A neutron absorber is a material that can capture and reduce the number of neutrons in a nuclear reaction. These materials are essential in controlling nuclear fission processes, such as those occurring in nuclear reactors. By absorbing neutrons, they help maintain a stable reaction rate and prevent overheating. Common examples of neutron absorbers include substances like boron and cadmium. These elements are often used in control rods, which are inserted into the reactor core to manage the fission process. By adjusting the position of these rods, operators can effectively control the energy output of the reactor.