(So named (Greek Prometheus) in 1949 for earlier prometheum, a name proposed by G. M. Coryell) A radioactive chemical element, one of the rare-earth metals isolated in 1948 by J. A. Marinsky and L. E. Glendenin, U.S. physicists. It is obtained from fission of uranium or neutron bombardment of neodymium and used in phosphorescent paint, as a power source, X-ray source, etc.

Symbol: Pm
Atomic number: 61
Atomic weight: 145 (isotope with the longest known half-life)
Density (at room temperature and pressure): 7.26 g/cc
Melting point: 1,100°C
Boiling point: 3,000°C
Main valence: +3
Ground state electron configuration: [Xe]4f56s2