Island of stability

{{see also|Valley of stability}}

File:Isotopes and half-life.svg

The composition of a nuclide (atomic nucleus) is defined by the number of protons Z and the number of neutrons N, which sum to mass number A. Proton number Z, also named the atomic number, determines the position of an element in the periodic table. The approximately 3300 known nuclides{{cite web |last=Thoennessen |first=M. |title=Discovery of Nuclides Project |url=https://people.nscl.msu.edu/~thoennes/isotopes/index.html |date=2018 |access-date=13 September 2019}} are commonly represented in a chart with Z and N for its axes and the half-life for radioactive decay indicated for each unstable nuclide (see figure).{{harvnb|Podgorsak|2016|p=512}} {{As of|2019}}, 251 nuclides are observed to be stable (having never been observed to decay);{{cite web |date=2017 |title=Atomic structure |url=https://www.arpansa.gov.au/understanding-radiation/what-is-radiation/ionising-radiation/atomic-structure |website=Australian Radiation Protection and Nuclear Safety Agency |publisher=Commonwealth of Australia |access-date=16 February 2019}} generally, as the number of protons increases, stable nuclei have a higher neutron–proton ratio (more neutrons per proton). The last element in the periodic table that has a stable isotope is lead (Z = 82),{{efn|The heaviest stable element was believed to be bismuth (atomic number 83) until 2003, when its only stable isotope, ²⁰⁹Bi, was observed to undergo alpha decay.{{cite journal|last1 = Marcillac|first1 = P.|last2=Coron |first2=N. |last3=Dambier |first3=G. |last4=Leblanc |first4=J. |last5=Moalic |first5=J.-P. |date=2003 |display-authors=3 |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}}}}{{efn|It is theoretically possible for other observationally stable nuclides to decay, though their predicted half-lives are so long that this process has never been observed.{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |display-authors=3 |title=Experimental searches for rare alpha and beta decays |journal=European Physical Journal A |date=2019 |volume=55 |issue=8 |pages=140-1–140-7 |doi=10.1140/epja/i2019-12823-2 |issn=1434-601X |arxiv=1908.11458|bibcode=2019EPJA...55..140B |s2cid=201664098 }}}} with stability (i.e., half-lives of the longest-lived isotopes) generally decreasing in heavier elements,{{efn|1=A region of increased stability encompasses thorium (Z = 90) and uranium (Z = 92) whose half-lives are comparable to the age of the Earth. Elements intermediate between bismuth and thorium have shorter half-lives, and heavier nuclei beyond uranium become more unstable with increasing atomic number.}}{{cite journal |last=Greiner |first=W. |date=2012 |title=Heavy into Stability |journal=Physics |volume=5 |pages=115-1–115-3 |doi=10.1103/Physics.5.115|bibcode=2012PhyOJ...5..115G |doi-access=free }} especially beyond curium (Z = 96).{{cite journal |last1=Terranova |first1=M. L. |last2=Tavares |first2=O. A. P. |date=2022 |title=The periodic table of the elements: the search for transactinides and beyond |journal=Rendiconti Lincei. Scienze Fisiche e Naturali |volume=33 |issue=1 |pages=1–16 |doi=10.1007/s12210-022-01057-w|bibcode=2022RLSFN..33....1T |s2cid=247111430 |doi-access=free }} The half-lives of nuclei also decrease when there is a lopsided neutron–proton ratio, such that the resulting nuclei have too few or too many neutrons to be stable.{{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=12 April 2019}}

The stability of a nucleus is determined by its binding energy, higher binding energy conferring greater stability. The binding energy per nucleon increases with atomic number to a broad plateau around A = 60, then declines.{{harvnb|Podgorsak|2016|p=33}} If a nucleus can be split into two parts that have a lower total energy (a consequence of the mass defect resulting from greater binding energy), it is unstable. The nucleus can hold together for a finite time because there is a potential barrier opposing the split, but this barrier can be crossed by quantum tunneling. The lower the barrier and the masses of the fragments, the greater the probability per unit time of a split.{{cite book |last1=Blatt |first1=J. M. |last2=Weisskopf |first2=V. F. |title=Theoretical nuclear physics |date=2012 |publisher=Dover Publications |isbn=978-0-486-13950-0 |pages=7–9}}

