promethium Chemische Eigenschaften,Einsatz,Produktion Methoden
Chemische Eigenschaften
Silvery-white metal. den-
sity 7.2.
Physikalische Eigenschaften
Promethium is a silvery-white, radioactive metal that is recovered as a by-product of uraniumfission. Promethium-147 is the only isotope generally available for study. The spectrallines of promethium can be observed in the light from a distant star in the constellationAndromeda. Even so, it is not found naturally on Earth, and scientists consider it to be anartificial element. Its melting point is 1,042°C, its boiling point is estimated at 3,000°C, andits density is 7.3 g/cm
3.
Isotopes
There are a total of 64 isotopes of promethium with half-lives ranging from twomilliseconds to over 17 years. There is no stable isotope, but Pm-147 with a half-lifeof 2.64 years is considered the most stable. No promethium is found naturally in theEarth’s crust. All of it is produced artificially from the leftover residue in nuclear reactors.
Origin of Name
Named for the Greek mythological god Prometheus, who stole fire
from Olympus and gave it to human beings.
Occurrence
Promethium is not found in nature. Therefore, it is by far the least abundant on Earth:none exists on the Earth. All of it is man-made in nuclear reactors. It is found only in thetransmuted decay by-products (“ashes”) from the fission of radioactive uranium.
Promethium (
61Pm) was predicted to fill a space between the rare-earths neodymium(
60Nd) and samarium (
62Sm) in the periodic table in 1902. Although a few scientists claimedto have produced it, separating promethium from other rare-earths proved to be difficult, andthus identifying it was elusive. Only small amounts are produced and exist.
Charakteristisch
Promethium was the missing element in the lanthanide rare-earth series in the periodictable. Since it does not exist on Earth, it was not recovered until nuclear reactors were common.Even so, scientists found it difficult to isolate it from other rare-earths.
When neodymiun-146 is bombarded with and captures neutrons, it becomes Nd-147 witha half-life of 11 days. Through beta decay, Nd-147 then becomes Pm-147 with a half-life of2.64 years. Other complicated neutron and beta decay reactions from these radioactive elementsare possible.
Verwenden
Promethium produces beta rays (high-energy electrons). These beta rays are used to producenuclear-powered batteries to provide electricity for spacecraft, as well as long-term usagefor up to five years in regions without electricity. It also could be used as a source of portableX-rays, as a gauge to measure the thickness of various materials, and to produce special lasersthat can communicate with submarines.
Promethium-147 is used in the manufacture of luminescent paint for watch dials, as wellas being a source of beta rays.
Definition
promethium: Symbol Pm. A soft silverymetallic element belonging tothe lanthanoids; a.n. 61; r.a.m. 145;r.d. 7.26 (20°C); m.p. 1080°C; b.p.2460°C. The only naturally occurringisotope, promethium–147, has a halflifeof only 2.52 years. Eighteen otherradioisotopes have been produced,but they have very short half-lives.The only known source of the elementis nuclear-waste material.Promethium–147 is of interest as abeta-decay power source but thepromethium–146 and –148, whichemit penetrating gamma radiation,must first be removed. It was discoveredby J. A. Marinsky, L. E. Glendenin,and C. D. Coryell in 1947.
Hazard
Promethium is an extremely strong radiation hazard. Because it is so rare, few peoplewill come in contact with it, but special precautions must be used when working with itsisotopes.
promethium Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
