Editing Mendelevium (section)

==Discovery==
[[File:Berkeley 60-inch cyclotron.jpg|thumb|upright=0.7|left|The 60-inch cyclotron at the Lawrence Radiation Laboratory, [[University of California, Berkeley]], in August 1939|alt=Black-and-white picture of heavy machinery with two operators sitting aside]]
Mendelevium was the ninth [[transuranic element]] to be synthesized. It was first [[discovery of the chemical elements|synthesized]] by [[Albert Ghiorso]], [[Glenn T. Seaborg]], [[Gregory Robert Choppin]], Bernard G. Harvey, and team leader [[Stanley G. Thompson]] in early 1955 at the University of California, Berkeley. The team produced <sup>256</sup>Md ([[half-life]] of 77.7 minutes{{NUBASE2020|ref}}) when they bombarded an <sup>253</sup>[[einsteinium|Es]] target consisting of only a [[1,000,000,000|billion]] (10<sup>9</sup>) einsteinium atoms with [[alpha particle]]s ([[helium]] nuclei) in the [[Berkeley Radiation Laboratory]]'s 60-inch [[cyclotron]], thus increasing the target's atomic number by two. <sup>256</sup>Md thus became the first isotope of any element to be synthesized one atom at a time. In total, seventeen mendelevium atoms were produced.<ref name="discovery">{{cite book|doi=10.1103/PhysRev.98.1518|url=https://books.google.com/books?id=e53sNAOXrdMC&pg=PA101|title=New Element Mendelevium, Atomic Number 101|date=1955|last1=Ghiorso|first1=A.|last2=Harvey|first2=B.|last3=Choppin|first3=G.|last4=Thompson|first4=S.|last5=Seaborg|first5=Glenn T.|journal=Physical Review|volume=98|pages=1518–1519|bibcode = 1955PhRv...98.1518G|isbn=9789810214401|issue=5 }}</ref> This discovery was part of a program, begun in 1952, that irradiated [[plutonium]] with neutrons to transmute it into heavier actinides.<ref name="Choppin">{{cite journal|first = Gregory R.|last = Choppin|date = 2003 |title = Mendelevium|journal = Chemical and Engineering News|url = http://pubs.acs.org/cen/80th/mendelevium.html|volume = 81|issue = 36}}</ref> This method was necessary as the previous method used to synthesize transuranic elements, [[neutron capture]], could not work because of a lack of known [[beta decay]]ing [[isotopes of fermium]] that would produce isotopes of the next element, mendelevium, and also due to the very short half-life to [[spontaneous fission]] of <sup>258</sup>[[fermium|Fm]] that thus constituted a hard limit to the success of the neutron capture process.{{NUBASE2020|ref}}

{{External media
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| video1= [https://www.youtube.com/watch?v=DrssJRb301k Reenactment of the discovery of mendelevium] at Berkeley 
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To predict if the production of mendelevium would be possible, the team made use of a rough calculation. The number of atoms that would be produced would be approximately equal to the product of the number of atoms of target material, the target's cross section, the ion beam intensity, and the time of bombardment; this last factor was related to the half-life of the product when bombarding for a time on the order of its half-life. This gave one atom per experiment. Thus under optimum conditions, the preparation of only one atom of element 101 per experiment could be expected. This calculation demonstrated that it was feasible to go ahead with the experiment.<ref name="discovery" /> The target material, einsteinium-253, could be produced readily from irradiating [[plutonium]]: one year of irradiation would give a billion atoms, and its three-week [[half-life]] meant that the element 101 experiments could be conducted in one week after the produced einsteinium was separated and purified to make the target. However, it was necessary to upgrade the cyclotron to obtain the needed intensity of 10<sup>14</sup> alpha particles per second; Seaborg applied for the necessary funds.<ref name="Choppin" />

[[File:Md datasheet.jpg|thumb|left|The data sheet, showing stylus tracing and notes, that proved the discovery of mendelevium.]]
While Seaborg applied for funding, Harvey worked on the einsteinium target, while Thomson and Choppin focused on methods for chemical isolation. Choppin suggested using [[α-hydroxyisobutyric acid]] to separate the mendelevium atoms from those of the lighter actinides.<ref name="Choppin" /> The actual synthesis was done by a recoil technique, introduced by Albert Ghiorso. In this technique, the einsteinium was placed on the opposite side of the target from the beam, so that the recoiling mendelevium atoms would get enough [[momentum]] to leave the target and be caught on a catcher foil made of gold. This recoil target was made by an electroplating technique, developed by Alfred Chetham-Strode. This technique gave a very high yield, which was absolutely necessary when working with such a rare and valuable product as the einsteinium target material.<ref name="discovery" /> The recoil target consisted of 10<sup>9</sup> atoms of <sup>253</sup>Es which were deposited electrolytically on a thin gold foil. It was bombarded by 41&nbsp;[[MeV]] [[alpha particle]]s in the [[Berkeley cyclotron]] with a very high beam density of 6×10<sup>13</sup> particles per second over an area of 0.05&nbsp;cm<sup>2</sup>. The target was cooled by water or [[liquid helium]], and the foil could be replaced.<ref name="discovery" /><ref name="book1">{{cite book|url=https://books.google.com/books?id=4KcVj3xqsrAC&pg=PA40|pages=40–42|title=On beyond uranium: journey to the end of the periodic table|author=Hofmann, Sigurd|publisher=CRC Press|isbn=978-0-415-28496-7|date=2002}}</ref>

