Promethium (Pm)

Promethium is a radioactive metal with atomic number 61, belonging to the lanthanide series. This element does not occur naturally or is found only in trace amounts; it was definitively identified and synthesized artificially in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell. Its name is derived from Prometheus of Greek mythology, and it is primarily used in nuclear batteries and luminescent paints.

Classification and Basic Properties

Promethium (Pm) is an element located in the sixth period of the periodic table within the lanthanide group. Its electron configuration is [Xe] 4f⁵6s². Among all elements in the lanthanide series, promethium is the only one with no stable isotopes; all its isotopes are radioactive. It exhibits metallic properties and is expected to be solid at room temperature. Its density is estimated at approximately 7.26 g/cm³.

Discovery

The existence of promethium had long been suspected due to its position in the periodic table between neodymium and samarium. In 1902, Czech chemist Bohuslav Brauner proposed that an element must exist in this gap. In the early 20th century, various researchers claimed to have discovered the element, such as B.S. Hopkins and colleagues who named it “illinium,” and Luigi Rolla and associates who called it “florentium”; however, these claims were never confirmed.

The definitive identification and isolation of promethium was achieved in 1945 (some sources cite 1947) at the Oak Ridge National Laboratory in the United States by Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell. The team detected promethium while separating fission products of uranium using ion-exchange chromatography.

Promethium (Generated by Artificial Intelligence.)

Etimology

The name promethium was proposed by Grace Mary Coryell, wife of Charles D. Coryell. It honors Prometheus, the Titan from Greek mythology who stole fire from the gods and gave it to humanity, for which he was punished. This naming symbolizes both the element’s production through nuclear “fire” (reactors) and the challenges and potential power associated with its discovery. The name was officially accepted by the International Union of Pure and Applied Chemistry (IUPAC) in 1949.

Natural Occurrence

Promethium is found in nature in negligible quantities. It is estimated that at any given time, only about 500 to 600 grams of promethium exist naturally in the Earth’s crust. This trace amount arises from the spontaneous fission of uranium in ores or from the rare neutron capture reaction of europium-151.

The detection of promethium in a star in the Andromeda Galaxy suggests that it may also form through nucleosynthesis processes in stars, although this process is not yet fully understood. Commercially and research-grade promethium is produced entirely artificially, typically as a byproduct of uranium, thorium, or plutonium fission in nuclear reactors or by neutron bombardment of lighter elements such as neodymium.

Promethium in a Laboratory Environment (Generated by Artificial Intelligence.)

Physical and Chemical Properties

Due to its radioactivity, direct observational data on promethium in its metallic form are extremely limited. Current knowledge is largely based on theoretical calculations and comparisons with other lanthanide elements. It is presumed to be a silvery-white metal that is solid at room temperature. Its melting point is estimated at approximately 1042 °C, though some sources suggest it may reach up to 1160 °C.

The boiling point is estimated at approximately 3000 °C. Its density is around 7.26 g/cm³, and its atomic radius is calculated to be approximately 238 picometers. Chemically, promethium is expected to exhibit reactivity similar to other lanthanides and typically assumes a +3 oxidation state in its compounds. More than 30 promethium compounds have been synthesized to date.

Isotopes

All isotopes of promethium are radioactive. More than 30 isotopes are known. The most stable and longest-lived isotope is promethium-145 (¹⁴⁵Pm), with a half-life of approximately 17.7 years. However, the most widely used and practically valuable isotope is promethium-147 (¹⁴⁷Pm).

• ¹⁴⁵Pm: Half-life ~17.7 years. Decays by electron capture to neodymium-145.
• ¹⁴⁷Pm: Half-life of 2.6234 years. Decays via beta-minus (β⁻) emission to samarium-147. Produced in nuclear reactors and used in various applications. TÜBİTAK sources list ¹⁴⁵Pm and ¹⁴⁷Pm as important isotopes. Other isotopes such as Pm-143 (265 years) and Pm-144 (360 years) are listed in Wikipedia, but these values may not be consistent with other sources, and ¹⁴⁵Pm is generally accepted as the most stable isotope.

Applications

The radioactive properties of promethium enable its use in specialized applications:

• Nuclear Batteries (Atomic Batteries): Promethium-147 generates energy by emitting beta particles. This energy can excite a phosphorescent material to produce light, which is then converted into electricity by a photovoltaic cell (solar cell), creating long-lasting (several years) nuclear batteries. These miniature batteries, sometimes the size of a pin, have been or are used in cardiac pacemakers, guided missiles, spacecraft, satellites as auxiliary heat and power sources, radioluminescent devices, and other portable equipment. Some sources indicate they can operate for up to five years under extreme temperatures.
• Luminescent Paints: ¹⁴⁷Pm has been used as a substitute for tritium in luminescent paints that emit continuous light through beta particle excitation of phosphors. These paints are used on clock faces, instrument panels, and emergency exit signs. The emitted light is considered harmless.
• Thickness Gauges: Beta particles emitted by ¹⁴⁷Pm serve as a radiation source in industrial measuring devices used to determine the thickness of thin materials such as paper, plastic film, and metal sheets.
• X-ray Source: When mixed with heavy atomic elements, promethium can produce X-rays, a property exploited in portable X-ray sources. It is also used as a radiation source in measurement instruments.
• Scientific Research: Promethium and its isotopes are used in fundamental scientific research in nuclear physics and chemistry.

Biological Role and Precautions

Promethium has no known biological role. All promethium isotopes are radioactive, making promethium and its compounds hazardous to living organisms. Beta emitters such as ¹⁴⁷Pm can cause damage to tissues and organs when internalized through ingestion or inhalation, increasing the risk of cancer. Therefore, strict radiation safety protocols must be followed when handling promethium. Special protective equipment, ventilated and shielded work areas such as glove boxes should be used, and contamination must be strictly prevented. It must be handled with extreme care.