Fermium

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Animated Fermium

History

Fermium, element 100, is the eighth transuranium element of the actinide series and is named after the Italian physicist and Nobel Laureate Enrico Fermi. Element 100 was first discovered in 1952 in the fallout from the 10-megaton "Ivy Mike" nuclear test in the south Pacific the first successful test of a hydrogen fusion bomb. Researchers identified a new Pu-244 isotope found on filter papers on drone aircraft flown through the fallout. They determined that it could only have formed by the unexpected absorption of six neutrons by uranium-238 followed by successive beta-decays. At the time, the absorption of neutrons by a heavy nucleus was thought to be a rare process, but the identification of Pu-244 raised the possibility that still more neutrons could have been absorbed by the uranium nuclei leading to additional new elements.

Element 99, einsteinium was discovered almost immediately on other filter papers by Albert Ghiorso and co-workers at the Lawrence Berkeley Laboratory in collaboration with Argonne and Los Alamos National Laboratories, demonstrating that 15 neutrons were captured by U-238! The subsequent discovery of fermium required more material, as the yield of element 100 was expected to be at least an order of magnitude lower than that of einsteinium. So, contaminated coral from ground zero on Eniwetok atoll was shipped to Berkeley for processing and analysis. About two months after the Ivy-Mike test, a new activity was isolated emitting high-energy α-particles (7.1 MeV) with a half-life of about 1 day. It was the β− decay daughter of an isotope of einsteinium, and it had to be an isotope of element 100. : It was identified as 255Fm (half-life 20.07 hours). The discovery of the new elements, and the new data on neutron capture, was kept secret on the orders of the U.S. Military until 1955 due to Cold War tensions. Later the Berkeley team was able to prepare elements 99 and 100 in the lab by neutron bombardment of Pu-239 in a cyclotron. They published this work in 1954, with the disclaimer that these were not the first studies that had been carried out on the element. The 'Ivy Mike' studies were later declassified and published in 1955. Meanwhile, a group at the Nobel Institute for Physics in Stockholm independently claimed discovery of element 100 by producing an isotope with a 30-minute half-life and published their work in May 1954. Nevertheless, the historical precedence of the Berkeley team was generally recognized, and with it the prerogative to name the new element in honor of the recently deceased Enrico Fermi, the developer of the first artificial self-sustained nuclear reactor.

Uses

Owing to the minute amounts of fermium produced and all of its isotopes having relatively short half-lives, there are currently no uses for it outside of basic scientific research that expands knowledge of the rest of the periodic table.

Isotopes

A total of 21 known isotopes of fermium exist with atomic weights from 242 to 260, including 2 that are metastable. Fermium-257 is the longest-lived with a half-life of 100.5 days. Other relatively long-lived isotopes include Fm-253 (3 days), Fm-252 (25.4 hours) and Fm-255 (~20 hours). Fm-250, with a half-life of 30 minutes, was shown to be a decay product of nobelium, element 102 and the chemical identification of the isotope 250Fm confirmed the production and discovery of element 102. All the remaining isotopes of fermium have half-lives ranging from 30 minutes to less than a millisecond. The neutron-capture product of fermium-257, 258Fm, undergoes spontaneous fission with a half-life of just 370 microseconds; 259Fm and 260Fm are also unstable with respect to spontaneous fission (t½ = 1.5 s and 4 ms respectively). This means that the neutron capture production chain essentially terminates at mass number 257 because of the very short spontaneous fission half-lives of the heavier isotopes.

General Info

AtomicNumber
100
Symbol
Fm
Name
Fermium

Atomic Info

Appearance
AtomicWeight
[257]
Color
B31FBA
ElectronicConfiguration
[Rn] 5f12 7s2
ElectronegativityInPauling
1.3
AtomicRadiusInPM
IonRadiusInPM
VanDerWaalsRadiusInPM
IEinKJmol
627
EAinKJmol
OxidationStates
2, 3
StandardState
BondingType
MeltingPoint
1800
BoilingPoint
0
Density
0
State
Actinide
DiscoveredYear
1952