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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 ...
The "Six-factor formula" is the neutron life-cycle balance equation, which includes six separate factors, the product of which is equal to the ratio of the number of neutrons in any generation to that of the previous one; this parameter is called the effective multiplication factor k, also denoted by K eff, where k = Є L f ρ L th f η, where ...
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 ...
Defining equation SI units Dimension Number of atoms N = Number of atoms remaining at time t. N 0 = Initial number of atoms at time t = 0 N D = Number of atoms decayed at time t = + dimensionless dimensionless Decay rate, activity of a radioisotope: A = Bq = Hz = s −1 [T] −1: Decay constant: λ
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 effect of absorption in some 238 U nuclei on absorption in others is called resonance level shielding. It increases with increasing concentration of resonance absorbers. As an example, we can calculate the effective resonance integral in a homogeneous natural uranium-graphite mixture with the ratio N 3 /N 8 =215.
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 ...
Additionally, there is also a shielding effect that occurs between sublevels within the same principal energy level. An electron in the s-sublevel is capable of shielding electrons in the p-sublevel of the same principal energy level. The size of the shielding effect is difficult to calculate precisely due to effects from quantum mechanics.