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{{Infobox unbibium}}

'''Unbibium''', also known as '''element 122''' or '''eka-thorium''', is a hypothetical [[chemical element]]; it has placeholder symbol '''Ubb''' and [[atomic number]] 122. ''Unbibium'' and ''Ubb'' are the temporary [[Systematic element name|systematic IUPAC name and symbol]] respectively, which are used until the element is discovered, confirmed, and a permanent name is decided upon. In the [[periodic table]] of the elements, it is expected to follow [[unbiunium]] as the second element of the [[superactinides]] and the fourth element of the 8th [[Period (periodic table)|period]]. Similarly to unbiunium, it is expected to fall within the range of the [[island of stability]], potentially conferring additional stability on some isotopes, especially <sup>306</sup>Ubb which is expected to have a [[Magic number (physics)|magic number]] of neutrons (184).

Despite several attempts, unbibium has not yet been synthesized, nor have any naturally occurring isotopes been found to exist. There are currently no plans to attempt to synthesize unbibium. In 2008, it was claimed to have been discovered in natural thorium samples,<ref name=arxiv>{{cite journal|display-authors=3 |last=Marinov |first=A. |author2=Rodushkin, I. |author3=Kolb, D. |author4=Pape, A. |author5=Kashiv, Y. |author6=Brandt, R. |author7=Gentry, R. V. |author8= Miller, H. W. |title=Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th |journal=International Journal of Modern Physics E |volume=19 |pages=131–140 |year=2010 |issue=1 |arxiv= 0804.3869 |bibcode= 2010IJMPE..19..131M |doi= 10.1142/S0218301310014662|s2cid=117956340 }}</ref> but that claim has now been dismissed by recent repetitions of the experiment using more accurate techniques.

Chemically, unbibium is expected to show some resemblance to [[cerium]] and [[thorium]]. However, [[relativistic quantum chemistry|relativistic effects]] may cause some of its properties to differ; for example, it is expected to have a ground state electron configuration of &#91;[[oganesson|Og]]&#93; 7d<sup>1</sup> 8s<sup>2</sup> 8p<sup>1</sup> or [Og] 8s<sup>2</sup> 8p<sup>2</sup>, despite its predicted position in the g-block superactinide series.<ref name="Pyykkö2011" />

==Introduction==
{{Excerpt|Superheavy element|Introduction|subsections=yes}}

==History==
===Synthesis attempts===
====Fusion-evaporation====
Two attempts were made to synthesize unbibium in the 1970s, both propelled by early predictions on the island of stability at ''N''&nbsp;=&nbsp;184 and ''Z''&nbsp;>&nbsp;120,<ref name=superlourds>{{cite journal|last1=Epherre |first1=M.|last2=Stephan|first2=C.|date=1975|title=Les éléments superlourds|language=fr|journal=Le Journal de Physique Colloques|volume=11|issue=36|pages=C5–159–164 |url=https://core.ac.uk/download/pdf/46775464.pdf |doi=10.1051/jphyscol:1975541}}</ref> and in particular whether superheavy elements could potentially be naturally occurring.<ref name="emsley">{{cite book|last=Emsley |first=John |title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|year=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7|page=588}}</ref> The first attempts to synthesize unbibium were performed in 1972 by [[Georgy Flerov|Flerov]] et al. at the [[Joint Institute for Nuclear Research]] (JINR), using the heavy-ion induced hot fusion reactions:<ref name="emsley"/>

:{{nuclide|uranium|238}} + {{nuclide|zinc|66,68}} → {{nuclide|unbibium|304,306}}* → no atoms

Another unsuccessful attempt to synthesize unbibium was carried out in 1978 at the GSI Helmholtz Center, where a natural [[erbium]] target was bombarded with [[xenon-136]] ions:<ref name="emsley"/>

:{{nuclide|erbium|''nat''}} + {{nuclide|xenon|136}} → {{SimpleNuclide|unbibium|298,300,302,303,304,306}}* → no atoms

No atoms were detected and a yield limit of 5&nbsp;[[Barn (unit)|nb]] (5,000&nbsp;[[barn (unit)|pb]]) was measured. Current results (see [[flerovium]]) have shown that the sensitivity of these experiments were too low by at least 3&nbsp;orders of magnitude.<ref name=superlourds/> In particular, the reaction between <sup>170</sup>Er and <sup>136</sup>Xe was expected to yield alpha emitters with half-lives of microseconds that would decay down to isotopes of [[flerovium]] with half-lives perhaps increasing up to several hours, as flerovium is predicted to lie near the center of the island of stability. After twelve hours of irradiation, nothing was found in this reaction. Following a similar unsuccessful attempt to synthesize [[unbiunium]] from <sup>238</sup>U and <sup>65</sup>Cu, it was concluded that half-lives of superheavy nuclei must be less than one microsecond or the cross sections are very small.<ref>{{cite book|last=Hofmann |first=Sigurd|title=On Beyond Uranium: Journey to the End of the Periodic Table|year=2014|publisher=CRC Press |isbn=978-0415284950|page=[https://archive.org/details/onbeyonduraniumj0000hofm/page/105 105] |url=https://archive.org/details/onbeyonduraniumj0000hofm/page/105}}</ref> More recent research into synthesis of superheavy elements suggests that both conclusions are true.<ref name=Karpov /><ref name=Zagrabeav>{{harvnb|Zagrebaev|Karpov|Greiner|2013}}</ref>