Protons in a nucleus are bound together by the strong force, which counterbalances the Coulomb repulsion between positively charged protons. In heavier nuclei, larger numbers of uncharged neutrons are needed to reduce repulsion and confer additional stability. Even so, as physicists started to synthesize elements that are not found in nature, they found the stability decreased as the nuclei became heavier.{{cite news |last1=Sacks |first1=O. |title=Greetings From the Island of Stability |url=https://www.nytimes.com/2004/02/08/opinion/greetings-from-the-island-of-stability.html |access-date=16 February 2019 |work=The New York Times |date=2004 |url-status=dead |archive-url=https://web.archive.org/web/20180704182825/https://www.nytimes.com/2004/02/08/opinion/greetings-from-the-island-of-stability.html |archive-date=4 July 2018}} Thus, they speculated that the periodic table might come to an end. The discoverers of plutonium (element 94) considered naming it "ultimium", thinking it was the last.{{harvnb|Hoffman|2000|p=34}} Following the discoveries of heavier elements, of which some decayed in microseconds, it then seemed that instability with respect to spontaneous fission would limit the existence of heavier elements. In 1939, an upper limit of potential element synthesis was estimated around element 104, and following the first discoveries of transactinide elements in the early 1960s, this upper limit prediction was extended to element 108.

File:Next proton shell.svgAs early as 1914, the possible existence of superheavy elements with atomic numbers well beyond that of uranium—then the heaviest known element—was suggested, when German physicist Richard Swinne proposed that superheavy elements around Z = 108 were a source of radiation in cosmic rays. Although he did not make any definitive observations, he hypothesized in 1931 that transuranium elements around Z = 100 or Z = 108 may be relatively long-lived and possibly exist in nature.{{harvnb|Kragh|2018|pages=9–10}} In 1955, American physicist John Archibald Wheeler also proposed the existence of these elements;{{harvnb|Hoffman|2000|p=400}} he is credited with the first usage of the term "superheavy element" in a 1958 paper published with Frederick Werner.{{cite report |last1=Thompson |first1=S. G. |last2=Tsang |first2=C. F. |title=Superheavy elements |date=1972 |publisher=Lawrence Berkeley National Laboratory |id=LBL-665 |page=28 |url=https://escholarship.org/content/qt4qh151mc/qt4qh151mc.pdf}} This idea did not attract wide interest until a decade later, after improvements in the nuclear shell model. In this model, the atomic nucleus is built up in "shells", analogous to electron shells in atoms. Independently of each other, neutrons and protons have energy levels that are normally close together, but after a given shell is filled, it takes substantially more energy to start filling the next. Thus, the binding energy per nucleon reaches a local maximum and nuclei with filled shells are more stable than those without.{{cite web |last=Nave |first=R. |title=Shell Model of Nucleus |work=HyperPhysics |publisher=Department of Physics and Astronomy, Georgia State University |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Nuclear/shell.html |access-date=22 January 2007 }} This theory of a nuclear shell model originates in the 1930s, but it was not until 1949 that German physicists Maria Goeppert Mayer and Johannes Hans Daniel Jensen et al. independently devised the correct formulation.{{cite journal |last1=Caurier |first1=E. |last2=Martínez-Pinedo |first2=G. |last3=Nowacki |first3=F. |last4=Poves |first4=A. |last5=Zuker |first5=A. P. |display-authors=3 |date=2005 |title=The shell model as a unified view of nuclear structure |journal=Reviews of Modern Physics |volume=77 |issue=2 |page=428 |doi=10.1103/RevModPhys.77.427 |arxiv=nucl-th/0402046|bibcode=2005RvMP...77..427C |s2cid=119447053 }}

The numbers of nucleons for which shells are filled are called magic numbers. Magic numbers of 2, 8, 20, 28, 50, 82 and 126 have been observed for neutrons, and the next number is predicted to be 184.{{cite book |last1=Satake |first1=M. |title=Introduction to nuclear chemistry. |date=2010 |publisher=Discovery Publishing House |isbn=978-81-7141-277-8 |page=36}} Protons share the first six of these magic numbers,{{cite book |last1=Ebbing |first1=D. |last2=Gammon |first2=S. D. |title=General chemistry |date=2007 |publisher=Houghton Mifflin |isbn=978-0-618-73879-3 |page=858 |edition=8th}} and 126 has been predicted as a magic proton number since the 1940s.{{harvnb|Kragh|2018|p=22}} Nuclides with a magic number of each—such as ¹⁶O (Z = 8, N = 8), ¹³²Sn (Z = 50, N = 82), and ²⁰⁸Pb (Z = 82, N = 126)—are referred to as "doubly magic" and are more stable than nearby nuclides as a result of greater binding energies.{{cite news |last1=Dumé |first1=B. |title="Magic" numbers remain magic |url=https://physicsworld.com/a/magic-numbers-remain-magic/ |access-date=17 February 2019 |work=Physics World |publisher=IOP Publishing |date=2005}}{{cite journal |last1=Blank |first1=B. |last2=Regan |first2=P. H. |title=Magic and Doubly-Magic Nuclei |date=2000 |journal=Nuclear Physics News |volume=10 |issue=4 |pages=20–27 |url=https://www.researchgate.net/publication/232899048 |doi=10.1080/10506890109411553|s2cid=121966707 }}

