What does the term "thermalization" refer to in neutron behavior?

The term "thermalization" in the context of neutron behavior refers to the process by which fast neutrons lose energy and slow down to thermal energies. This occurs primarily through interactions with materials, such as hydrogen atoms in water or other substances. When neutrons collide with these nuclei, they transfer some of their kinetic energy, progressively reducing their speed. As a result, the neutrons reach a point where their kinetic energy corresponds to that of thermal motion, which is generally in the range of a few electron volts (eV).

Thermalized neutrons are important in many nuclear applications because they are more likely to cause fission in certain materials, such as uranium-235. The ability to control or facilitate the thermalization of neutrons is a key aspect in the design and operation of nuclear reactors and various neutron detection technologies.