In 2000, the [[Gesellschaft für Schwerionenforschung]] (GSI) Helmholtz Center for Heavy Ion Research performed a very similar experiment with much higher sensitivity:<ref name="emsley"/>

:{{nuclide|uranium|238}} + {{nuclide|zinc|70}} → {{nuclide|unbibium|308}}* → no atoms

These results indicate that the synthesis of such heavier elements remains a significant challenge and further improvements of beam intensity and experimental efficiency is required. The sensitivity should be increased to 1&nbsp;[[barn (unit)|fb]] in the future for more quality results.

====Compound nucleus fission====
Several experiments studying the fission characteristics of various superheavy compound nuclei such as <sup>306</sup>Ubb were performed between 2000 and 2004 at the [[Flerov Laboratory of Nuclear Reactions]]. Two nuclear reactions were used, namely <sup>248</sup>Cm + <sup>58</sup>Fe and <sup>242</sup>Pu + <sup>64</sup>Ni.<ref name="emsley"/> The results reveal how superheavy nuclei fission predominantly by expelling [[nuclear shell model|closed shell]] nuclei such as <sup>132</sup>Sn (''Z''&nbsp;=&nbsp;50, ''N''&nbsp;=&nbsp;82). It was also found that the yield for the fusion-fission pathway was similar between <sup>48</sup>Ca and <sup>58</sup>Fe projectiles, suggesting a possible future use of <sup>58</sup>Fe projectiles in superheavy element formation.<ref>see Flerov lab annual reports 2000–2004 inclusive http://www1.jinr.ru/Reports/Reports_eng_arh.html</ref>

===Claimed discovery as a naturally occurring element===
In 2008, a group led by Israeli physicist [[Amnon Marinov]] at the [[Hebrew University of Jerusalem]] claimed to have found single atoms of unbibium-292 in naturally occurring [[thorium]] deposits at an abundance of between 10<sup>−11</sup> and 10<sup>−12</sup> relative to thorium.<ref name=arxiv/> This was the first time in 69 years that a new element had been claimed to be discovered in nature, after [[Marguerite Perey]]'s 1939 discovery of [[francium]].{{efn|Four more elements were discovered after 1939 through synthesis, but were later found to also occur naturally: these were [[promethium]], [[astatine]], [[neptunium]], and [[plutonium]], all of which had been found by 1945.}} The claim of Marinov ''et al.'' was criticized by the scientific community, and Marinov says he has submitted the article to the journals ''[[Nature (journal)|Nature]]'' and ''[[Nature Physics]]'' but both turned it down without sending it for peer review.<ref>{{cite web |url=http://rsc.org/chemistryworld/News/2008/May/02050802.asp |author=Richard Van Noorden |date=2 May 2008 |title=Heaviest element claim criticised |website=Chemical World |access-date=29 September 2009 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304042449/http://rsc.org/chemistryworld/News/2008/May/02050802.asp |url-status=dead }}</ref> The unbibium-292 atoms were claimed to be [[superdeformation|superdeformed]] or [[hyperdeformation|hyperdeformed]] [[nuclear isomer|isomers]], with a half-life of at least 100&nbsp;million years.<ref name="emsley"/>

