Gadolinium. (Source: © Björn Wylezich / stock.adobe.com)

A chemical element with atomic number 64. Gadolinium is a silvery-white rare-earth metal. It is used in the nuclear industry for its ability to absorb neutrons. It can be used as neutron shielding or as an absorber as part of control rods. Gadolinium is sometimes added to nuclear fuel where it serves as a reactor burnable poison. The presence of an absorber slows the fission of fresh fuel. However, gadolinium is gradually converted by neutron capture into elements with low neutron absorption capacity. As the amount of usable fissile material decreases, the amount of absorber also decreases, and the fuel utilization becomes more uniform over the lifetime of the fuel in the reactor.