Introduction to superheavy elements: Difference between revisions

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The beam passes through the target and reaches the next chamber, the separator; if a new nucleus is produced, it is carried with this beam.<ref name="SHEhowvideo">{{Cite web|url=https://www.scientificamerican.com/article/how-to-make-superheavy-elements-and-finish-the-periodic-table-video/|title=How to Make Superheavy Elements and Finish the Periodic Table [Video]|author=Chemistry World|date=2016|website=[[Scientific American]]|language=en|url-status=live|access-date=2020-01-27}}</ref> In the separator, the newly produced nucleus is separated from other nuclides (that of the original beam and any other reaction products){{Efn|This separation is based on that the resulting nuclei move past the target more slowly then the unreacted beam nuclei. The separator contains electric and magnetic fields whose effects on a moving particle cancel out for a specific velocity of a particle.{{sfn|Hoffman|2000|p=334}} Such separation can also be aided by a [[Time-of-flight mass spectrometry|time-of-flight measurement]] and a recoil energy measurement; a combination of the two may allow to estimate the mass of a nucleus.{{sfn|Hoffman|2000|p=335}}}} and transferred to a [[Semiconductor detector|surface-barrier detector]], which stops the nucleus. The exact ___location of the upcoming impact on the detector is marked; also marked are its energy and the time of the arrival.<ref name="SHEhowvideo" /> The transfer takes about 10⁻⁶&nbsp;seconds; in order to be detected, the nucleus must survive this long.{{sfn|Zagrebaev|2013|page=3}} The nucleus is recorded again once its decay is registered, and the ___location, the [[Decay energy|energy]], and the time of the decay are measured.<ref name="SHEhowvideo" />

Stability of a nucleus is provided by the strong interaction. However, its range is very short; as nuclei become larger, its influence on the outermost [[nucleon]]s ([[proton]]s and neutrons) weakens. At the same time, the nucleus is torn apart by electrostatic repulsion between protons, as it has unlimited range.{{sfn|Beiser|2003|p=432}} Superheavy nuclei are thus theoretically predicted<ref>{{Cite journal|last=Staszczak|first=A.|last2=Baran|first2=A.|last3=Nazarewicz|first3=W.|date=2013|title=Spontaneous fission modes and lifetimes of superheavy elements in the nuclear density functional theory|url=|journal=Physical Review C|volume=87|issue=2|pagepages=024320–1|doi=10.1103/physrevc.87.024320|arxiv=1208.1215|bibcode=2013PhRvC..87b4320S|issn=0556-2813}}</ref> and have so far been observed{{sfn|Audi|2017|pp=030001&#45;129–030001&#45;138}} to predominantly decay via decay modes that are caused by such repulsion: [[alpha decay]] and [[spontaneous fission]].{{efn|Not all decay modes are caused by electrostatic repulsion. For example, [[beta decay]] is caused by the [[weak interaction]].{{sfn|Beiser|2003|p=439}}}} Alpha decays are registered by the emitted [[alpha particle]]s, and the decay products are easy to determine before the actual decay; if such a decay or a series of consecutive decays produces a known nucleus, the original product of a reaction can be easily determined.{{efn|Since mass of a nucleus is not measured directly but is rather calculated from that of another nucleus, such measurement is called indirect. Direct measurements are also possible, but for the most part they have remained unavailable for superheavy nuclei.<ref>{{Cite journal|last=Oganessian|first=Yu. Ts.|last2=Rykaczewski|first2=K. P.|date=2015|title=A beachhead on the island of stability|journal=[[Physics Today]]|volume=68|issue=8|pages=32–38|doi=10.1063/PT.3.2880|bibcode=2015PhT....68h..32O|osti=1337838|issn=0031-9228|url=https://www.osti.gov/biblio/1337838}}</ref> The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.<ref>{{Cite journal|last=Grant |first=A.|date=2018|title=Weighing the heaviest elements|journal=Physics Today|language=EN|doi=10.1063/PT.6.1.20181113a}}</ref> Mass was determined from the ___location of a nucleus after the transfer (the ___location helps determine its trajectory, which is linked to the mass-to-charge ratio of the nucleus, since the transfer was done in presence of a magnet).<ref name="C&EN">{{Cite web|url=https://cen.acs.org/physical-chemistry/periodic-table/IYPT-Exploring-the-superheavy-elements-at-the-end-of-the-periodic-table/97/i21|title=Exploring the superheavy elements at the end of the periodic table|last=Howes|first=L.|date=2019|website=[[Chemical & Engineering News]]|language=en|url-status=live|archive-url=|archive-date=|access-date=2020-01-27}}</ref>}} Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.{{Efn|Spontaneous fission was discovered by Soviet physicist [[Georgy Flerov]],<ref name=Distillations>{{Cite journal|last=Robinson|first=A. E.|url=https://www.sciencehistory.org/distillations/the-transfermium-wars-scientific-brawling-and-name-calling-during-the-cold-war|title=The Transfermium Wars: Scientific Brawling and Name-Calling during the Cold War|date=2019|journal=[[Distillations (magazine)|Distillations]]|language=en|access-date=2020-02-22}}</ref> a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.<ref name="coldfusion77">{{Cite web|url=http://n-t.ru/ri/ps/pb106.htm|title=Популярная библиотека химических элементов. Сиборгий (экавольфрам)|trans-title=Popular library of chemical elements. Seaborgium (eka-tungsten)|language=ru|website=n-t.ru|access-date=2020-01-07}} Reprinted from {{cite book|author=<!--none-->|date=1977|title=Популярная библиотека химических элементов. Серебро — Нильсборий и далее|chapter=Экавольфрам|trans-title=Popular library of chemical elements. Silver through nielsbohrium and beyond|trans-chapter=Eka-tungsten|language=ru|publisher=[[Nauka (publisher)|Nauka]]}}</ref> In contrast, the LBL scientists believed fission information was not sufficient for a claim of synthesis of an element. They believed spontaneous fission had not been studied enough to use it for identification of a new element, since there was a difficulty of establishing that a compound nucleus had only ejected neutrons and not charged particles like protons or alpha particles.<ref name=BerkeleyNoSF>{{Cite journal|last=Hyde|first=E. K.|last2=Hoffman|first2=D. C.|authorlink2=Darleane C. Hoffman|last3=Keller|first3=O. L.|date=1987|title=A History and Analysis of the Discovery of Elements 104 and 105|journal=Radiochimica Acta|volume=42|issue=2|doi=10.1524/ract.1987.42.2.57|issn=2193-3405|pages=67–68|url=http://www.escholarship.org/uc/item/05x8w9h7}}</ref> They thus preferred to link new isotopes to the already known ones by successive alpha decays.<ref name=Distillations/>}}