A criticism of the technique, previously used in purportedly identifying lighter [[thorium]] isotopes by [[mass spectrometry]],<ref name="thorium">{{cite journal |journal=Phys. Rev. C |title=Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes |year=2007 |volume=76 |issue=2 |at=021303(R) |doi=10.1103/PhysRevC.76.021303 |display-authors=3 |first1=A.|last1=Marinov|first2=I. |last2=Rodushkin|first3=Y.|last3=Kashiv |first4=L.|last4=Halicz |first5=I.|last5=Segal|first6=A.|last6=Pape |first7=R. V.|last7=Gentry|first8=H. W.|last8=Miller|first9=D.|last9=Kolb|first10=R.|last10=Brandt |arxiv=nucl-ex/0605008 |bibcode=2007PhRvC..76b1303M|s2cid=119443571 }}</ref> was published in ''[[Physical Review C]]'' in 2008.<ref>{{cite journal |journal=Phys. Rev. C |title=Comment on "Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes"|year=2009|volume=79|issue=4 |at=049801|first1=R. C. |last1=Barber|first2=J. R.|last2=De Laeter|doi=10.1103/PhysRevC.79.049801 |bibcode=2009PhRvC..79d9801B}}</ref> A rebuttal by the Marinov group was published in ''Physical Review C'' after the published comment.<ref>{{cite journal |journal=Phys. Rev. C |title=Reply to "Comment on 'Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes'" |year=2009 |volume=79 |issue=4 |at=049802 |display-authors=3 |first1=A. |last1=Marinov |first2=I. |last2=Rodushkin |first3=Y. |last3=Kashiv |first4=L. |last4=Halicz |first5=I. |last5=Segal |first6=A. |last6=Pape |first7=R. V. |last7=Gentry |first8=H. W. |last8=Miller |first9=D. |last9=Kolb |first10=R. |last10=Brandt |doi=10.1103/PhysRevC.79.049802 |bibcode=2009PhRvC..79d9802M}}</ref>

A repeat of the thorium experiment using the superior method of [[accelerator mass spectrometry]] (AMS) failed to confirm the results, despite a 100-fold better sensitivity.<ref>{{cite journal |journal=Phys. Rev. C |title=Search for long-lived isomeric states in neutron-deficient thorium isotopes |year=2008 |volume=78 |issue=6 |at=064313 |doi=10.1103/PhysRevC.78.064313 |display-authors=3 |first1=J. |last1=Lachner |first2=I. |last2=Dillmann |first3=T. |last3=Faestermann |first4=G. |last4=Korschinek |first5=M. |last5=Poutivtsev |first6=G. |last6=Rugel |bibcode=2008PhRvC..78f4313L |arxiv=0907.0126|s2cid=118655846 }}</ref> This result throws considerable doubt on the results of the Marinov collaboration with regards to their claims of long-lived isotopes of [[thorium]],<ref name="thorium"/> [[roentgenium]],<ref name="roentgenium">{{cite journal |display-authors=3 |last1=Marinov |first1=A. |last2=Rodushkin |first2=I. |last3=Pape |first3=A. |last4=Kashiv |first4=Y. |last5=Kolb |first5=D. |last6=Brandt |first6=R. |last7=Gentry |first7=R. V. |last8=Miller |first8=H. W. |last9=Halicz |first9=L. |first10=I.|last10=Segal|year=2009 |title=Existence of Long-Lived Isotopes of a Superheavy Element in Natural Au |journal=[[International Journal of Modern Physics E]] |volume=18 |number=3 |pages=621–629 |publisher=[[World Scientific]] |arxiv=nucl-ex/0702051 |doi=10.1142/S021830130901280X |url=http://www.phys.huji.ac.il/~marinov/publications/Au_paper_IJMPE_73.pdf |access-date=February 12, 2012 |bibcode=2009IJMPE..18..621M |s2cid=119103410 |url-status=dead |archive-url=https://web.archive.org/web/20140714210340/http://www.phys.huji.ac.il/~marinov/publications/Au_paper_IJMPE_73.pdf |archive-date=2014-07-14}}</ref> and unbibium.<ref name="arxiv"/> Current understanding of superheavy elements indicates that it is very unlikely for any traces of unbibium to persist in natural thorium samples.<ref name="emsley"/>

===Naming===
Using [[Mendeleev's predicted elements|Mendeleev's nomenclature for unnamed and undiscovered elements]], unbibium should instead be known as ''eka-[[thorium]]''.<ref>
{{cite journal |last1=Eliav |first1=Ephraim |last2=Landau |first2=Arie |last3=Ishikawa |first3=Yasuyuki |last4=Kaldor |first4=Uzi |date=26 March 2002 |title=Electronic structure of eka-thorium (element 122) compared with thorium |journal=Journal of Physics B: Atomic, Molecular and Optical Physics |volume=35 |issue=7 |pages=1693–1700 |doi=10.1088/0953-4075/35/7/307|bibcode=2002JPhB...35.1693E |s2cid=250750167 }}</ref> After the [[Systematic element name|recommendations]] of the IUPAC in 1979, the element has since been largely referred to as ''unbibium'' with the atomic symbol of (''Ubb''),<ref name=iupac>{{cite journal|author=Chatt, J.|journal=Pure Appl. Chem.|year=1979|volume=51|pages=381–384|title=Recommendations for the Naming of Elements of Atomic Numbers Greater than 100|doi=10.1351/pac197951020381|issue=2|doi-access=free}}</ref> as its [[Placeholder name|temporary name]] until the element is officially discovered and synthesized, and a permanent name is decided on. Scientists largely ignore this naming convention, and instead simply refer to unbibium as "element&nbsp;122" with the symbol of (''122''), or sometimes even ''E122'' or ''122''.{{sfn|Hoffman|Lee|Pershina|2006|p=[https://archive.org/details/chemistryactinid00katz/page/n2075 1724]}}

