Promethium (Pm)

Soft silvery metallic element, belongs to the lanthanoids. Pm-147, the only natural isotope, is radioactive and has a half-life of 252 years. Eighteen radioisotopes have been produced, but all have very short half-lives. Found only in nuclear decay waste. Pm-147 is of interest as a beta-decay source, however Pm-146 and Pm-148 have to be removed from it first, as they generate gamma radiation. Discovered by J.A. Marinsky, L.E. Glendenin and C.D. Coryell in 1947.
Atomic Number61
Atomic Weight144.91276
Mass Number126
Protons61 p+
Neutrons65 n0
Electrons61 e-
Promethium.jpg Animated Bohr Model Enhanced Bohr Model Bohr Model Orbital Diagram


Atomic Radius
185 pm
Atomic Volume
Covalent Radius
173 pm
Metallic Radius
Ionic Radius
97 pm
Crystal Radius
111.00000000000001 pm
Van der Waals radius
238 pm
7.26 g/cm³
Boiling Point
3,000 K
Melting Point
1,441 K
Electrons per shell2, 8, 18, 23, 8, 2
Proton Affinity
Electron Affinity
Ionization Potential
Heat of Vaporization
Heat of Fusion
Heat of Formation
Molar Heat Capacity
Specific Heat Capacity
Thermal Conductivity
17.9 W/(m K)
Gas Basicity
Dipole Polarizability
200 a₀
C6 Dispersion Coefficient
Oxidation States3
Crystal Structure ()
Lattice Constant
Bulk Modulus
Electrical Resistivity
Electron Configuration[Xe] 4f5 6s2
Magnetic Ordering
Magnetic Susceptibility
Poisson Ratio
Shear Modulus
Young's Modulus
Alternate Names
Adiabatic Index
Electric Conductivity
Critical Pressure
Critical Temperature
Curie Point
Magnetic Susceptibility
Neel Point
Neutron Cross Section
Neutron Mass Absorption
Gas Phase
Quantum Numbers
Refractive Index
Space Group
Speed of Sound
Superconducting Point
Thermal Expansion
Valence Electrons
CategoryLanthanides, Lanthanides
CAS Group
Glawe Number28
Mendeleev Number21
Pettifor Number29
Geochemical Classrare earth & related
Goldschmidt Classlitophile
RadioactiveYes ☢️
Decay Mode
Abundance in Earth's crust
Abundance in Oceans
Abundance in Human Body
Abundance in Meteor
Abundance in Sun
Abundance in Universena

Isotopes of Promethium

Stable Isotopes
Unstable Isotopes
126Pm 127Pm 128Pm 129Pm 130Pm 131Pm 132Pm 133Pm 134Pm 135Pm 136Pm 137Pm 138Pm 139Pm 140Pm 141Pm 142Pm 143Pm 144Pm 145Pm 146Pm 147Pm 148Pm 149Pm 150Pm 151Pm 152Pm 153Pm 154Pm 155Pm 156Pm 157Pm 158Pm 159Pm 160Pm 161Pm 162Pm 163Pm


The existence of an element between neodymium and samarium was first predicted by Czech chemist Bohuslav Brauner in 1902. Promethium was first produced and characterized at Oak Ridge National Laboratory in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell. It was produced by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. Named after the Greek Prometheus, who, according to mythology, stole fire from heaven

DiscoverersJ.A. Marinsky, L.E. Glendenin, C.D. Coryell
Discovery LocationUnited States
Discovery Year1945
Name OriginNamed for the Greek god, Prometheus.
Promethium is harmful due to its radioactivity
Promethium is the only lanthanide that has no stable isotopes


Promethium is also used in atomic batteries for spacecraft and guided missiles. Promethium is also used to measure the thickness of materials by evaluating the amount of radiation from a promethium source that passes through the sample. It has possible future uses in portable X-ray sources, and as auxiliary heat or power sources for space probes and satellites. It has been used as a source of radioactivity for thickness-measuring gages.


Does not occur naturally. Found among fission products of uranium, thorium, and plutonium.