Neutronabsorbent

Neutron-absorbent, also known as a neutron absorber, is a material that captures neutrons from a surrounding neutron field, thereby reducing the neutron flux and affecting the rate of nuclear reactions or radiation exposure. Absorbers are characterized by a high neutron capture cross section for the relevant energy spectrum (thermal or fast neutrons) and by their physical and chemical stability in the operational environment.

Common materials include boron-10 enriched compounds such as boron carbide (B4C) and borated stainless steels, cadmium and cadmium alloys, hafnium and hafnium alloys, and gadolinium compounds (notably gadolinium oxide and gadolinium alloys). Lithium-6 containing materials are used in some detector and shielding applications due to their large capture cross section. In shielding, borated polymers and concrete doped with boron or cadmium are often employed to absorb neutrons while providing structural support.

Neutron absorbers are used in nuclear reactors to control reactivity through neutron poisoning, in shielding around reactors, spent-fuel storage, radiography facilities, and medical or research irradiation facilities. They may be incorporated into control rods, shields, or composite materials that combine absorbers with moderators or structural elements. Absorbers are designed to balance effective neutron capture with mechanical strength, thermal stability, and ease of manufacture.

Important considerations include the energy dependence of the cross section, potential activation to radioactive isotopes, and the generation of secondary gamma radiation after neutron capture. Material choice also affects reactivity worth, heat load, corrosion resistance, and long-term disposal options. In some cases, absorbers must be replaced or reprocessed to manage radiation exposure and material aging.

Research and development continue to optimize neutron-absorbing materials for improved performance, reduced activation, and compatibility with advanced reactor designs and shielding requirements.