Material that absorbs neutrons through the neutron capture process. Typical best absorbers are boron, cadmium, gadolinium, hafnium, and cobalt. Neutron absorbers are used in fission reactors for the regulation of fission reactions or as a component of shielding from neutron radiation. For example, boron is typically used in the form of solid boron carbide or liquid boric acid in virtually all nuclear reactors. It is a component of control rods, shut-off rods, and is added to water during fuel handling in water-cooled reactors.