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A thermal neutron is a free neutron with a kinetic energy of about 0.025 eV (about 4.0×10 −21 J or 2.4 MJ/kg, hence a speed of 2.19 km/s), which is the energy corresponding to the most probable speed at a temperature of 290 K (17 °C or 62 °F), the mode of the Maxwell–Boltzmann distribution for this temperature, E peak = k T.
Neutron moderators are used to produce thermal neutrons, which have kinetic energies below 1 eV (T < 500K). [1] Thermal neutrons are used to maintain a nuclear chain reaction in a nuclear reactor, and as a research tool in neutron scattering experiments and other applications of neutron science (see below). The remainder of this article ...
A neutron's energy can vary widely, but it is not uncommon to have energies up to and exceeding 10 MeV (10,000,000 eV) in the centre of a nuclear reactor. A neutron with a significant amount of energy will create a displacement cascade in a matrix via elastic collisions. For example, a 1 MeV neutron striking graphite will create 900 ...
In many substances, thermal neutron reactions show a much larger effective cross-section than reactions involving faster neutrons, and thermal neutrons can therefore be absorbed more readily (i.e., with higher probability) by any atomic nuclei that they collide with, creating a heavier – and often unstable – isotope of the chemical element ...
In physics, thermalisation (or thermalization) is the process of physical bodies reaching thermal equilibrium through mutual interaction. In general, the natural tendency of a system is towards a state of equipartition of energy and uniform temperature that maximizes the system's entropy.
Neutron transport (also known as neutronics) is the study of the motions and interactions of neutrons with materials. Nuclear scientists and engineers often need to know where neutrons are in an apparatus, in what direction they are going, and how quickly they are moving.
These thermal neutrons are immensely more susceptible than fast neutrons to propagate a nuclear chain reaction of uranium-235 or other fissile isotope by colliding with their atomic nucleus. Water (sometimes called "light water" in this context) is the most commonly used moderator (roughly 75% of the world's reactors).
The symbols are defined as: [3], and are the average number of neutrons produced per fission in the medium (2.43 for uranium-235). and are the microscopic fission and absorption thermal cross sections for fuel, respectively.