calculations, where a designer would like to minimize the neutron dose outside of a shield while using the least amount of shielding ...
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 ...
The code was finalized in December 1947. The first calculations were run in April/May 1948 on ENIAC. While waiting for ENIAC to be physically relocated, Enrico Fermi invented a mechanical device called FERMIAC [7] to trace neutron movements through fissionable materials by the Monte Carlo method. Monte Carlo methods for particle transport have ...
The mere fact that an assembly is supercritical does not guarantee that it contains any free neutrons at all. At least one neutron is required to "strike" a chain reaction, and if the spontaneous fission rate is sufficiently low it may take a long time (in 235 U reactors, as long as many minutes) before a chance neutron encounter starts a chain reaction even if the reactor is supercritical.
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).
Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay: [2] n 0 → p + + e − + ν e. Although the p + and e − produced by neutron decay are detectable, the decay rate is too low to serve as the basis for a practical detector system.
The inner 238 U nuclei are shielded by the surface nuclei and participate less in the resonant neutron absorption, and the shielding increases with the increase of the fuel element diameter d. Therefore, the effective 238 U resonance integral in a heterogeneous reactor depends on the fuel element diameter d :