Introduction to Rare Earth Element Promethium

The radioactive rare earth promethium fascinates with its extreme rarity and instability. At most, only 500-600 grams exist naturally worldwide, dispersed in the earth's crust and constantly decaying. As all promethium isotopes are radioactive, the element is scarce yet perpetually regenerated through decay chains. This ephemeral element is the sole rare earth metal that is inherently radioactive. With no stable isotopes, promethium occurs only fleetingly via spontaneous fission and other decay processes. Tracking promethium reveals insights into the heart of nuclear reactivity governing Earth's deep interior. Though unsettled, this ephemeral element's origins and behavior still intrigue researchers.

The rare earth metal promethium, named for the Greek titan Prometheus, joined the lanthanides in 1945 when Manhattan Project researchers Marinsky, Glendenin and Coryell identified the isotope promethium-147 among uranium fission byproducts. Confirming their breakthrough with mass spectrometry, they published the discovery in 1947. However, promethium's fleeting existence and intense radioactivity restrict applications to specialized research. With no stable isotopes, natural promethium persists only temporarily through spontaneous radioactive decay. Trace creation during uranium fission also generates vanishingly small amounts. Despite limited uses, the identification of this ephemeral element provided insights into the deep mysteries of atomic reactivity.

While promethium-145 endures longest, applications focus on the more readily produced promethium-147 isotope. As luminous paint, atomic batteries, and thickness gauges, promethium compounds deliver specialized capabilities despite the element's extreme rarity. Practical uses leverage promethium's radioactivity and fluorescence rather than its ephemeral metallic form. Even for this rarest of rare earths, narrow yet innovative applications persist.

Properties

Chemical Properties

Promethium's pervasive instability hinders scientific study and daily applications of this rare earth element. Still, research revealed key chemical properties including reactivity with halogens, variable oxidation states from +2 to +5, and luminescence of trivalent ions. While fleeting, promethium's radioactivity enables specialized uses.

The radioactive rare earth promethium exists only fleetingly through decay chains. All isotopes emit beta radiation, yet the synthetic promethium-147 enabled discovery and early characterization. Thermal neutron bombardment of enriched uranium produces promethium-147 initially. Then neodymium-146 absorbs neutrons, becoming neodymium-147 which beta decays over 11 days into promethium-147. Though other radioactive isotopes were synthesized, intrinsic instability has hindered extensive research. In aqueous solutions, promethium forms pink, water-soluble nitrate crystals when treated with nitric acid. Conversely, ammonia precipitates insoluble, light brown hydroxide sediment from Pm3+ ions. The sulfate exhibits slight solubility, while the oxide resembles samarium's more than neodymium's. Further, heating the oxide powder to 600°C induces cubic crystallization, later transitioning to monoclinic and hexagonal phases at 800°C and 1750°C through irreversible annealing.

Physical properties

Though ephemeral, metallic promethium's appearance resembles other silver-white rare earths. When forming luminescent salts, promethium's pale glow hints at its fleeting existence. Extremely high melting and boiling points, 1908°F and 5432°F respectively, reflect the element's radioactivity. With 61 electrons, promethium atoms readily lose the two outermost and a 4f electron during compound formation. Among the lanthanides, promethium's atomic radius ranks second largest, slightly exceeding its neighbors. Many attributes stem from promethium's position among the rare earths, including a double hexagonal close-packed structure. With hardness of 63 kg/mm2, the métal challenges study and applications. Still promethium's rarity captivates researchers probing the origins and impacts of this ephemeral element's radioactive properties.

Applications

 Radioluminescent Paints - Promethium-147's radioactivity causes certain phosphors to glow, allowing it to make self-luminous paints for signs, watches, and instrumentation.

 Nuclear Batteries - Promethium's radioactivity enables betavoltaic nuclear batteries with exceptionally long lifespans, used for pacemakers, space probes, and military applications.

 Thickness Gauges - Promethium-147's easily detectable radiation penetrates materials, making it useful for measuring paper, metal, and plastic thickness.

 Radiation Sources - Promethium serves as a portable, safer alternative to radium in applications such as producing X-rays and irradiating materials.

 Research - Scientists utilize promethium, the only radioactive rare earth metal, to study fundamental topics like nuclear processes, rare earth chemistry, and luminescence.

 Tracers - Due to their traceability, promethium isotopes are used as tracers for diagnostic imaging and biochemical research.

 Despite its scarcity, promethium's unique radioactivity enables specialized applications and research investigations into elemental origins and behavior.

Conclusion

The sole radioactive lanthanide, promethium-147 enables the few practical applications of element 61. Despite being the most stable isotope, promethium-145 is too scarce and ephemeral for use. Instead, the synthetic promethium-147 isotope, employed in luminous paints and thickness gauges, allows specialized utilization. Overall, promethium's pervasive instability restricts most research to investigating the fundamental chemical and radioactive properties of this rarest naturally occurring element. Trace amounts arise fleetingly through radioactive decay, but applications leverage promethium's radiance, not its elusive metallic form.