LEN, or Low Energy Neutron, refers to a type of neutron that has a lower kinetic energy compared to thermal neutrons. These neutrons are important in various fields, including nuclear physics and materials science, as they can penetrate materials more effectively without causing significant damage. In nuclear reactors, LEN can be used to initiate and sustain nuclear reactions. They play a crucial role in neutron scattering experiments, helping scientists study the structure and properties of materials at the atomic level. Understanding LEN is essential for advancements in both energy production and material research.