In the late 1960s, more sophisticated shell models were formulated by American physicist William Myers and Polish physicist Władysław Świątecki, and independently by German physicist Heiner Meldner (1939–2019{{cite web |url=https://www.llnl.gov/community/retiree-and-employee-resources/in-memoriam/heiner-walter-meldner |title=Heiner Walter Meldner |publisher=Lawrence Livermore National Laboratory |date=2019}}{{cite web |url=https://www.legacy.com/obituaries/sandiegouniontribune/obituary.aspx?n=heiner-walter-meldner&pid=193040302 |title=Heiner Meldner Obituary |date=2019 |publisher=The San Diego Union-Tribune |website=Legacy.com}}). With these models, taking into account Coulomb repulsion, Meldner predicted that the next proton magic number may be 114 instead of 126.{{cite journal |last1=Bemis |first1=C. E. |last2=Nix |first2=J. R. |date=1977 |title=Superheavy elements – the quest in perspective |journal=Comments on Nuclear and Particle Physics |volume=7 |issue=3 |pages=65–78 |url=http://inspirehep.net/record/1382449/files/v7-n3-p65.pdf |issn=0010-2709}} Myers and Świątecki appear to have coined the term "island of stability", and American chemist Glenn Seaborg, later a discoverer of many of the superheavy elements, quickly adopted the term and promoted it.{{cite arXiv |title=The Search for Superheavy Elements: Historical and Philosophical Perspectives |pages=8–9 |eprint=1708.04064 |date=2017|last1=Kragh |first1=H.|class=physics.hist-ph }} Myers and Świątecki also proposed that some superheavy nuclei would be longer-lived as a consequence of higher fission barriers. Further improvements in the nuclear shell model by Soviet physicist Vilen Strutinsky led to the emergence of the macroscopic–microscopic method, a nuclear mass model that takes into consideration both smooth trends characteristic of the liquid drop model and local fluctuations such as shell effects. This approach enabled Swedish physicist Sven Nilsson et al., as well as other groups, to make the first detailed calculations of the stability of nuclei within the island. With the emergence of this model, Strutinsky, Nilsson, and other groups argued for the existence of the doubly magic nuclide ²⁹⁸Fl (Z = 114, N = 184), rather than ³¹⁰Ubh (Z = 126, N = 184) which was predicted to be doubly magic as early as 1957. Subsequently, estimates of the proton magic number have ranged from 114 to 126, and there is still no consensus.{{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|pages=014201-1–014201-5|url=https://www.researchgate.net/publication/258799250 |doi=10.7566/JPSJ.82.014201|bibcode=2013JPSJ...82a4201K}}{{cite magazine |url=https://www.science.org/content/article/hopes-evaporate-superheavy-element-flerovium-having-long-life |last=Clery |first=D. |title=Hopes evaporate for the superheavy element flerovium having a long life |journal=Science |date=2021 |doi=10.1126/science.abh0581}}

Interest in a possible island of stability grew throughout the 1960s, as some calculations suggested that it might contain nuclides with half-lives of billions of years.{{harvnb|Lodhi|1978|p=11}}{{cite journal |last=Oganessian |first=Yu. Ts. |year=2012 |title=Nuclei in the "Island of Stability" of Superheavy Elements |journal=Journal of Physics: Conference Series |volume=337 |issue=1 |page=012005 |bibcode=2012JPhCS.337a2005O |doi=10.1088/1742-6596/337/1/012005|doi-access=free }} They were also predicted to be especially stable against spontaneous fission in spite of their high atomic mass.{{cite journal |last1=Ćwiok |first1=S. |last2=Heenen |first2=P.-H. |last3=Nazarewicz |first3=W. |year=2005 |title=Shape coexistence and triaxiality in the superheavy nuclei |url=http://www.phys.utk.edu/witek/fission/utk/Papers/natureSHE.pdf |journal=Nature |volume=433 |issue=7027 |pages=705–709 |bibcode=2005Natur.433..705C |doi=10.1038/nature03336 |pmid=15716943 |s2cid=4368001 |url-status=dead |archive-url=https://web.archive.org/web/20100623081932/http://www.phys.utk.edu/witek/fission/utk/Papers/natureSHE.pdf |archive-date=23 June 2010 }} It was thought that if such elements exist and are sufficiently long-lived, there may be several novel applications as a consequence of their nuclear and chemical properties. These include use in particle accelerators as neutron sources, in nuclear weapons as a consequence of their predicted low critical masses and high number of neutrons emitted per fission,{{cite book |last1=Gsponer |first1=A. |last2=Hurni |first2=J.-P. |year=2009 |title=Fourth Generation Nuclear Weapons: The physical principles of thermonuclear explosives, inertial confinement fusion, and the quest for fourth generation nuclear weapons |edition=3rd printing of the 7th |pages=110–115 |url=https://cryptome.org/2014/06/wmd-4th-gen-quest.pdf}} and as nuclear fuel to power space missions.{{cite news |last=Courtland |first=R. |title=Weight scale for atoms could map 'island of stability' |date=2010 |access-date=4 July 2019 |publisher=NewScientist |url=https://www.newscientist.com/article/dn18510-weight-scale-for-atoms-could-map-island-of-stability/}} These speculations led many researchers to conduct searches for superheavy elements in the 1960s and 1970s, both in nature and through nucleosynthesis in particle accelerators.