==Prospects for future synthesis==
[[File:Superheavy decay modes predicted.png|right|thumb|upright=1.8|Predicted decay modes of superheavy nuclei. The line of synthesized proton-rich nuclei is expected to be broken soon after ''Z''&nbsp;=&nbsp;120, because of the shortening half-lives until around ''Z''&nbsp;=&nbsp;124, the increasing contribution of spontaneous fission instead of alpha decay from ''Z''&nbsp;=&nbsp;122 onward until it dominates from ''Z''&nbsp;=&nbsp;125, and the proton [[nuclear drip line|drip line]] around ''Z''&nbsp;=&nbsp;130. The white ring denotes the expected location of the island of stability; the two squares outlined in white denote <sup>291</sup>[[copernicium|Cn]] and <sup>293</sup>Cn, predicted to be the longest-lived nuclides on the island with half-lives of centuries or millennia.<ref name=Greiner>{{cite journal |last1=Greiner |first1=W |date=2013 |title=Nuclei: superheavy–superneutronic–strange–and of antimatter |url=http://inspirehep.net/record/1221632/files/jpconf13_413_012002.pdf |journal=Journal of Physics: Conference Series |volume=413 |issue=1 |at=012002 |doi=10.1088/1742-6596/413/1/012002 |access-date=30 April 2017 |bibcode=2013JPhCS.413a2002G|doi-access=free }}</ref><ref name=Karpov>{{cite web |title=Superheavy Nuclei: which regions of nuclear map are accessible in the nearest studies |last1=Karpov |first1=A |last2=Zagrebaev |first2=V |last3=Greiner |first3=W |date=2015 |website=cyclotron.tamu.edu |publisher=Texas A & M University |access-date=30 October 2018 |url=http://cyclotron.tamu.edu/she2015/assets/pdfs/presentations/Karpov_SHE_2015_TAMU.pdf}}</ref>]]

Every element from [[mendelevium]] onward was produced in fusion-evaporation reactions, culminating in the discovery of the heaviest known element [[oganesson]] in 2002<ref name="118A">{{cite web |title=Element 118: results from the first {{SimpleNuclide|Californium|249}} + {{SimpleNuclide|Calcium|48}} experiment |last=Oganessian |first=Y. T. |display-authors=etal |publisher=Communication of the Joint Institute for Nuclear Research |date=2002 |url=http://159.93.28.88/linkc/118/anno.html |url-status=dead |archive-url=https://web.archive.org/web/20110722060249/http://159.93.28.88/linkc/118/anno.html |archive-date=22 July 2011}}</ref><ref>{{cite press release|title=Livermore scientists team with Russia to discover element 118|url=https://www.llnl.gov/news/newsreleases/2006/NR-06-10-03.html|publisher=Livermore|date=3 December 2006|access-date=18 January 2008|archive-date=17 October 2011|archive-url=https://web.archive.org/web/20111017105348/https://www.llnl.gov/news/newsreleases/2006/NR-06-10-03.html|url-status=dead}}</ref> and most recently [[tennessine]] in 2010.<ref name=117disc>{{cite journal|last1=Oganessian|first1=Y. T.|last2=Abdullin|first2=F.|last3=Bailey|first3=P. D.|display-authors=etal |date=April 2010|title=Synthesis of a New Element with Atomic Number 117 |journal=Physical Review Letters |volume=104|issue=14|at=142502 |bibcode=2010PhRvL.104n2502O |doi=10.1103/PhysRevLett.104.142502 |format=PDF |url=https://www.researchgate.net/publication/44610795 |pmid=20481935|doi-access=free}}</ref> These reactions approached the limit of current technology; for example, the synthesis of tennessine required 22 milligrams of <sup>249</sup>Bk and an intense <sup>48</sup>Ca beam for six months. The intensity of beams in superheavy element research cannot exceed 10<sup>12</sup> projectiles per second without damaging the target and detector, and producing larger quantities of increasingly rare and unstable [[actinide]] targets is impractical.<ref name=Roberto>{{cite web |title=Actinide Targets for Super-Heavy Element Research |last=Roberto |first=J. B. |date=2015 |website=cyclotron.tamu.edu |publisher=Texas A & M University |access-date=30 October 2018 |url=http://cyclotron.tamu.edu/she2015/assets/pdfs/presentations/Roberto_SHE_2015_TAMU.pdf}}</ref>
Consequently, future experiments must be done at facilities such as the superheavy element factory (SHE-factory) at the [[Joint Institute for Nuclear Research]] (JINR) or [[RIKEN]], which will allow experiments to run for longer stretches of time with increased detection capabilities and enable otherwise inaccessible reactions.<ref>{{cite web |title=平成23年度 研究業績レビュー（中間レビュー）の実施について |language=ja |trans-title=Implementation of the 2011 Research Achievement Review (Interim Review) |last1=Hagino |first1=Kouichi |last2=Hofmann |first2=Sigurd |last3=Miyatake |first3=Hiroari |last4=Nakahara |first4=Hiromichi |date=July 2012 |website=www.riken.jp |publisher=RIKEN |access-date=5 May 2017 |url= http://www.riken.jp/~/media/riken/about/reports/evaluation/rnc/rep/rnc-morita2012-report-e.pdf |archive-url=https://web.archive.org/web/20190330183221/http://www.riken.jp/~/media/riken/about/reports/evaluation/rnc/rep/rnc-morita2012-report-e.pdf |archive-date=2019-03-30 |url-status=dead}}</ref>

