A thermal neutron is a type of neutron that has low kinetic energy, typically around 0.025 electron volts (eV). These neutrons are in thermal equilibrium with their surrounding environment, meaning they have similar energy levels to the molecules in that environment. Thermal neutrons are important in nuclear reactions, particularly in nuclear reactors, where they can effectively induce fission in certain isotopes like uranium-235. Thermal neutrons are produced when fast neutrons lose energy through collisions with materials, such as hydrogen in water or other light elements. This process is crucial for sustaining a controlled nuclear chain reaction. Their ability to be easily absorbed by certain nuclei makes thermal neutrons valuable in various applications, including neutron activation analysis and radiotherapy.