Name: Promethium
Symbol: Pm
Atomic Number: 61
Atomic Weight: 145.000000
Family: Rare Earth Elements
CAS RN: 7440-12-2
Description: A radioactive rare earth metal, metallic in appearance.
State (25C): Solid
Oxidation states: +3

Molar Volume: 19.95 cm3/mole
Valence Electrons: 4f56s2

Boiling Point:  3785K, 3512C,  6354F
Melting Point:
1204K,  931C, 1708F
Electrons Energy Level: 2, 8, 18, 23, 8, 2
Isotopes: 38 + None Stable + 11 meta states
Heat of Vaporization: 289 kJ/mol
Heat of Fusion: 86.7kJ/mol
Density: 7.3g/cm3 @ 300K
Specific Heat: 0.18 J/gK
Atomic Radius: 2.62
Ionic Radius: 0.979
Electronegativity: 1.13 (Pauling), 1.07 (Allrod Rochow)

1s2 2s2p6 3s2p6d10 4s2p6d10f5 5s2p6 6s2


Promethium - (Prometheus, who, according to mythology, stole fire from heaven).   The existence of promethium was first predicted by Bohuslav Brauner in 1902; this prediction was supported by Henry Mosely in 1914, who developed an x-ray method for determining integer atomic numbers of elements and found a gap for a missing element which would have atomic number 61, but was unknown (however, Moseley of course had no sample of the element to verify this).

Historical claims for the discovery of element 61 create an interesting trail from around 1925 in Florence (suggested name: florentium) to America in 1926 (suggested name: illinium).  None of the claims, however, could be substantiated and today we know they were not simply a result of fleetingly small samples but rather poor work.

While spectral lines of promethium are evident in the light from some stars, it now seems apparent that no promethium is found in accessible areas of the earth--hence the difficulty in finding any.  Initial attempts at synthesis of element 61 in a cyclotron at Ohio State University in 1941 led to the suggested name cyclonium. But the recognized synthesis and identification finally came at Oak Ridge.

Promethium was first produced and proved to exist at Oak Ridge National Laboratory (ORNL) in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell by separation and analysis of the fission products of uranium fuel irradiated in the Graphite Reactor; however, being too busy with defense-related research during World War II, they did not announce their discovery until 1947.  They discovered promethium while analyzing the byproducts of uranium fission that were produced in a nuclear reactor located at Clinton Laboratories in Oak Ridge, Tennessee.  Today, Clinton Laboratories is known as Oak Ridge National Laboratory.  The name promethium is derived from Prometheus in Greek mythology, who stole the fire of the sky and gave it to mankind.  The name was suggested by Grace Mary Coryell, Charles Coryell's wife, who felt that they were stealing fire from the gods.

In 1963, ion-exchange methods were used at ORNL to prepare about 10 grams of promethium from nuclear 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 has been identified in the spectrum of the star HR 465 in Andromeda, and possibly HD 101065 (Przybylski's Star) and HD 965.  This element is being formed recently near the star's surface, for no known isotope of promethium has a half-life longer than 17.7 years.   145Pm has a specific activity of 940 Ci/g.   It is a soft beta emitter; although no gamma rays are emitted, X-radiation can be generated when beta particles impinge on elements of a high atomic number, and great care must be taken in handling it.  Promethium salts luminesce in the dark with a pale blue-or greenish glow, due to their high radioactivity.  Ion-exchange methods led to the preparation of about 10 g of promethium from atomic reactor fuel processing wastes in early 1963.  Little is yet generally known about the properties of metallic promethium.  Two allotropic modifications exist.

2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f5
5s2 5p6


Promethium has one semi-stable isotope, 145Pm, it 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.  Pure promethium exists in two allotropic forms, and its chemistry is similar to other lanthanides.  Promethium salts luminesce in the dark with a pale blue or greenish glow due to their high radioactivity.  Promethium can be found in traces in some uranium ores as a fission product.

Today, promethium is still recovered from the byproducts of uranium fission. It can also be produced by bombarding neodymium-146 with neutrons.   Neodymium-146 becomes neodymium-147 when it captures a neutron. Neodymium-147, with a half-life of 11 days, decays into 147Pm through beta decay.  Promethium does not occur naturally on earth, although it has been detected in the spectrum of a star in the constellation Andromeda.