It is possible that fusion-evaporation reactions will not be suitable for the discovery of unbibium or heavier elements. Various models predict increasingly short [[Alpha decay|alpha]] and [[spontaneous fission]] half-lives for isotopes with ''Z''&nbsp;=&nbsp;122 and ''N''&nbsp;~&nbsp;180 on the order of microseconds or less,<ref name=CN14>{{cite web|url=https://wwwndc.jaea.go.jp/CN14/ |title=Chart of the Nuclides |last1=Koura|first1=H. |last2=Katakura|first2=J|last3=Tachibana|first3=T |last4=Minato|first4=F |date=2015|publisher=Japan Atomic Energy Agency|access-date=30 October 2018}}</ref> rendering detection nearly impossible with current equipment.<ref name=Karpov /> The increasing dominance of spontaneous fission also may sever possible ties to known nuclei of livermorium or oganesson and make identification and confirmation more difficult; a similar problem occurred in the road to confirmation of the decay chain of <sup>294</sup>Og which has no anchor to known nuclei.<ref>{{cite journal|doi=10.1351/PAC-REP-10-05-01 |title=Discovery of the elements with atomic numbers greater than or equal to 113 (IUPAC Technical Report) |date=2011|last1=Barber|first1=R. C. |last2=Karol|first2=P. J. |last3=Nakahara|first3=H. |last4=Vardaci |first4=E. |last5=Vogt|first5=E. W. |journal=Pure and Applied Chemistry|volume=83|issue=7 |page=1|doi-access=free}}</ref> For these reasons, other methods of production may need to be researched such as multi-nucleon transfer reactions capable of populating longer-lived nuclei. A similar switch in experimental technique occurred when hot fusion using <sup>48</sup>Ca projectiles was used instead of cold fusion (in which cross sections decrease rapidly with increasing atomic number) to populate elements with ''Z''&nbsp;>&nbsp;113.<ref name=Zagrabeav />

Nevertheless, several fusion-evaporation reactions leading to unbibium have been proposed in addition to those already tried unsuccessfully, though no institution has immediate plans to make synthesis attempts, instead focusing first on elements 119, 120, and possibly 121. Because cross sections increase with asymmetry of the reaction,<ref name=Zagrabeav /> a [[chromium]] beam would be most favorable in combination with a [[californium]] target,<ref name=Karpov /> especially if the predicted closed neutron shell at ''N''&nbsp;=&nbsp;184 could be reached in more neutron-rich products and confer additional stability. In particular, the reaction between {{nuclide|Cr|54}} and {{nuclide|Cf|252}} would generate the compound nucleus {{nuclide|Ubb|306}} and reach the shell at ''N''&nbsp;=&nbsp;184, though the analogous reaction with a {{nuclide|Cf|249}} target is believed to be more feasible because of the presence of unwanted [[fission product]]s from {{nuclide|Cf|252}} and difficulty in accumulating the required amount of target material.<ref name=Ghahramany>{{cite journal|last1=Ghahramany |first1=N. |last2=Ansari |first2=A. |date=September 2016|title=Synthesis and decay process of superheavy nuclei with Z&nbsp;=&nbsp;119-122 via hot fusion reactions|journal=European Physical Journal A|volume=52|issue=287|page=287 |doi=10.1140/epja/i2016-16287-6 |bibcode=2016EPJA...52..287G |s2cid=125102374 |url=https://www.researchgate.net/publication/308276903 |format=PDF}}</ref> One possible synthesis of unbibium could occur as follows:<ref name=Karpov />

:{{nuclide|californium|249}} + {{nuclide|chromium|54}} → {{nuclide|unbibium|300}} + 3 {{su|b=0|p=1}}{{SubatomicParticle|neutron}}

