Applications

Interesting Facts

Discovery

A trio of American scientists at Oak Ridge National Laboratory (ORNL), Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell discovered promethium in 1945 (Weeks and Leicester, 1968, p. 835). The element was separated and analyzed from the fission products of uranium fuel irradiated in a graphite reactor. The discovery team did not announce their findings until 1947 because of critical research that was underway at ORNL during World War II. The name Prometheum was suggested by Mary Coryell, wife of one of the discoverers, after the mythological Greek Titan, Prometheus, who stole fire from the gods on Mount Olympus and brought it down to Earth (Marinsky, Glendenin, and Coryell, 1947). The International Union of Pure and Applied Chemistry accepted the discovery, however, they changed the spelling to Promethium to conform to the other elements (Weeks and Leicester, 1968, p. 835).

Definition

Promethium is a silver-white metal that tarnishes slowly in air to a pink tint and burns readily in air at 150 °C. No stable isotopes of the element exist and 38 radioisotopes have been identified. The original isotope discovered was Promethium-147 which has a half-life of 2.62 years, and is a uranium fission product from nuclear reactors via the beta decay of neodymium-147. Promethium-145 has the longest half-life at 17.7 years. The metal has a double hexagonal close-packed structure, a density of 7.22 g/cm3, a melting point of 1168 °C, and an estimated boiling point of 2460 °C (Wheelwright, 1969). Promethium oxide, or promethia, is a pale pink color and occurs as a sesquioxide with the formula Pm₂O₃. Dependant on temperature, the oxide occurs in three crystal systems. At ambient temperatures, promethium oxide occurs in cubic form with a specific gravity of 6.85 g/cm³, above 750-800 °C it occurs in monoclinic form with a specific gravity of 7.48 g/cm³, and above 1740 °C it occurs in hexagonal form with a specific gravity of 7.62 g/cm³ (Chikalla, McNeilly, and Roberts, 1972).

Preparation of Metal

The first promethium metal was prepared in 1963 by the reduction of PmF₃ with Li vapor (Weigel, 1963). Promethium-147 metal is prepared using calciothermic reduction of the trihalide, typically anhydrous PmCl₃. The reduction uses high-purity calcium metal as a reductant to reduce the PmCl₃ in a magnesium oxide crucible. Additional purification to remove the calcium and magnesium impurities requires a vacuum distillation step to yield a high-purity promethium metal (Wheelwright, 1969).

Source

Naturally Occurring: Trace amounts of promethium have been found in naturally occurring minerals. A sample of the mineral pitchblende has been found to contain promethium at a concentration of four parts per quintillion (10¹⁸) by mass (Attrep and Kuroda, 1968). Promethium occurs naturally in the Earth's crust at miniscule concentrations. By calculating the content of promethium at secular equilibrium in the Earth's crust, about 560 grams would naturally occur as a result of the spontaneous fission of uranium-238 and about 12 grams would naturally occur due to the alpha decay of europium-151 (Belli and others, 2007).

Manmade: All commercially used promethium is created in nuclear reactors. Traditional production of promethium-147 is from processing uranium fission products with high-activity and a yield of 2.25%. Although high-levels of radioactive waste are generated during the processing, this process is the primary method of production for commercial quantities. An alternate method of producing promethium-147 uses a High Flux Isotope Reactor (HFIR). In this process, enriched neodymium-146 is irradiated in the HFIR to create neodymium-147 in the peripheral target positions which decay to promethium-147. The yield from the HFIR process is lower than that from uranium fission but will provide promethium-147 in useful quantities of 500 to 1000 curies for research and development (Knapp, Mirzadeh, and Boll, 2007).

Mining

Promethium does not occur in sufficient quantities in the Earth's crust to be economically mined.

Selected promethium minerals

No promethium minerals have been discovered.

Selected minerals containing promethium

Uraninite, variety pitchblende¹ UO₂.

¹ Extremely small trace amounts of promethium have been identified in the uranium mineral pitchblende.

References

Attrep, Moses, Jr.; and P. K. Kuroda, 1968, Promethium in pitchblende: Journal of Inorganic and Nuclear Chemistry v. 30, no. 3, p. 699-703.

Beaudry and Bernard J. and Karl A. Gschneidner, Jr., 1978, Preparation and Basic Properties of the Rare Earth Metals: chapter 2 in Handbook of the Physics and Chemistry of Rare Earths-Volume 1:Metals, (Gschneidner, Jr. and Eyring, editors), North-Holland, New York, p. 173-232.

Belli, P., R. Bernabei, F. Cappella, R. Cerulli, C.J. Dai, F.A. Danevich, A. d'Angelo, A. Incicchitti, V.V. Kobychev, S.S. Nagorny, S. Nisi, F. Nozzoli, D. Prosperi, V.I. Tretyak, S.S. Yurchenko , 2007, Search for a decay of natural europium: Nuclear Physics, v. A, no. 789, p. 15-29.

Chikalla, T.D., C E. McNeilly, and E.P. Roberts, 1972, Polymorphic Modifications of Pm₂O₃: Journal of the American Ceramic Society, v. 55, no. 8, p. 428.

Knapp, F.F. (Russ), Saed Mirzadeh, and Rose Boll, 2007, ORNL Nuclear medicine program develops efficient method for separation of promethium-147 from reactor-produced neodymium-147: Isotope News, U.S. Department of Energy, Spring/Summer 2007, v. 1, issue 1, p. 5-7.

Marinsky, Jacob A., Lawrence E. Glendenin, and Charles D. Coryell, 1947, The chemical identification of radioisotopes of neodymium and element 61: Journal of the American Chemical Society, v. 69, p. 2781-2785.

Weeks, Mary E., and Henry M. Leicester, 1968, Discovery of the Elements (7th ed.): Easton, Pennsylvania, Journal of Chemical Education, 896 p.

Weigel, Fritz., 1963, Darstellung von metallischen promethium: Angewandte Chemie, May 21, v. 75, issue 10, p. 451.

Wheelwright, Earl J., 1969, Preparation of promethium-147 metal and determination of the density and melting points: Journal of Physical Chemistry, September, v. 78, no. 9, p. 2867-2871.