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Name, Symbol, Number Promethium, Pm, 61
Chemical series Lanthanides
Group, Period, Block _ , 6, f
Density, Hardness 7264 kg/m3, no data
Appearance metallic
Atomic properties
Atomic weight 145 u
Atomic radius (calc.) 185 (205) pm
Covalent radius no data
van der Waals radius no data
Electron configuration [Xe]6s²4f5
e- 's per energy level 2, 8, 18, 23,8, 2
Oxidation states (Oxide) 3 (mildly basic)
Crystal structure Hexagonal
Physical properties
State of matter solid (__)
Melting point 1373 K (2012 ?F)
Boiling point 3273 K (5432 ?F)
Molar volume 20.23 ×10-6 m3/mol
Heat of vaporization no data
Heat of fusion 86.7 kJ/mol
Vapor pressure no data
Velocity of sound no data
Electronegativity 1.13 (Pauling scale)
Specific heat capacity 180 J/(kg*K)
Electrical conductivity no data
Thermal conductivity 17.9 W/(m*K)
1st ionization potential 540 kJ/mol
2nd ionization potential 1050 kJ/mol
3rd ionization potential 2150 kJ/mol
4th ionization potential 3970 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP
145Pm {syn.}x 17.7 y ε 0.163 145Nd
146Pm {syn.} 5.53 y ε 1.472 146Nd
β- 1.542 146Sm
147Pm {syn.} 2.6234 y β- 0.224 147Sm
SI units & STP are used except where noted.

Promethium is a chemical element in the periodic table that has the symbol Pm and atomic number 61.

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Notable characteristics

Promethium has no stable isotopes. It is a man-made soft beta emitter; it does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays. Pure promethium exists in two allotropic forms, but little else is known about the metal. Promethium salts luminesce in the dark with a pale blue or greenish glow due to their high radioactivity.


Uses for promethium include:

  • Beta radiation source for thickness gauges.
  • Light source for signals that require dependable operation (using phosphor to absorb the beta radiation and produce light).
  • In a nuclear battery in which photocells convert the light into electric current, yielding a useful life of about five years using 147-Pm.
  • Possibly in the future as a portable X-ray source, as an auxiliary heat / power source for space probes and satellites, and to make lasers that can be used to communicate with submerged submarines.


The existence of promethium was first predicted by Bohuslav Brauner in 1902; this prediction was confirmed by Henry Moseley in 1914. Several groups claimed to have produced the element, but they could not confirm their discoveries because of the difficulty of separating promethium from other elements. Proof of the existence of promethium was obtained in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell during the analysis of byproducts of uranium fission; however, being too busy with defense-related research during World War II, they did not announce their discovery until 1947. [1] ( The name promethium is derived from Prometheus in Greek mythology, who stole the fire of the sky and gave it to mankind.

In 1963, ion-exchange methods were used to prepare about 10 grams of promethium from atomic reactor fuel processing wastes.

Today, promethium is still recovered from the byproducts of uranium fission; it can also be produced by bombarding 146Nd with neutrons, turning it into 147Nd which decays into 147Pm through beta decay with a half-life of 11 days.

Promethium is also the name of a fictional element in the DC Universe; writer Marv Wolfman has admitted having been unaware of the existence of a real substance by that name at the time he wrote the original script featuring the name.

A substance called promethium is also used in the war game Warhammer 40,000. It is a fictional napalm-like flammable material.


Promethium does not naturally occur on earth, but has been identified in the spectrum of the star HR 465 in Andromeda, and possibly HD 101065 (Przybylski's star) and HD 965 [2] (


Promethium compounds include:


36 radioisotopes of promethium have been characterized, with the most stable being 145Pm with a half-life of 17.7 years, 146Pm with a half-life of 5.53 years, and 147Pm with a half-life of 2.6234 years. All of the remaining radioactive isotopes have half-lives that are less than 364 days, and the majority of these have half lives that are less than 27 seconds. This element also has 11 meta states with the most stable being 148Pmm (T? 41.29 days), 152Pmm2 (T? 13.8 minutes) and 152Pmm (T? 7.52 minutes).

The isotopes of promethium range in atomic weight from 127.9482600 u (128Pm) to 162.9535200 u (163Pm). The primary decay mode before the longest-lived isotope, 145Pm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 145Pm are neodymium (Nd) isotopes and the primary products after are samarium (Sm) isotopes.


Promethium must be handled with great care because of its high radioactivity. In particular, promethium can emit X-rays during its beta decay. Note that its half-life is less than that of plutonium-239 by a factor of multiple thousands to tens of thousands. Promethium has no biological role.



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