The element has applications as a beta source for thickness gages, and it can be absorbed by a phosphor to produce light.  Light produced in this manner can be used for signs or signals that require dependable operation; it can be used as a nuclear-powered battery by capturing light in photocells which convert it into electric current.  Such a battery, using 147Pm, would have a useful life of about 5 years.  It is being used for fluorescent lighting starter sand coatings for self-luminous watch dials.  Promethium shows promise as a portable X-ray source, and it may become useful as a heat source to provide auxiliary power for space probes and satellites.  Other uses:

Promethium can be formed as a product of uranium fission. Only trace amounts can be found in naturally occurring ores: a sample of pitchblende has been found to contain promethium at a concentration of four parts per quintillion (1018) by mass.


More than 30 promethium compounds have been prepared.  Most are colored.  147Pm is available upon special order from the Idaho National Engineering, Laboratory, Idaho Falls, ID, or from the Westinghouse Hanford Co., Richland, WA. 

Chlorides Bromides Oxides
PmCl3 PmBr3 Pm2O3


38 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).  145Pm decays into neodymium-145 through electron capture.

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.


Beside technetium, promethium is one of the two elements with atom number less than 83 that solely has unstable isotopes, which is a rarely occurring effect of the liquid drop model and stabilities of neighbor element isotopes.

There are no significant commercial uses of the metal and so very little has been produced except for theoretical studies.

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isotopic mass (u)
126Pm 125.95752 ~0.5 seconds
127Pm 126.95163 ~1 seconds
128Pm 127.94842 1.0 seconds
129Pm 128.94316 ~3 seconds
130Pm 129.94045 2.6 seconds
131Pm 130.93587 6.3 seconds
132Pm 131.93375 6.2 seconds
133Pm 132.92978 15 seconds
133mPm   ~10 seconds
134Pm 133.92835 22 seconds
134mPm   ~5 seconds
135Pm 134.92488 49 seconds
135mPm   40 seconds
136Pm 135.92357 107 seconds
136mPm   47 seconds
137Pm 136.920479 ~2 minutes
137mPm   2.4 minutes
138Pm 137.919548 10 seconds
138mPm   3.24 minutes
139Pm 138.916804 4.15 minutes
140Pm 139.91604 9.2 seconds
140mPm   5.95 minutes
141Pm 140.913555 20.90 minutes
142Pm 141.912874 40.5 seconds
143Pm 142.910933 265 days
144Pm 143.912591 363 days
145Pm 144.912749 17.7 years
146Pm 145.914696 5.53 years
147Pm 146.9151385 2.6234 years
148Pm 147.917475 5.368 days
148mPm   41.29 days
149Pm 148.918334 53.08 hours
150Pm 149.920984 2.68 hours
151Pm 150.921207 28.40 hours
152Pm 151.923497 4.12 minutes
152m1Pm   7.52 minutes
152m2Pm   13.8 minutes
153Pm 152.924117 5.25 minutes
154Pm 153.92646 1.73 minutes
154mPm   2.68 minutes
155Pm 154.92810 41.5 seconds
156Pm 155.93106 26.70 seconds
157Pm 156.93304 10.56 seconds
158Pm 157.93656 4.8 seconds
159Pm 158.93897 1.47 seconds
160Pm 159.94299 ~2 seconds
161Pm 160.94586 ~700 ms
162Pm 161.95029 ~500 ms
163Pm 162.95368 ~200 ms


40px-Skull_and_crossbones.svg.jpg (1420 bytes) 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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Promethium Data


Atomic Structure

Atomic Radius (): 2.62
Atomic Volume cm3/mol : 22.39cm3/mol
Covalent Radius: 1.63
Crystal Structure: Hexagonal
Ionic Radius: 0.979

Chemical Properties

Electrochemical Equivalents: 1.8022g/amp-hr
Electron Work Function: unknown
Electronegativity: 1.13 (Pauling); 1.07 (Allrod Rochow)
Heat of Fusion: 86.7 kJ/mol
First Ionization Potential: 5.554
Second Ionization Potential: 10.903
Third Ionization Potential: 22.283
Valence Electron Potential: 44.1 -eV
Ionization Energy: 5.55 eV

Physical Properties

Atomic Mass Average: 145
Boiling Point: 3785K, 3512C,  6354F
Melting Point: 1315K, 1042C, 1908F
Heat of Vaporization: 289 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 16E-6
Electrical Conductivity: unknown
Thermal Conductivity: 0.179 W/cmK
Density: 7.3g/cm3 @ 300K
Enthalpy of Atomization: 310 kJ/mole @ 25C
Enthalpy of Fusion: 7.5 kJ/mole
Enthalpy of Vaporization: unknown
Molar Volume: 19.95 cm3/mole
Specific Heat: 0.185 J/g mol @ 20C
Vapor Pressure: unknown
Estimated Crustal Abundance: unknown
Estimated Oceanic Abundance: unknown