Should this reaction be successful and alpha decay remain dominant over spontaneous fission, the resultant <sup>300</sup>Ubb would decay through <sup>296</sup>Ubn which may be populated in cross-bombardment between <sup>249</sup>Cf and <sup>50</sup>Ti. Although this reaction is one of the most promising options for the synthesis of unbibium in the near future, the maximum cross section is predicted to be 3&nbsp;[[barn (unit)|fb]],<ref name=Ghahramany /> one order of magnitude lower than the lowest measured cross section in a successful reaction. The more symmetrical reactions <sup>244</sup>Pu + <sup>64</sup>Ni and <sup>248</sup>Cm + <sup>58</sup>Fe<ref name=Karpov /> have also been proposed and may produce more neutron-rich isotopes. With increasing atomic number, one must also be aware of decreasing [[fission barrier]] heights, resulting in lower survival probability of [[compound nucleus|compound nuclei]], especially above the predicted magic numbers at ''Z''&nbsp;=&nbsp;126 and ''N''&nbsp;=&nbsp;184.<ref name=Ghahramany />

==Predicted properties==
===Nuclear stability and isotopes===
{{see also|Island of stability}}
[[File:Island of Stability derived from Zagrebaev.svg|thumb|upright=2.75|alt=A 2D graph with rectangular cells colored in black-and-white colors, spanning from the llc to the urc, with cells mostly becoming lighter closer to the latter|A chart of nuclide stability as used by the Dubna team in 2010. Characterized isotopes are shown with borders. Beyond element&nbsp;118 (oganesson, the last known element), the line of known nuclides is expected to rapidly enter a region of instability, with no half-lives over one microsecond after [[unbiunium|element&nbsp;121]]; this poses difficulties in identifying heavier elements such as unbibium. The elliptical region encloses the predicted location of the island of stability.<ref name=Zagrabeav />]]

The stability of nuclei decreases greatly with the increase in atomic number after [[plutonium]], the heaviest [[primordial element]], so that all isotopes with an atomic number above [[mendelevium|101]] [[radioactive decay|decay radioactively]] with a [[half-life]] under a day. No elements with [[atomic number]]s above 82 (after [[lead]]) have stable isotopes.<ref>{{cite journal|author1=Pierre de Marcillac |author2=Noël Coron |author3=Gérard Dambier |author4=Jacques Leblanc |author5=Jean-Pierre Moalic |date=April 2003|title= Experimental detection of α-particles from the radioactive decay of natural bismuth|journal= Nature|volume= 422|pages= 876–878|pmid=12712201|doi= 10.1038/nature01541|issue= 6934|bibcode= 2003Natur.422..876D|s2cid=4415582 }}</ref> Nevertheless, because of [[magic number (physics)|reasons]] not very well understood yet, there is a slight increased nuclear stability around atomic numbers [[darmstadtium|110]]–[[flerovium|114]], which leads to the appearance of what is known in nuclear physics as the "[[island of stability]]". This concept, proposed by [[University of California, Berkeley|University of California]] professor [[Glenn Seaborg]], explains why [[superheavy element]]s last longer than predicted.<ref>{{cite book|title=Van Nostrand's scientific encyclopedia|first1=Glenn D. |last1=Considine |first2=Peter H. |last2=Kulik |publisher=Wiley-Interscience |year=2002|edition=9|isbn=978-0-471-33230-5|oclc=223349096}}</ref>

In this region of the periodic table, ''N''&nbsp;=&nbsp;184 has been suggested as a [[nuclear shell model|closed neutron shell]], and various atomic numbers have been proposed as closed proton shells, such as ''Z''&nbsp;=&nbsp;114, 120, 122, 124, and 126. The island of stability would be characterized by longer half-lives of nuclei located near these magic numbers, though the extent of stabilizing effects is uncertain due to predictions of weakening of the proton shell closures and possible loss of [[doubly magic|double magicity]].<ref name=magickoura>{{cite journal|last1=Koura|first1=H.|last2=Chiba|first2=S. |date=2013|title=Single-Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region|journal=Journal of the Physical Society of Japan|volume=82|issue=1 |at=014201|doi=10.7566/JPSJ.82.014201 |bibcode=2013JPSJ...82a4201K |url=https://www.researchgate.net/publication/258799250}}</ref> More recent research predicts the island of stability to instead be centered at [[Beta-decay stable isobars|beta-stable]] [[copernicium]] isotopes <sup>291</sup>Cn and <sup>293</sup>Cn,<ref name=Zagrabeav /><ref name=Palenzuela /> which would place unbibium well above the island and result in short half-lives regardless of shell effects. The increased stability of elements&nbsp;112–118 has also been attributed to the [[oblate spheroid|oblate]] shape of such nuclei and resistance to spontaneous fission. The same model also proposes <sup>306</sup>Ubb as the next spherical doubly magic nucleus, thus defining the true island of stability for spherical nuclei.<ref name=Kratz>{{cite conference |last1=Kratz |first1=J. V. |date=5 September 2011 |title=The Impact of Superheavy Elements on the Chemical and Physical Sciences |url=http://tan11.jinr.ru/pdf/06_Sep/S_1/02_Kratz.pdf |conference=4th International Conference on the Chemistry and Physics of the Transactinide Elements |access-date=27 August 2013}}</ref>

