Difference between revisions of "Fermium"

From WikiChem
Jump to: navigation, search
Line 26: Line 26:
 
'''Fermium''' (symbol: '''Fm''') is a synthetic [[chemical element]] and a member of the [[actinoid]] series. It is the heaviest element than can be formed by [[neutron]] bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities.
 
'''Fermium''' (symbol: '''Fm''') is a synthetic [[chemical element]] and a member of the [[actinoid]] series. It is the heaviest element than can be formed by [[neutron]] bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities.
  
 +
==Isotopes==
 +
There are 19 isotopes of fermium listed in N<small>UBASE</small>&nbsp;2003,<ref>{{NUBASE 2003}}.</ref> of which {{Nuclide|Z=100|A=257}} is the longest-lived with a [[half-life]] of 100.5&nbsp;days.
 
==Discovery==
 
==Discovery==
 
Fermium was first discovered in the fallout from the 'Ivy Mike' nuclear test (1&nbsp;November 1952), the first successful test of a hydrogen bomb. Initial examination of the debris from the explosion had shown the production of a new isotope of [[plutonium]], {{Nuclide|Z=94|A=244}}: this could only have formed by the absorption of six [[neutron]]s by a [[uranium-238]] nucleus followed by two [[Beta decay|β<sup>−</sup>&nbsp;decays]]. At the time, the absorption of neutrons by a heavy nucleus was thought to be a rare process, but the identification of {{Nuclide|Z=94|A=244}} raised the possibility that still more neutrons could have been absorbed by the uranium nuclei, leading to new elements.<ref name="Ghiorso">{{citation | first = Albert | last = Ghiorso | authorlink = Albert Ghiorso | year = 2003 | title = Einsteinium and Fermium | journal = Chem. Eng. News | url = http://pubs.acs.org/cen/80th/einsteiniumfermium.html | volume = 81 | issue = 36}}.</ref> Element&nbsp;99 ([[einsteinium]]) was quickly discovered on filter papers which had been flown through the cloud from the explosion (the same sampling technique that had been used to discover {{Nuclide|Z=94|A=244}}), specifically the isotope {{Nuclide|Z=99|A=254}} resulting from the capture of 16&nbsp;neutrons by uranium-238 followed by seven β<sup>−</sup>&nbsp;decays.<ref name="Ghiorso"/> The discovery of fermium (''Z''&nbsp;= 100) required more material, as the yield was expected to be at least an order of magnitude lower than that of element&nbsp;99, and so contaminated coral from the Enewetak atoll (where the test had taken place) was shipped to the [[University of California Radiation Laboratory]] in Berkeley, California, for processing and analysis. About two months after the test, a new component was isolated emitting high-energy [[α-particle]]s (7.1&nbsp;MeV) with a [[half-life]] of about a day. With such a short half-life, it could only arise from the β<sup>−</sup>&nbsp;decay of an isotope of einsteinium, and so had to be an isotope of the new element&nbsp;100: it was quickly identified as {{Nuclide|Z=100|A=255}} (''t''<sub>½</sub>&nbsp;= 20.07&nbsp;hours).<ref name="Ghiorso"/>
 
Fermium was first discovered in the fallout from the 'Ivy Mike' nuclear test (1&nbsp;November 1952), the first successful test of a hydrogen bomb. Initial examination of the debris from the explosion had shown the production of a new isotope of [[plutonium]], {{Nuclide|Z=94|A=244}}: this could only have formed by the absorption of six [[neutron]]s by a [[uranium-238]] nucleus followed by two [[Beta decay|β<sup>−</sup>&nbsp;decays]]. At the time, the absorption of neutrons by a heavy nucleus was thought to be a rare process, but the identification of {{Nuclide|Z=94|A=244}} raised the possibility that still more neutrons could have been absorbed by the uranium nuclei, leading to new elements.<ref name="Ghiorso">{{citation | first = Albert | last = Ghiorso | authorlink = Albert Ghiorso | year = 2003 | title = Einsteinium and Fermium | journal = Chem. Eng. News | url = http://pubs.acs.org/cen/80th/einsteiniumfermium.html | volume = 81 | issue = 36}}.</ref> Element&nbsp;99 ([[einsteinium]]) was quickly discovered on filter papers which had been flown through the cloud from the explosion (the same sampling technique that had been used to discover {{Nuclide|Z=94|A=244}}), specifically the isotope {{Nuclide|Z=99|A=254}} resulting from the capture of 16&nbsp;neutrons by uranium-238 followed by seven β<sup>−</sup>&nbsp;decays.<ref name="Ghiorso"/> The discovery of fermium (''Z''&nbsp;= 100) required more material, as the yield was expected to be at least an order of magnitude lower than that of element&nbsp;99, and so contaminated coral from the Enewetak atoll (where the test had taken place) was shipped to the [[University of California Radiation Laboratory]] in Berkeley, California, for processing and analysis. About two months after the test, a new component was isolated emitting high-energy [[α-particle]]s (7.1&nbsp;MeV) with a [[half-life]] of about a day. With such a short half-life, it could only arise from the β<sup>−</sup>&nbsp;decay of an isotope of einsteinium, and so had to be an isotope of the new element&nbsp;100: it was quickly identified as {{Nuclide|Z=100|A=255}} (''t''<sub>½</sub>&nbsp;= 20.07&nbsp;hours).<ref name="Ghiorso"/>

