Editing Fermium (section)

==Discovery==
[[File:Ivy Mike - mushroom cloud.jpg|thumb|left|Fermium was first observed in the fallout from the ''Ivy Mike'' nuclear test.]]
[[File:Enrico Fermi 1943-49.jpg|thumb|left|The element was named after [[Enrico Fermi]].]]
[[File:Albert Ghiorso ca 1970.jpg|thumb|right|The element was discovered by a team headed by [[Albert 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.<ref name="lanl">{{cite web| url=http://periodic.lanl.gov/elements/99.html|title=Einsteinium|access-date=2007-12-07|archive-url=https://web.archive.org/web/20071026052909/http://periodic.lanl.gov/elements/99.html <!--Added by H3llBot-->|archive-date=2007-10-26}}</ref><ref name="nrc">[http://www.nrc-cnrc.gc.ca/eng/education/elements/el/fm.html Fermium – National Research Council Canada] {{webarchive|url=https://web.archive.org/web/20101225025414/http://www.nrc-cnrc.gc.ca/eng/education/elements/el/fm.html |date=2010-12-25 }}. Retrieved 2 December 2007</ref><ref name="Ghiorso" /> Initial examination of the debris from the explosion had shown the production of a new isotope of [[plutonium]], [[plutonium-244|{{nuclide|Pu|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|Pu|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">{{cite journal|first = Albert|last = Ghiorso|author-link = Albert Ghiorso|date = 2003 |title = Einsteinium and Fermium|journal = Chemical and Engineering News|url = http://pubs.acs.org/cen/80th/einsteiniumfermium.html|volume = 81|issue = 36|doi = 10.1021/cen-v081n036.p174|pages = 174–175|url-access = subscription}}</ref>

Element&nbsp;99 ([[einsteinium]]) was quickly discovered on filter papers which had been flown through clouds from the explosion (the same sampling technique that had been used to discover {{nuclide|Pu|Z=94|A=244}}).<ref name="Ghiorso" /> It was then identified in December 1952 by [[Albert Ghiorso]] and co-workers at the [[University of California at Berkeley]].<ref name="lanl" /><ref name="nrc" /><ref name="Ghiorso" /> They discovered the isotope <sup>253</sup>Es ([[half-life]] {{val|20.5|u=days}}) that was made by the [[neutron capture|capture]] of 15 [[neutron]]s by [[uranium-238]] nuclei – which then underwent seven successive [[beta decay]]s:
<blockquote>
{{NumBlk|:|<math chem>\ce{^{238}_{92}U ->[\begin{matrix} \\ +15\ce{n}\end{matrix}][\begin{matrix} 7\beta^- \\ \end{matrix}] {}^{253}_{99}Es}</math>|{{EquationRef|1}}}}
</blockquote>
Some <sup>238</sup>U atoms, however, could capture another amount of neutrons (most likely, 16 or 17).

The discovery of fermium ({{nowrap|''Z'' {{=}} 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 ({{val|7.1|ul=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 <sup>255</sup>Fm ({{nowrap|''t'' {{=}} {{val|20.07|(7)|ul=hours}}}}).<ref name="Ghiorso" />