During the 1970s, many searches for long-lived superheavy nuclei were conducted. Experiments aimed at synthesizing elements ranging in atomic number from 110 to 127 were conducted at laboratories around the world.{{harvnb|Lodhi|1978|p=35}}{{harvnb|Emsley|2011|p=588}} These elements were sought in fusion-evaporation reactions, in which a heavy target made of one nuclide is irradiated by accelerated ions of another in a cyclotron, and new nuclides are produced after these nuclei fuse and the resulting excited system releases energy by evaporating several particles (usually protons, neutrons, or alpha particles). These reactions are divided into "cold" and "hot" fusion, which respectively create systems with lower and higher excitation energies; this affects the yield of the reaction.{{cite journal |last=Khuyagbaatar |first=J. |date=2017 |title=The cross sections of fusion-evaporation reactions: the most promising route to superheavy elements beyond Z = 118 |journal=EPJ Web of Conferences |volume=163 |pages=00030-1–00030-5 |doi=10.1051/epjconf/201716300030 |bibcode=2017EPJWC.16300030J |url=https://www.researchgate.net/publication/321229825|doi-access=free }} For example, the reaction between ²⁴⁸Cm and ⁴⁰Ar was expected to yield isotopes of element 114, and that between ²³²Th and ⁸⁴Kr was expected to yield isotopes of element 126.{{harvnb|Hoffman|2000|p=404}} None of these attempts were successful,{{harvnb|Emsley|2011|p=588}} indicating that such experiments may have been insufficiently sensitive if reaction cross sections were low—resulting in lower yields—or that any nuclei reachable via such fusion-evaporation reactions might be too short-lived for detection.{{efn|name=microsec}} Subsequent successful experiments reveal that half-lives and cross sections indeed decrease with increasing atomic number, resulting in the synthesis of only a few short-lived atoms of the heaviest elements in each experiment;{{cite web |url=https://cyclotron.tamu.edu/she2015/assets/pdfs/presentations/Karpov_SHE_2015_TAMU.pdf |title=Superheavy Nuclei: Which regions of nuclear map are accessible in the nearest studies? |last=Karpov |first=A. |last2=Zagrebaev |first2=V. |last3=Greiner |first3=W. |date=2015 |pages=1–16 |work=SHE-2015 |access-date=30 October 2018}} {{As of|2022|lc=y}}, the highest reported cross section for a superheavy nuclide near the island of stability is for ²⁸⁸Mc in the reaction between ²⁴³Am and ⁴⁸Ca.

Similar searches in nature were also unsuccessful, suggesting that if superheavy elements do exist in nature, their abundance is less than 10⁻¹⁴ moles of superheavy elements per mole of ore.{{harvnb|Hoffman|2000|p=403}} Despite these unsuccessful attempts to observe long-lived superheavy nuclei, new superheavy elements were synthesized every few years in laboratories through light-ion bombardment and cold fusion{{efn|This is a distinct concept from hypothetical fusion near room temperature (cold fusion); it instead refers to fusion reactions with lower excitation energy.}} reactions; rutherfordium, the first transactinide, was discovered in 1969, and copernicium, eight protons closer to the island of stability predicted at Z = 114, was reached by 1996. Even though the half-lives of these nuclei are very short (on the order of seconds),{{NUBASE2020 |ref |page=030001-174–030001-180}} the very existence of elements heavier than rutherfordium is indicative of stabilizing effects thought to be caused by closed shells; a model not considering such effects would forbid the existence of these elements due to rapid spontaneous fission.{{cite journal |last=Möller |first=P. |date=2016 |title=The limits of the nuclear chart set by fission and alpha decay |journal=EPJ Web of Conferences |volume=131 |pages=03002-1–03002-8 |url=http://inspirehep.net/record/1502715/files/epjconf-NS160-03002.pdf |doi=10.1051/epjconf/201613103002 |bibcode=2016EPJWC.13103002M|doi-access=free }}

