Fermium
Fermium
History
(Enrico Fermi) Fermium, the eighth discovered transuranium element of the actinide series, was identified by Ghiorso and co-workers in 1952 in the debris from a thermonuclear explosion in the pacific during work involving the University of California Radiation Laboratory, Argonne National Laboratory, and Los Alamos Scientific Laboratory.
The isotope produced was the 20-hour 255Fm. During 1953 and early 1954, while discovery of elements 99 and 100 was withheld from publication for security reasons, a group from the Nobel Institute of Physics in Stockholm bombarded 238U with 16O ions, and isolated a 30-min alpha-emitter, which they ascribed to 250-100, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed.
Properties
The chemical properties of fermium have been studied solely with tracer amounts. In normal aqueous media, only the (III) oxidation state appears to exist.
Isotopes
254Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements, such as plutonium, using a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached.
Sixteen isotopes of fermium are known to exist. 257Fm, with a half-life of about 100.5 days, is the longest lived. 250Fm, with a half-life of 30 minutes, has been shown to be a decay product of element 254-102. Chemical identification of 250Fm confirmed the production of element 102 (nobelium).
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
http://pearl1.lanl.gov/periodic/elements/100.html (1 of 2) [3/6/2001 8:38:25 AM]
Fermium
Last Updated: 12/19/97, CST Information Services Team
http://pearl1.lanl.gov/periodic/elements/100.html (2 of 2) [3/6/2001 8:38:25 AM]
Mendelevium
Mendelevium
History
(Dmitri Mendeleev) Mendelevium, the ninth transuranium element of the actinide series discovered, was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg in early in 1955 during the bombardment of the isotope 253Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was 256Md, which has a half-life of 76 min. This first identification was notable in that 256Md was synthesized on a one-atom-at-a-time basis.
Isotopes
Fourteen isotopes are now recognized. 258Md has a half-life of 2 months. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. Eventually enough 258Md should be made to determine its physical properties.
Uses
256Md has been used to elucidate some of the chemical properties of mendelevium in aqueous solution.
Properties
Experiments seem to show that the element possesses a moderately stable dipositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of the actinide elements.
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team
http://pearl1.lanl.gov/periodic/elements/101.html [3/6/2001 8:38:25 AM]
Lawrencium
Lawrencium
History
(Ernest O. Lawrence, inventor of the cyclotron) This member of the 5f transition elements (actinide series) was discovered in March 1961 by A. Ghiorso, T. Sikkeland, A.E. Larsh, and R.M. Latimer. A 3-Mg californium target, consisting of a mixture of isotopes of mass number 249, 250, 251, and 252, was bombarded with either 10B or 11B. The electrically charged transmutation nuclei recoiled with an atmosphere of helium and were collected on a thin copper conveyor tape which was then moved to place collected atoms in front of a series of solid-state detectors. The isotope of element 103 produced in this way decayed by emitting an 8.6 MeV alpha particle with a half-life of 8 s.
In 1967, Flerov and associates at the Dubna Laboratory reported their inability to detect an alpha emitter with a half-life of 8 s which was assigned by the Berkeley group to 257-103. This assignment has been changed to 258Lr or 259Lr.
In 1965, the Dubna workers found a longer-lived lawrencium isotope, 256Lr, with a half-life of 35 s. In 1968, Thiorso and associates at Berkeley used a few atoms of this isotope to study the oxidation behavior of lawrencium. Using solvent extraction techniques and working very rapidly, they extracted lawrencium ions from a buffered aqueous solution into an organic solvent -- completing each extraction in about 30 s.
Properties
Lawrencium behaves differently from dipositive nobelium and more like the tripositive elements earlier in the actinide series.
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97 CST Information Services Team
http://pearl1.lanl.gov/periodic/elements/103.html [3/6/2001 8:38:25 AM]