Initial experiments were carried out in September 1954. No alpha decay was seen from mendelevium atoms; thus, Ghiorso suggested that the mendelevium had all decayed by [[electron capture]] to [[fermium]] and that the experiment should be repeated to search instead for [[spontaneous fission]] events.<ref name="Choppin" /> The repetition of the experiment happened in February 1955.<ref name="Choppin" />

[[File:DIMendeleevCab.jpg|thumb|right|The element was named after [[Dmitri Mendeleev]].]]
On the day of discovery, 19 February, alpha irradiation of the einsteinium target occurred in three three-hour sessions. The cyclotron was in the [[University of California]] campus, while the Radiation Laboratory was on the next hill. To deal with this situation, a complex procedure was used: Ghiorso took the catcher foils (there were three targets and three foils) from the cyclotron to Harvey, who would use [[aqua regia]] to dissolve it and pass it through an [[anion]]-exchange [[resin]] column to separate out the [[transuranium element]]s from the gold and other products.<ref name="Choppin" /><ref name="book2">{{cite book|url=https://archive.org/details/newchemistry00hall|url-access=registration|pages=[https://archive.org/details/newchemistry00hall/page/9 9]–11|title=The new chemistry|author=Hall, Nina|publisher=Cambridge University Press|date=2000|isbn=978-0-521-45224-3}}</ref> The resultant drops entered a [[test tube]], which Choppin and Ghiorso took in a car to get to the Radiation Laboratory as soon as possible. There Thompson and Choppin used a [[cation]]-exchange resin column and the α-hydroxyisobutyric acid. The solution drops were collected on [[platinum]] disks and dried under heat lamps. The three disks were expected to contain respectively the fermium, no new elements, and the mendelevium. Finally, they were placed in their own counters, which were connected to recorders such that spontaneous fission events would be recorded as huge deflections in a graph showing the number and time of the decays. There thus was no direct detection, but by observation of spontaneous fission events arising from its electron-capture daughter <sup>256</sup>Fm. The first one was identified with a "hooray" followed by a "double hooray" and a "triple hooray". The fourth one eventually officially proved the chemical identification of the 101st element, mendelevium. In total, five decays were reported up until 4&nbsp;a.m. Seaborg was notified and the team left to sleep.<ref name="Choppin" /> Additional analysis and further experimentation showed the produced mendelevium isotope to have mass 256 and to decay by electron capture to fermium-256 with a half-life of 157.6&nbsp;minutes.{{NUBASE2020|ref}}

{{quotation|We thought it fitting that there be an element named for the Russian chemist Dmitri Mendeleev, who had developed the periodic table. In nearly all our experiments discovering transuranium elements, we'd depended on his method of predicting chemical properties based on the element's position in the table. But in the middle of the Cold War, naming an element for a Russian was a somewhat bold gesture that did not sit well with some American critics.<ref>[http://www.vanderkrogt.net/elements/element.php?sym=Md 101. Mendelevium – Elementymology & Elements Multidict]. Peter van der Krogt.</ref>|Glenn T. Seaborg}}

Being the first of the second hundred of the chemical elements, it was decided that the element would be named "mendelevium" after the Russian chemist [[Dmitri Mendeleev]], father of the [[periodic table]]. Because this discovery came during the [[Cold War]], Seaborg had to request permission of the government of the [[United States]] to propose that the element be named for a Russian, but it was granted.<ref name="Choppin" /> {{anchor|rename}}The name "mendelevium" was accepted by the [[International Union of Pure and Applied Chemistry]] (IUPAC) in 1955 with symbol "Mv",<ref>{{cite book |title=Comptes rendus de la confèrence IUPAC|date=1955|url=https://books.google.com/books?id=WJhYAAAAYAAJ |last1=Chemistry |first1=International Union of Pure and Applied}}</ref> which was changed to "Md" in the next IUPAC General Assembly (Paris, 1957).<ref>{{cite book |title=Comptes rendus de la confèrence IUPAC|date=1957|url=https://books.google.com/books?id=f5hYAAAAYAAJ |last1=Chemistry |first1=International Union of Pure and Applied}}</ref>