Samarium
Samarium is a chemical element, a very hard, silvery
white metal of the lanthanide series in Group IIIB on the
periodic table. Its symbol is Sm; its atomic number, 62;
and its atomic weight, 150.4 (average weight of its seven
natural isotopes). Three natural samarium isotopes are
radioactive. Samarium was discovered in 1879 by Lecoq de
Boisbaudran, who isolated it from samarskite. The metal
ignites in air at 150 deg C (302 deg F). Because one of
its isotopes has a high cross section of neutron
absorption, samarium is used in the control rods of nuclear
reactors. An alloy of samarium with cobalt is used to make
a magnetic material with the highest resistance to
demagnetization of any known material.