Revision as of 14:31, 23 September 2010

einsteinium ← fermium → mendelevium
Er
↑
Fm
↓
–
Atomic properties
Atomic number 100
Electron configuration [Rn] 5f12 6s2
Physical properties[1][Note 1]
Melting point 1125 K (850 °C)
Chemical properties[Note 1]
Electronegativity 1.3 (Pauling)
Ionization energy
6.50 eV
627 kJ mol−1
Atomic radii[1][2][3][Note 1]
Metallic radius 196 pm
Ionic radius 92 pm (Fm3+)
Thermodynamic properties[1]
Enthalpy change of atomization 142(13) kJ mol−1
Entropy change of atomization 98(13) J K−1 mol−1
Miscellaneous
CAS number 7440-72-4
Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).
This box: view • talk

Fermium (symbol: Fm) is a synthetic chemical element and a member of the actinoid series. It is the heaviest element than can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities.

Isotopes

There are 19 isotopes of fermium listed in NUBASE 2003,[4] of which 257100Fm is the longest-lived with a half-life of 100.5 days.

Discovery

Fermium was first discovered in the fallout from the 'Ivy Mike' nuclear test (1 November 1952), the first successful test of a hydrogen bomb. Initial examination of the debris from the explosion had shown the production of a new isotope of plutonium, 24494Pu: this could only have formed by the absorption of six neutrons by a uranium-238 nucleus followed by two β− decays. At the time, the absorption of neutrons by a heavy nucleus was thought to be a rare process, but the identification of 24494Pu raised the possibility that still more neutrons could have been absorbed by the uranium nuclei, leading to new elements.[5] Element 99 (einsteinium) was quickly discovered on filter papers which had been flown through the cloud from the explosion (the same sampling technique that had been used to discover 24494Pu), specifically the isotope 25499Es resulting from the capture of 16 neutrons by uranium-238 followed by seven β− decays.[5] The discovery of fermium (Z = 100) required more material, as the yield was expected to be at least an order of magnitude lower than that of element 99, and so contaminated coral from the Enewetak atoll (where the test had taken place) was shipped to the University of California Radiation Laboratory in Berkeley, California, for processing and analysis. About two months after the test, a new component was isolated emitting high-energy α-particles (7.1 MeV) with a half-life of about a day. With such a short half-life, it could only arise from the β− decay of an isotope of einsteinium, and so had to be an isotope of the new element 100: it was quickly identified as 255100Fm (t½ = 20.07 hours).[5]

The discovery of the new elements, and the new data on neutron capture, was initially kept secret on the orders of the U.S. military.[5] Nevertheless, the Berkeley team were able to prepare elements 99 and 100 by civilian means, through the neutron bombardment of plutonium-239, and published this work in 1954 with the disclaimer that it was not the first studies that had been carried out on the elements.[6][7] The 'Ivy Mike' studies were declassified and published in 1955.[8]

The Berkeley team had been worried that another group might discover lighter isotopes of element 100 through ion bombardment techniques before they could publish their classified research,[5] and this proved to be the case. A group at the Nobel Institute for Physics in Stockholm independently discovered the element, producing an isotope later confirmed to be 250100Fm by bombarding a 23892U target with oxygen-16 ions, and published their work in May 1954.[9] Nevertheless, the priority of the Berkeley team was generally recognized, and with it the prerogative to name the new element in honour of the recently deceased Enrico Fermi, the developer of the first artificial self-sustained nuclear reactor.

Production

Fermium is produced by the bombardment of lighter actinoids with neutrons in a nuclear reactor. The major source is the 85 MW High Flux Isotope Reactor at the Oak Ridge National Laboratory in Tennessee, USA, which is dedicated to the production of transcurium (Z > 96) elements.[10] In a "typical processing campaign" at Oak Ridge, tens of grams of curium are irradiated to produce decigram quantities of californium, milligram quantities of berkelium and einsteinium and picogram quantities of fermium.[11] However nanogram[12] and microgram[13] quantities of fermium can be prepared for specific experiments.

After production, the fermium must be separated from other actinoids and from lanthanoid fission products. This is usually achieved by ion exchange chromatography, with the standard process using a cation exchanger such as Dowex 50 or TEVA eluted with a solution of ammonium α-hydroxyisobutyrate.[14][15] Smaller cations form more stable complexes with the α-hydroxyisobutyrate anion, and so are preferentially eluted from the column.[16] A rapid fractional crystallization method has also been described.[17]

Notes and references

Notes

  1. ↑ 1.0 1.1 1.2 Many of the properties of fermium are only known through estimation and/or extrapolation. The melting point and metallic radius were estimated on the basis of the enthalpy change of atomization and comparison with divalent lanthanoids; the electronegativity was estimated on the basis of periodic trends; the ionic radius was estimated from the behaviour of Fm3+ α-hydroxyisobutyrate (α-HIB) complexes on ion exchange columns, and agrees well with theoretical calculations. The electron configuration and thermodynamic properties were directly determined.

