Promethium (Pm)


  • Symbol: Pm
  • Atomic Number: 61
  • Atomic Weight: [145] (All isotopes are radioactive)
  • Element Classification: Lanthanide
  • Discovered By: Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell
  • Discovery Date: 1945
  • Name Origin: Named after Prometheus, the Titan from Greek mythology who stole fire from the gods and gave it to humans
  • Density(g/cc): 7.26 (estimated)
  • Melting Point: 1042°C (estimated)
  • Boiling Point: 3000°C (estimated)
  • Appearance: Metallic, with a silvery-white luster (presumed)
  • Atomic Radius(pm): 183 (estimated)


Promethium was discovered in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell during their research on the fission products of uranium fuel irradiated in a nuclear reactor. The discovery was made at Oak Ridge National Laboratory in Tennessee, USA, as part of the Manhattan Project. The element was named after Prometheus, reflecting the power and potential dangers of nuclear technology, akin to the mythical Prometheus bringing fire to humanity.

Relation to Other Elements

Promethium is a member of the lanthanide series, which consists of 15 elements from lanthanum to lutetium, characterized by their similar chemical behaviors and electronic configurations. Promethium is unique among lanthanides because it is the only element in the series that does not have any stable isotopes; all its isotopes are radioactive. Its properties and chemistry are similar to those of other lanthanides, particularly neodymium and samarium, which lie adjacent to it in the periodic table.

Natural Occurrence

Promethium is extremely rare in nature due to its instability; all its isotopes are radioactive with relatively short half-lives. Trace amounts of promethium have been detected in uranium ores and in the Earth’s crust, resulting from the natural fission of uranium and neutron capture processes. However, most promethium is synthetically produced in nuclear reactors through neutron bombardment of neodymium and samarium targets.


Due to its radioactivity and scarcity, promethium’s applications are limited and specialized:

  • Nuclear Batteries: Promethium-147 is used in atomic batteries, where its beta decay is converted into electric power. These batteries can be used in applications requiring long-lasting, low-power sources, such as in space probes, pacemakers, and remote sensing devices.
  • Luminous Paint: Promethium is used in luminous paint for watches, instrument panels, and signage. It provides luminescence without the need for recharging by light, unlike phosphorescent materials.
  • Research: Promethium’s radioactivity makes it useful in certain research applications, including studying the properties of lanthanides and in nuclear physics experiments.

The discovery of promethium filled the last remaining gap in the lanthanide series of the periodic table. Although its uses are limited due to its radioactivity and the difficulty of obtaining significant quantities, promethium’s applications in nuclear batteries and luminous paints demonstrate the utility of even the most elusive elements.


Neodymium (Nd)

Samarium (Sm)