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Neodymium - Promethium - Samarium
Name, Symbol, NumberPromethium, Pm, 61
Chemical series Lanthanides
Group, Period, Block_ [?], 6 , f
Density, Hardness 7264 kg/m3, no data
Appearance metallic
Atomic properties
Atomic weight 145 amu
Atomic radius (calc.) 185 (205) pm
Covalent radius no data
van der Waals radius no data
Electron configuration [Xe]6s²4f5
e- 's per energy level2, 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 ×10-3 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
isoNAhalf-life DMDE MeVDP
145Pm{syn.}x17.7 yε0.163145Nd
146Pm{syn.}5.53 yε1.472146Nd
147Pm{syn.}2.6234 yβ-0.224147Sm
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.

Table of contents

Notable characteristics

Promethium is a soft beta emitter; it does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays. Little is known as of today about the properties of metallic promethium; two allotropic modifications exist, and 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 gages.
  • 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 5 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 Branner in 1902; this prediction was confirmed by 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 1944 only 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 2, they did not claim their discovery until 1946. The name Promethium is derived from Prometheus from 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 g 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 146-Nd with neutrons, turning it into 147-Nd which decays into 147-Pm through beta decay with a half-life of 11 days.

Biological role

Promethium has no biological role.


Promethium does not naturally occur on earth, but has been identified in the spectrum of the star HR465[?] in Andromeda.


Promethium compounds include:


36 radioisotopes of Promethium have been characterized, with the most stable being 145-Pm with a half-life of 17.7 years, 146-Pm with a half-life of 5.53 years, and 147-Pm with a half-life of 2.6234 years. All of the remaining radioactive isotopes have half-lifes that are less than 364 days, and the majority of these have half lifes that are less than 27 seconds. This element also has 11 meta states with the most stable being 148m-Pm (t 41.29 days), 152m2-Pm (t 13.8 minutes) and 152m-Pm (t 7.52 minutes).

The isotopes of Promethium range in atomic weight from 127.9482600 amu (128-Pm) to 162.9535200 amu (163-Pm). The primary decay mode before the most abundant stable isotope, 145-Pm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 145-Pm are element Nd (Neodymium) isotopes and the primary products after are element Sm (Samarium) isotopes.


Great care is required while handling promethium as a consequence of its high radioactivity; in particular, Promethium can emit X-rays during its beta decay.

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