The information available to physicists aiming to synthesize a superheavy element is thus the information collected at the detectors: ___location, energy, and time of arrival of a particle to the detector, and those of its decay. The physicists analyze this data and seek to conclude that it was indeed caused by a new element and could not have been caused by a different nuclide than the one claimed. Often, provided data is insufficient for a conclusion that a new element was definitely created and there is no other explanation for the observed effects; errors in interpreting data have been made.{{Efn|For instance, element&nbsp;102 was mistakenly identified in 1957 at the Nobel Institute of Physics in [[Stockholm]], [[Stockholm County]], [[Sweden]].<ref name=RSC>{{Cite web|url=https://www.rsc.org/periodic-table/element/102/nobelium|title=Nobelium - Element information, properties and uses {{!}} Periodic Table|website=[[Royal Society of Chemistry]]|access-date=2020-03-01}}</ref> There were no earlier definitive claims of creation of this element, and the element was assigned a name by its Swedish, American, and British discoverers, ''nobelium''. It was later shown that the identification was incorrect.{{sfn|Kragh|2018|pp=38–39}} The following year, RL was unable to reproduce the Swedish results and announced instead their synthesis of the element; that claim was also disproved later.{{sfn|Kragh|2018|pp=38–39}} JINR insisted that they were the first to create the element and suggested a name of their own for the new element, ''joliotium'';{{sfn|Kragh|2018|p=40}} the Soviet name was also not accepted (JINR later referred to the naming of element&nbsp;102 as "hasty").<ref name="1993 responses">{{Cite journal|year=1993|title=Responses on the report 'Discovery of the Transfermium elements' followed by reply to the responses by Transfermium Working Group|url=https://www.iupac.org/publications/pac/1993/pdf/6508x1815.pdf|url-status=live|journal=Pure and Applied Chemistry|volume=65|issue=8|pages=1815–1824|doi=10.1351/pac199365081815|archiveurl=https://web.archive.org/web/20131125223512/http://www.iupac.org/publications/pac/1993/pdf/6508x1815.pdf|archivedate=25 November 2013|access-date=7 September 2016|last1=Ghiorso|first1=A.|last2=Seaborg|first2=G. T.|authorlink2=Glenn T. Seaborg|last3=Oganessian|first3=Yu. Ts.|last4=Zvara|first4=I|last5=Armbruster|first5=P|last6=Hessberger|first6=F. P|last7=Hofmann|first7=S|last8=Leino|first8=M|last9=Munzenberg|first9=G|last10=Reisdorf|first10=W|last11=Schmidt|first11=K.-H|displayauthors=3}}</ref> The name "nobelium" remained unchanged on account of its widespread usage.<ref name=IUPAC97>{{Cite journal|doi=10.1351/pac199769122471|title=Names and symbols of transfermium elements (IUPAC Recommendations 1997)|date=1997|journal=Pure and Applied Chemistry|volume=69|pages=2471–2474|issue=12|author=Commission on Nomenclature of Inorganic Chemistry|url=http://publications.iupac.org/pac/pdf/1997/pdf/6912x2471.pdf}}</ref>}}</onlyinclude>