[[File:IBA nuclear shells.svg|thumb|upright=1.4|Regions of differently shaped nuclei, as predicted by the [[Interacting Boson Approximation]]<ref name=Kratz/>]]

A quantum tunneling model predicts the alpha-decay half-lives of unbibium isotopes <sup>284–322</sup>Ubb to be on the order of microseconds or less for all isotopes lighter than <sup>315</sup>Ubb,<ref>{{cite journal|journal=[[Atomic Data and Nuclear Data Tables]] |volume=94|pages=781–806|date=2008|title=Nuclear half-lives for α -radioactivity of elements with 100 ≤ Z ≤ 130|author=Chowdhury, R. P.|author2=Samanta, C.|author3=Basu, D.N. |doi=10.1016/j.adt.2008.01.003|bibcode=2008ADNDT..94..781C|issue=6|arxiv=0802.4161|s2cid=96718440 }}</ref> highlighting a significant challenge in experimental observation of this element. This is consistent with many predictions, though the exact location of the 1&nbsp;microsecond border varies by model. Additionally, spontaneous fission is expected to become a major decay mode in this region, with half-lives on the order of femtoseconds predicted for some [[Even and odd atomic nuclei#Even proton, even neutron|even–even isotopes]]<ref name=CN14 /> due to minimal hindrance resulting from nucleon pairing and loss of stabilizing effects farther away from magic numbers.<ref name=Ghahramany /> A 2016 calculation on the half-lives and probable decay chains of isotopes <sup>280–339</sup>Ubb yields corroborating results: <sup>280–297</sup>Ubb will be [[Nuclear drip line|proton unbound]] and possibly decay by [[proton emission]], <sup>298–314</sup>Ubb will have alpha half-lives on the order of microseconds, and those heavier than <sup>314</sup>Ubb will predominantly decay by spontaneous fission with short half-lives.<ref name=a128>{{Cite journal |last1=Santhosh|first1=K.P.|last2=Priyanka|first2=B.|last3=Nithya|first3=C.|date=2016 |title=Feasibility of observing the α decay chains from isotopes of SHN with Z&nbsp;=&nbsp;128, Z&nbsp;=&nbsp;126, Z&nbsp;=&nbsp;124 and Z&nbsp;=&nbsp;122|journal=Nuclear Physics A|volume=955 |issue=November 2016|pages=156–180|doi=10.1016/j.nuclphysa.2016.06.010|bibcode=2016NuPhA.955..156S |arxiv=1609.05498|s2cid=119219218}}</ref> For the lighter alpha emitters that may be populated in fusion-evaporation reactions, some long decay chains leading down to known or reachable isotopes of lighter elements are predicted. Additionally, the isotopes <sup>308–310</sup>Ubb are predicted to have half-lives under 1&nbsp;microsecond,<ref name=CN14 /><ref name=a128 /> too short for detection as a result of significantly lower [[nuclear binding energy|binding energy]] for neutron numbers immediately above the ''N''&nbsp;=&nbsp;184 shell closure. Alternatively, a second island of stability with total half-lives of approximately 1&nbsp;second may exist around ''Z''&nbsp;~&nbsp;124 and ''N''&nbsp;~&nbsp;198, though these nuclei will be difficult or impossible to reach using current experimental techniques.<ref name=Palenzuela>{{cite journal|last1=Palenzuela|first1=Y. M.|last2=Ruiz|first2=L. F.|last3=Karpov|first3=A.|last4=Greiner |first4=W.|year=2012|title=Systematic Study of Decay Properties of Heaviest Elements|journal=Bulletin of the Russian Academy of Sciences: Physics|volume=76|issue=11|pages=1165–1171|doi=10.3103/s1062873812110172 |bibcode=2012BRASP..76.1165P |s2cid=120690838|issn=1062-8738 |url=http://nrv.jinr.ru/karpov/publications/Palenzuela12_BRAS.pdf}}</ref> However, these predictions are strongly dependent on the chosen nuclear mass models, and it is unknown which isotopes of unbibium will be most stable. Regardless, these nuclei will be hard to synthesize as no combination of obtainable target and projectile can provide enough neutrons in the compound nucleus. Even for nuclei reachable in fusion reactions, spontaneous fission and possibly also [[cluster decay]]<ref>{{cite journal |last1=Poenaru|first1=Dorin N.|last2=Gherghescu|first2=R. A.|last3=Greiner|first3=W.|date=2012 |title=Cluster decay of superheavy nuclei|journal=Physical Review C |volume=85|issue=3 |page=034615 |doi=10.1103/PhysRevC.85.034615 |url=https://www.researchgate.net/publication/235507943 |access-date=2 May 2017 |bibcode=2012PhRvC..85c4615P }}</ref> might have significant branches, posing another hurdle to identification of superheavy elements as they are normally identified by their successive alpha decays.

