Promethium is a radioactive lanthanide metal with no stable isotopes. It is silvery, forms a +3 oxidation state, and is used in luminous paints and as a beta source.
Promethium (Pm) is the only lanthanide with no stable isotopes. All its isotopes are radioactive, with 145Pm (half-life ≈ 17.7 years) and 147Pm (half-life ≈ 2.62 years) being the most commonly encountered. Its absence of stable nuclides makes it extremely rare in nature.
Promethium was first identified in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell during the Manhattan Project. It was discovered as a fission product of uranium in nuclear reactor fuel. Later, it was named after the Greek Titan Prometheus, who stole fire from the gods.
Only trace amounts of Promethium occur naturally in uranium ores (via spontaneous fission) and from cosmic ray spallation. Estimates suggest less than one part per trillion in Earth's crust. Most samples are produced synthetically from nuclear reactors or decay of other isotopes such as 147Nd.
The ground-state configuration is [Xe] 4f5 6s2. It typically forms Pm3+ ions by losing the two 6s electrons and one 4f electron, resulting in a 4f4 configuration in compounds.
Promethium almost exclusively exhibits the +3 oxidation state, similar to most lanthanides. The Pm3+ ion forms salts and oxides such as Pm2O3 and PmCl3.
Promethium’s beta radiation (from isotopes like 147Pm) makes it useful in:
Promethium isotopes are primarily obtained from fission of uranium-235 in nuclear reactors or by neutron irradiation of neodymium:
\(\mathrm{^{146}Nd + n \rightarrow ^{147}Nd \xrightarrow[\beta^-]{11\,d} ^{147}Pm}\)
The Pm is separated from the irradiated fuel through complex chemical extraction processes.
Yes. All Promethium isotopes are radioactive. Although it primarily emits beta particles (which can be shielded with glass or plastic), internal exposure through inhalation or ingestion is hazardous. Handling requires remote tools, protective barriers, and controlled laboratory environments.
Promethium(III) compounds are typically pale pink to violet in color. The color arises from f–f transitions within the 4f orbitals of Pm3+, similar to other trivalent lanthanide ions.
Like other reactive lanthanides, Promethium reacts readily with oxygen to form its sesquioxide:
\(\mathrm{4\,Pm(s) + 3\,O_2(g) \rightarrow 2\,Pm_2O_3(s)}\)
The oxide is stable, non-volatile, and exhibits the typical +3 oxidation state of Pm.
Promethium-147 emits low-energy beta particles that can be converted into electricity in betavoltaic cells or used to heat thermoelectric materials in RTGs. These batteries power instruments in space probes and remote sensing equipment.
Not anymore. Due to radioactivity concerns, Promethium-based luminous paints have been replaced by safer phosphorescent materials like tritium gas or photoluminescent pigments. Its modern applications are confined to scientific, industrial, and aerospace uses.