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

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