Curium

Curium. Synthetic element of the periodic table with symbol Cm and atomic number is 96. bombarding produces plutonium with alpha particles ( ions of helium ).

Summary

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  • 1 History
  • 2 Properties
  • 3 Preparation
  • 4 Abundance and natural state
  • 5 Uses
  • 6 Health effects
  • 7 Environmental effects
  • 8 External links
  • 9 Sources

History

Curium was produced synthetically in 1944 , by bombarding 239 Pu with alpha particles, by American chemists Glenn T. Seaborg , Ralph A. James, and Albert Ghiorso at the University of Berkeley, California .

The name Curio was chosen in honor of Marie Curie and her husband Pierre , famous for their discovery of radium and for other important work on radioactivity .

Werner and Perlman managed to isolate about 30 micrograms of the hydroxide of the isotope 242 Cm, in 1947 at the University of California .

Properties

It is a radioactive, silver-gray, artificially obtained metal, similar in properties to uranium , plutonium, and americium . It resembles gadolinium in some respects, although its crystal structure is more complex.

Chemical element, Cm, of the actinide series, with an atomic number of 96.

Curium does not exist in the Earth’s environment, but it can be produced artificially.

Its chemical properties are so close to those of typical rare earths that, were it not for its radioactivity, it could easily be mistaken for one of these elements. Known isotopes of curium include those with mass numbers 238 to 250, all of which are emitters of alpha particles.

The 244 Cm isotope is of particular interest because of its potential use as a compact source of thermoelectric force, using the heat generated by nuclear decay to generate electrical force.

Metallic curium can be produced by reduction of curium trifluoride with barium vapor. The metal has a silver luster, which is lost in contact with air, and a relative density of 13.5. The melting point is 1340 (+/-) 40 ° C (2444 +/- 72 ° F). Metal dissolves easily in common mineral acids, with formation of trippositive ion.

Several solid curium compounds have been prepared and their structures have been determined by X-ray diffraction. These include CmF 4 , CmF 3 , CmCl 3 , CmBr 3 , CmI 3 , Cm 2 O 3 , CmO 2 . In the lanthanides there are isostructural analogs of the curium compounds.

Property values:

Atomic Mass: [247] amu

Melting Point: 1613 K

Density: 13,510 kg / m 3

Normal Potential for Reduction: – 2.06 V Cm 3+ (Cm acid solution)

Heat of Fusion: 15.0 kJ / mol

Oxidation States: +3, +4

First Ionization Energy: 581 kJ / mol

Atomic Radius: 1.74 Å

Ionic Radius: Cm +3 = 0.98 Å Cm +4 = 0.88 Å

Atomic Volume: 18.28 cm ³ / mol

Polarizability: 23 ų

Electronegativity (Pauling): 1.3

Curium reacts with oxygen , water vapor, and acids and is more electropositive than aluminum . Most trivalent curium compounds are faintly yellow in color.

In 1950 , Crane, Wallmann and Cunningham found that the magnetic susceptibility of samples to CmF 3 was similar to that of GdF 3 which made it possible to assign the electron configuration to the ion Cm +3 . This same team, a year later, managed to prepare the curium in its elemental form for the first time.

So far fourteen isotopes of curium are known.

Preparation

The 242 Cm and 244 Cm isotopes can be obtained in quantities on the order of grams by bombarding 239 Pu with accelerated alpha particles, however the 248 Cm has only been produced in very small quantities, on the order of a few milligrams.

It can also be prepared from CmF 3 by reduction with barium .

Abundance and natural state

The half-life of the most stable isotope, about 16 million years, is very short compared to the age of the Earth, so the primitive curium, had it existed, would have long since disappeared.

Small amounts of curium probably exist in natural deposits of uranium minerals as a result of successive neutron captures and beta decays maintained by the low flux of natural neutrons present in these minerals. However, the presence of natural curium has never been detected.

Applications

Its main use is in obtaining other actinides. Curium isotopes, especially Cm-244, are poorly permeable to alpha radiation and are often used as shielding in satellites and unmanned space probes.

Curium-242 has been used to bombard the Moon’s soil with alpha particles because measuring the subsequent alpha emission from the soil provides information on the type and amount of many chemical elements present.

The energy power of 242 Cm is higher than that of 238 Pu so it can also be used as fuel.

Health effects

The curium absorbed by the body accumulates in the bone system and destroys the mechanism of cell wall formation, making it an element that poses serious health hazards.

Curium can enter the body through ingestion of food, water, or by breathing. Gastrointestinal absorption from food or water is the most likely source of any internal deposits of curium in the general population. After ingestion, most of the curium is excreted from the body within a few days and never enters the bloodstream; only about 0.05% of the amount ingested is absorbed into the bloodstream. Of the curium that reaches the blood, about 45% is deposited in the liver, where it is retained with a mean biological life of 20 years, and 45% is deposited in the bones where it is retained with a mean biological life of 50 years ( in simplified models that do not reflect immediate redistribution). Most of the remaining 10% is excreted directly.

Curium is generally a health hazard only if it enters the body; however, there is a small external risk associated with certain isotopes, for example curium 243, curium 245, and curium 247. The main forms of exposure are ingestion of food and water containing curium and inhalation of curium-contaminated dust. Ingestion is generally the exposure of greatest concern unless there is a nearby source of contaminated dust. Because curium enters the body much more easily if it is inhaled than if it is ingested, both routes of exposure can be important. The biggest health concern is bone tumors resulting from ionizing radiation emitted by curium isotopes deposited on the surface of bones.

In rats exposed to intravenous injection of curium 242 and curium 244, cancers of the skeleton, and cowbells of the lung and liver were observed in rats exposed by inhalation.

Environmental effects

Atmospheric testing of nuclear weapons, which ceased worldwide in 1980 , generated most of the environmental curium. Accidents and other leaks from nuclear weapons production facilities have led to localized contamination. Curium oxide is the most common form in the environment .

Curium is typically quite insoluble and adds strongly to soil particles. The concentration of curium in sandy soil particles is estimated to be about 4,000 times higher than in pore water (in the pore spaces between soil particles), and it binds even more strongly to loams where rates concentration are even higher (18,000).

 

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