Promethium

MELTING POINT: 1,100°C
BOILING POINT: 3,000°C
DENSITY: 7.22 g/cm³
MOST COMMON IONS: Pm³⁺

The existence of promethium was first theorized in 1902 by Bohuslav Brauner, who predicted that an element between neodymium and samarium was missing from the periodic table. Because only minuscule amounts of promethium are naturally present in Earth's crust, full confirmation of this prediction was not made until 1945. Working at the Oak Ridge National Laboratory in Oak Ridge, Tennessee, Jacob Marinsky, Lawrence Glendenin, and Charles Coryell produced promethium by the nuclear fission of uranium and by neutron irradiation of neodymium, chemically identifying the new element using ion exchange chromatography.

In compounds, promethium is known to exist in the tripositive oxidation state only (Pm³⁺), which is the most stable oxidation state for all of the rare earth elements. Consequently, its chemistry is like that of other rare earth elements and of the tripositive actinide ions, especially Am³⁺ , which is almost the same size as Pm³⁺. When enough material is present to see, promethium compounds are generally a pale pink color under white light. In the dark, however, the intense radioactivity of all promethium isotopes causes macroscopic amounts of promethium compounds to glow pale blue or green. The isotope ¹⁴⁵Pm has the longest half-life (17.7 years), but ¹⁴⁷Pm (half-life 2.6234 years) is produced in significant quantities from the fission of uranium and plutonium in nuclear reactors, and convenient methods for isolating gram amounts of ¹⁴⁷Pm by displacement chromatography have been described. The availability, high specific activity (928 Ci/gram), and pure β-particle emission of ¹⁴⁷Pm lend it to industrial applications in thickness gauges, nuclear batteries, and emergency lights that operate without an external power source.

Promethium

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