References

  1. ↑ 1.0 1.1 1.2 Haire, Richard G.; Gibson, John K. The enthalpy of sublimation and thermodynamic functions of fermium. J. Chem. Phys. 1989, 91 (11), 7085–96. DOI: 10.1063/1.457326.
  2. ↑ David, F.; Samhoun, K.; Guillaumont, R.; Edelstein, N. Thermodynamic properties of 5f elements. J. Inorg. Nucl. Chem. 1978, 40 (1), 69–74. DOI: 10.1016/0022-1902(78)80309-1.
  3. ↑ Brüchle, W.; Schädel, M.; Scherer, U. W.; Kratz, J. V.; Gregorich, K. E.; Lee, D.; Nurmia, M.; Chasteler, R. M., et al. The hydration enthalpies of Md3+ and Lr3+. Inorg. Chim. Acta 1988, 146 (2), 267–76. DOI: 10.1016/S0020-1693(00)80619-2.
  4. ↑ Audi, G.; Bersillon, O.; Blachot, J.; Wapstra, A. H. The NUBASE evaluation of nuclear and decay properties. Nucl. Phys. A 2003, 729, 3–128. doi:10.1016/j.nuclphysa.2003.11.001, <http://amdc.in2p3.fr/nubase/Nubase2003.pdf>.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Ghiorso, Albert Einsteinium and Fermium. Chem. Eng. News 2003, 81 (36), <http://pubs.acs.org/cen/80th/einsteiniumfermium.html>.
  6. ↑ Thompson, S. G.; Ghiorso, A.; Harvey, B. G.; Choppin, G. R. Transcurium Isotopes Produced in the Neutron Irradiation of Plutonium. Phys. Rev. 1954, 93 (4), 908. DOI: 10.1103/PhysRev.93.908.
  7. ↑ Choppin, G. R.; Thompson, S. G.; Ghiorso, A.; Harvey, B. G. Nuclear Properties of Some Isotopes of Californium, Elements 99 and 100. Phys. Rev. 1954, 94 (4), 1080–81. DOI: 10.1103/PhysRev.94.1080.
  8. ↑ Ghiorso, A.; Thompson, S. G.; Higgins, G. H.; Seaborg, G. T.; Studier, M. H.; Fields, P. R.; Fried, S. M.; Diamond, H., et al. New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100. Phys. Rev. 1955, 99 (3), 1048–49. DOI: 10.1103/PhysRev.99.1048.
  9. ↑ Atterling, Hugo; Forsling, Wilhelm; Holm, Lennart W.; Melander, Lars; Åström, Björn Element 100 Produced by Means of Cyclotron-Accelerated Oxygen Ions. Phys. Rev. 1954, 95 (2), 585–86. DOI: 10.1103/PhysRev.95.585.2.
  10. ↑ High Flux Isotope Reactor; Oak Ridge National Laboratory, <http://neutrons.ornl.gov/facilities/HFIR/>. (accessed 23 September 2010).
  11. ↑ Porter, C. E.; Riley, F. D., Jr.; Vandergrift, R. D.; Felker, L. K. Fermium Purification Using Teva™ Resin Extraction Chromatography. Sep. Sci. Technol. 1997, 32 (1–4), 83–92. DOI: 10.1080/01496399708003188.
  12. ↑ Sewtz, M.; Backe, H.; Dretzke, A.; Kube, G.; Lauth, W.; Schwamb, P.; Eberhardt, K.; Grüning, C., et al. First Observation of Atomic Levels for the Element Fermium (Z = 100). Phys. Rev. Lett. 2003, 90 (16), 163002. DOI: 10.1103/PhysRevLett.90.163002.
  13. ↑ Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; p 1463. ISBN 0-08-022057-6.
  14. ↑ Choppin et al. (1956)
  15. ↑ Silva, Robert J. Fermium, Mendelevium, Nobelium, and Lawrencium. In The Chemistry of the Actinide and Transactinide Elements, 3rd ed.; Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, Eds.; Springer: Dordrecht, 2006; Vol. 3, Chapter 13, pp 1621–51. doi:10.1007/1-4020-3598-5_13, <http://radchem.nevada.edu/classes/rdch710/files/Fm%20to%20Lr.pdf>.
  16. ↑ Katz et al. (1986)
  17. ↑ Vobecky´ et al. (1991)

Further reading

External links

Wikipedia-logo.png See also the corresponding article on Wikipedia.
Error creating thumbnail: Unable to save thumbnail to destination
 This page is currently licensed under the Creative Commons Attribution 3.0 Unported license and any later versions of that license.
Retrieved from "https://wiki.potsdam.edu/wikichem/index.php?title=Fermium&oldid=10893"