Promethium (Pm)
Isotopes of Promethium
| Isotope | Atomic Mass | Half-life | Mode of Decay | Nuclear Spin | Nuclear Magnetic Moment |
| Pm-143 | 142.910928 | 265 days | EC to Nd-143 | 5/2 | 3.8 |
| Pm-144 | 143.912586 | 360 days | EC to Nd-144 | 5 | 1.7 |
| Pm-145 | 144.912743 | 17.70 years | EC to Nd-145; α to Pr-141 |
5/2 | No data available |
| Pm-146 | 145.914693 | 5.53 years | EC to Nd-146; β- to Sm-146 |
3 | No data available |
| Pm-147 | 146.915134 | 2.6234 years | β- to Sm-147 | 7/2 | 2.6 |
| Pm-148 | 147.91747 | 5.37 days | β- to Sm-148 | 1 | 2.0 |
| Pm-149 | 148.918330 | 2.212 days | β- to Sm-149 | 7/2 | 3.3 |
| Pm-150 | 149.92098 | 2.68 hours | β- to Sm-150 | 1 | No data available |
| Pm-151 | 150.92120 | 1.183 days | β- to Sm-151 | 5/2 | 1.8 |
Promethium was first produced and characterized at Oak Ridge National Laboratory (then Clinton Laboratories), Oak Ridge, Tennessee, USA, in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell. Its name was originally spelled “prometheum” (and was subsequently changed to its current spelling), referring to Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans.
Promethium is a silvery-white metal that does not occur in metallic form in nature. Minute quantities are associated with other rare earths. Because of its radioactivity, the metal and its salts luminesce in the dark, giving a pale blue or greenish glow. It is insoluble in water. It forms all of its compounds in a +3 oxidation state — several compounds have been prepared and are well characterized.
Promethium has very limited applications. It is used in phosphor lights to produce signals. It is also used as a beta particle source for thickness gauges, nuclear batteries and portable x-ray units. All isotopes of promethium, along with their salts, present a radiation hazard from exposure to beta and gamma rays.
Properties of Promethium
| Name | Promethium |
| Symbol | Pm |
| Atomic number | 61 |
| Atomic weight | 145 |
| Standard state | Solid at 298 °K |
| CAS Registry ID | 7440-12-2 |
| Group in periodic table | N/A |
| Group name | Lanthanoid |
| Period in periodic table | 6 (Lanthanoid) |
| Block in periodic table | f-block |
| Color | Metallic |
| Classification | Metallic |
| Melting point | 1100 °C |
| Boiling point | 3000 °C |
| Vaporization point | 2460 ºC |
| Thermal conductivity | 15 W/(m·K) |
| Electrical resistivity | About 75 x 10-8 Ω·cm |
| Heat of vaporization | 290 kJ·mol-1 |
| Heat of fusion | About 7.7 kJ·mol-1 |
| Density of solid | 7.26 g/cm3 |
| Electron configuration | [Xe]4f56s2 |
| Ionic radius | Pm3+: 0.98 Å |
| Oxidation state | +3 |