===Chemical===
Unbibium is predicted to be similar in chemistry to [[cerium]] and thorium, which likewise have four valence electrons above a noble gas core, although it may be more reactive. Additionally, unbibium is predicted to belong to a new block of [[Valence electron|valence]] g-electron atoms, although the 5g orbital is not expected to start filling until about element 125. The predicted ground-state electron configuration of unbibium is either &#91;[[oganesson|Og]]&#93; 7d<sup>1</sup> 8s<sup>2</sup> 8p<sup>1</sup><ref name="Pyykkö2011"/>{{sfn|Hoffman|Lee|Pershina|2006|p={{pn|date=April 2021}}}} or 8s<sup>2</sup> 8p<sup>2</sup>,<ref name=Umemoto>{{cite journal |last1=Umemoto |first1=Koichiro |last2=Saito |first2=Susumu |date=1996 |title=Electronic Configurations of Superheavy Elements |doi=10.1143/JPSJ.65.3175 |journal=Journal of the Physical Society of Japan |volume=65 |issue=10 |pages=3175–3179 |bibcode=1996JPSJ...65.3175U |url=https://journals.jps.jp/doi/pdf/10.1143/JPSJ.65.3175 |access-date=31 January 2021|url-access=subscription }}</ref> in contrast to the expected &#91;[[oganesson|Og]]&#93; 5g<sup>2</sup> 8s<sup>2</sup> in which the 5g orbital starts filling at element 121. (The ds<sup>2</sup>p and s<sup>2</sup>p<sup>2</sup> configurations are expected to be only separated by about 0.02&nbsp;eV.)<ref name=Umemoto/> In the superactinides, [[Relativistic quantum chemistry|relativistic effects]] might cause a breakdown of the [[Aufbau principle]] and create overlapping of the 5g, 6f, 7d and 8p orbitals;<ref name=EB>{{cite web|author=Seaborg|date=c. 2006|title=transuranium element (chemical element) |url=http://www.britannica.com/EBchecked/topic/603220/transuranium-element |publisher=Encyclopædia Britannica |access-date=2010-03-16}}</ref> experiments on the chemistry of [[copernicium]] and [[flerovium]] provide strong indications of the increasing role of relativistic effects. As such, the chemistry of elements following unbibium becomes more difficult to predict.

Unbibium would most likely form a dioxide, Ubb[[Oxygen|O]]<sub>2</sub>, and tetrahalides, such as Ubb[[Fluorine|F]]<sub>4</sub> and Ubb[[Chlorine|Cl]]<sub>4</sub>.<ref name="Pyykkö2011" /> The main oxidation state is predicted to be +4, similar to cerium and thorium.<ref name="emsley"/> A first ionization energy of 5.651 [[electronvolt|eV]] and second ionization energy of 11.332 eV are predicted for unbibium; this and other calculated ionization energies are lower than the analogous values for thorium, suggesting that unbibium will be more reactive than thorium.{{sfn|Hoffman|Lee|Pershina|2006|p={{pn|date=April 2021}}}}<ref name=Eliav1/>
{{clear}}

==Notes==
{{Notelist}}

==References==
{{Reflist|refs=

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<ref name=Eliav1>{{cite journal|last=Eliav|first=E.|last2=Fritzsche|first2=S.|last3=Kaldor|first3=U. |date=2015|title=Electronic structure theory of the superheavy elements|journal=Nuclear Physics A |volume=944|issue=December 2015 |pages=518–550|doi=10.1016/j.nuclphysa.2015.06.017 |url= https://www.researchgate.net/publication/279634737_Electronic_structure_theory_of_the_superheavy_elements}}</ref>
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==External links==
*[https://web.archive.org/web/20080603153643/http://www.chemistry-blog.com/2008/04/29/adressing-marinovs-element-122-claim/ Chemistry-Blog: Independent analysis of Marinov's 122 claim]
*[https://wwwndc.jaea.go.jp/CN14/ Chart of the Nuclides 2014]

{{Extended periodic table (by Fricke, 32 columns, compact)}}

[[Category:Unbibium| ]]
[[Category:Hypothetical chemical elements|122]]