Samarium was first detected in 1879 by the French chemist Paul-Emile Lecoq de Boisbaudran, in the mineral samarskite. He named it after the mineral, which in turn had been named for Vasili Samarsky-Bykhovets, a Russian mining official who had granted access to the ore. Samarium is a moderately hard, silvery rare-earth metal, valued for samarium-cobalt magnets that keep their strength at high temperatures and for its use in cancer treatment. Such magnets hold their power where others fail in heat, suiting them to aircraft and military hardware, and samarium also serves as a neutron absorber in reactors, as a catalyst, and, as a radioactive isotope, in the relief of cancer pain.
In reactor physics samarium-149, a stable fission product, behaves as a neutron poison much like the more famous xenon-135, gradually building up in a reactor's fuel and absorbing neutrons that would otherwise sustain the chain reaction, a slow-acting effect engineers must account for over a reactor's operating life quite separately from samarium's own deliberate use as a shielding and control material. Samarium-153, a different radioactive isotope of the same element, is injected directly into patients as a targeted treatment that relieves pain from cancer that has spread to bone.