The discovery of the new elements, and the new data on neutron capture, was initially kept secret on the orders of the U.S.&nbsp;military until 1955 due to [[Cold War]] tensions.<ref name="Ghiorso" /><ref name = "PhysRev.99.1048" >{{cite journal
| last1 = Ghiorso
| first1 = A.
| last2 = Thompson
| first2 = S.
| last3 = Higgins
| first3 = G.
| last4 = Seaborg
| first4 = Glenn T.
| last5 = Studier
| first5 = M.
| last6 = Fields
| first6 = P.
| last7 = Fried
| first7 = S.
| last8 = Diamond
| first8 = H.
| last9 = Mech
| first9 = J.
| last10 = Pyle
| first10 = G.
| last11 = Huizenga
| first11 = J.
| last12 = Hirsch
| first12 = A.
| last13 = Manning
| first13 = W.
| last14 = Browne
| first14 = C.
| last15 = Smith
| first15 = H.
| last16 = Spence
| first16 = R.
| title = New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100
| journal = Phys. Rev.
| volume = 99
| issue = 3
| doi = 10.1103/PhysRev.99.1048
| pages = 1048–1049
| date = 1955|bibcode = 1955PhRv...99.1048G | display-authors = 8
| url = https://cloudfront.escholarship.org/dist/prd/content/qt70q401ct/qt70q401ct.pdf
| doi-access = free
}}</ref><ref>Fields, P. R.; Studier, M. H.; Diamond, H.; Mech, J. F.; Inghram, M. G. Pyle, G. L.; Stevens, C. M.; Fried, S.; Manning, W. M. (Argonne National Laboratory, Lemont, Illinois); Ghiorso, A.; Thompson, S. G.; Higgins, G. H.; Seaborg, G. T. (University of California, Berkeley, California): "Transplutonium Elements in Thermonuclear Test Debris", in: {{cite journal|last1=Fields|first1=P.|last2=Studier|first2=M.|last3=Diamond|first3=H.|last4=Mech|first4=J.|last5=Inghram|first5=M.|last6=Pyle|first6=G.|last7=Stevens|first7=C.|last8=Fried|first8=S.|last9=Manning|first9=W. |last10=Ghiorso|first10=A.|last11=Thompson|first11=S.|last12=Higgins|first12=G.|last13=Seaborg|first13=G.|title=Transplutonium Elements in Thermonuclear Test Debris|journal=Physical Review|volume=102|issue=1|pages=180|date=1956|doi=10.1103/PhysRev.102.180|bibcode = 1956PhRv..102..180F }}</ref> Nevertheless, the Berkeley team was 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.<ref name = "PhysRev.93.908">{{cite journal|first1 = S. G.|last1 = Thompson |first2 = A.|last2 = Ghiorso|author-link2 = Albert Ghiorso|first3 = B. G.|last3 = Harvey|first4 = G. R.|last4 = Choppin|title = Transcurium Isotopes Produced in the Neutron Irradiation of Plutonium|journal = Physical Review|volume = 93|issue = 4|page = 908|date = 1954|doi = 10.1103/PhysRev.93.908|bibcode = 1954PhRv...93..908T |url = https://escholarship.org/content/qt2wj6c5kh/qt2wj6c5kh.pdf?t=p0wtgb |doi-access = free}}</ref><ref>{{cite journal|first1 = G. R.|last1 = Choppin|first2 = S. G.|last2 = Thompson|first3 = A.|last3 = Ghiorso|author-link3 = Albert Ghiorso|first4 = B. G.|last4 = Harvey|title = Nuclear Properties of Some Isotopes of Californium, Elements 99 and 100|journal = Physical Review|volume = 94|issue = 4|pages = 1080–1081|date = 1954|doi = 10.1103/PhysRev.94.1080|bibcode = 1954PhRv...94.1080C |doi-access = free}}</ref> The "Ivy Mike" studies were declassified and published in 1955.<ref name = "PhysRev.99.1048" />

The Berkeley team had been worried that another group might discover lighter isotopes of element&nbsp;100 through ion-bombardment techniques before they could publish their classified research,<ref name="Ghiorso" /> 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 <sup>250</sup>Fm ({{nowrap|''t''<sub>1/2</sub> {{=}} {{val|30|ul=minutes}}}}) by bombarding a {{nuclide|U|Z=92|A=238}} target with [[oxygen-16]] ions, and published their work in May 1954.<ref>{{cite journal|last1 = Atterling|first1 = Hugo|last2 = Forsling|first2 = Wilhelm|last3 = Holm |first3 = Lennart W.|last4 = Melander|first4 = Lars|last5 = Åström|first5 = Björn|date = 1954|title = Element 100 Produced by Means of Cyclotron-Accelerated Oxygen Ions|journal = Physical Review|volume = 95|issue = 2|pages = 585–586|doi = 10.1103/PhysRev.95.585.2|bibcode = 1954PhRv...95..585A }}</ref> Nevertheless, the priority of the Berkeley team was generally recognized, and with it the prerogative to name the new element in honour of [[Enrico Fermi]], the developer of the first artificial self-sustained nuclear reactor. Fermi was still alive when the name was proposed, but had died by the time it became official.<ref>{{cite book |last1=Hoffman |first1=D. C. |author-link=Darleane C. Hoffman |last2=Ghiorso |first2=A. |author-link2=Albert Ghiorso |last3=Seaborg |first3=G. T. |title=The Transuranium People: The Inside Story |year=2000 |publisher=[[World Scientific]] |isbn=978-1-78-326244-1 |pages=187–189}}</ref>