прометий

silvery metal; enthalpy of sublimation is 348kJ/mol (estimated); radius of atom is 0.1811nm; radius of ion is 0.0979 nm; Pr+++has yellow-colored solutions [KIR82]

Silvery-white metal; density 7.22 g/cm³; because of radioactivity, the metal and its salts luminesce in the dark giving a pale blue or greenish glow; melts at 168+6°C; vaporizes at 2,460°C; insoluble in water.

The discovery of this element is credited to J.A. Marinsky and L.E. Glendenin who, in 1945, identified its long-lived isotope Pm-147 (t_1/2 2.64 years) in the fission products of uranium. They named the element after Prometheus, who according to Greek mythology stole fire from heaven. The element was first isolated from fission product wastes by G.W. Parker and P.M. Lantz in 1948. It first was recovered from natural sources by O. Erametsa in 1965. An amount less than 0.5 g was recovered from 20 tons of rare earths.
Promethium does not occur in metallic form in nature. Minute quantities are associated with other rare earths. It also is detected in uranium fission products. It is probably the rarest of the lanthanide elements.
Promethium has very limited applications. It is used in phosphor lights to produce signals. Also, it is used as a beta particle source for thickness gages, nuclear batteries, and portable x-ray units.

Promethium-147 is used in the manufacture of luminescent paint for watch dials, as well as being a source of beta rays.

Promethium-147, the isotope used commercially, is isolated from fission product wastes. The radioactive materials must be handled safely in a glove box. The metal complexes either with ethlenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) and is isolated by elution from Dowex 50.
The metal may be obtained from its fluoride salt, promethium(III) fluoride by heating with lithium metal in a double tantalum crucible at 700 to 800°C in vacuum and then increasing the temperature to 1,100°C.