Flerovium, with the expected magic 114 protons, was first synthesized in 1998 at the Joint Institute for Nuclear Research in Dubna, Russia, by a group of physicists led by Yuri Oganessian. A single atom of element 114 was detected, with a lifetime of 30.4 seconds, and its decay products had half-lives measurable in minutes.{{cite journal |last1=Oganessian |first1=Yu. Ts. |last2=Utyonkov |first2=V. K. |last3=Lobanov |first3=Yu. V. |display-authors=etal |date=1999 |title=Synthesis of Superheavy Nuclei in the ⁴⁸Ca + ²⁴⁴Pu Reaction |url=http://flerovlab.jinr.ru/linkc/flnr_presentations/articles/synthesis_of_Element_114_1999.pdf |journal=Physical Review Letters |volume=83 |issue=16 |page=3154 |bibcode=1999PhRvL..83.3154O |doi=10.1103/PhysRevLett.83.3154 |access-date=31 December 2018 |archive-date=30 July 2020 |archive-url=https://web.archive.org/web/20200730232521/http://flerovlab.jinr.ru/linkc/flnr_presentations/articles/synthesis_of_Element_114_1999.pdf |url-status=dead }} Because the produced nuclei underwent alpha decay rather than fission, and the half-lives were several orders of magnitude longer than those previously predicted{{efn|Oganessian stated that element 114 would have a half-life on the order of 10⁻¹⁹ s in the absence of stabilizing effects in the vicinity of the theorized island.{{cite web |last=Chapman |first=K. |date=2016 |title=What it takes to make a new element |url=https://www.chemistryworld.com/what-it-takes-to-make-a-new-element/1017677.article |publisher=Chemistry World |access-date=16 January 2020}}}} or observed for superheavy elements, this event was seen as a "textbook example" of a decay chain characteristic of the island of stability, providing strong evidence for the existence of the island of stability in this region.{{harvnb|Hoffman|2000|p=426}} Even though the original 1998 chain was not observed again, and its assignment remains uncertain,{{cite journal |last1=Hofmann |first1=S. |last2=Heinz |first2=S. |last3=Mann |first3=R. |last4=Maurer |first4=J. |last5=Münzenberg |first5=G. |last6=Antalic |first6=S. |last7=Barth |first7=W. |last8=Burkhard |first8=H. G. |last9=Dahl |first9=L. |last10=Eberhardt |first10=K. |last11=Grzywacz |first11=R. |last12=Hamilton |first12=J. H. |last13=Henderson |first13=R. A. |last14=Kenneally |first14=J. M. |last15=Kindler |first15=B. |display-authors=3 |date=2016 |title=Review of even element super-heavy nuclei and search for element 120 |url=https://www.researchgate.net/publication/304459935 |journal=The European Physical Journal A |volume=2016 |issue=52 |pages=180-15–180-17 |bibcode=2016EPJA...52..180H |doi=10.1140/epja/i2016-16180-4 |first16=I. |last16=Kojouharov |first17=R. |last17=Lang |first18=B. |last18=Lommel |first19=K. |last19=Miernik |first20=D. |last20=Miller |first21=K. J. |last21=Moody |first22=K. |last22=Morita |first23=K. |last23=Nishio |first24=A. G. |last24=Popeko |first25=J. B. |last25=Roberto |first26=J. |last26=Runke |first27=K. P. |last27=Rykaczewski |first28=S. |last28=Saro |first29=C. |last29=Scheidenberger |first30=H. J. |last30=Schött |first31=D. A. |last31=Shaughnessy |first32=M. A. |last32=Stoyer |first33=P. |last33=Thörle-Popiesch |first34=K. |last34=Tinschert |first35=N. |last35=Trautmann |first36=J. |last36=Uusitalo |first37=A. V. |last37=Yeremin |s2cid=124362890}} further successful experiments in the next two decades led to the discovery of all elements up to oganesson, whose half-lives were found to exceed initially predicted values; these decay properties further support the presence of the island of stability.{{cite journal |last1=Oganessian |first1=Yu. Ts. |last2=Rykaczewski |first2=K. |title=A beachhead on the island of stability |date=2015 |journal=Physics Today |volume=68 |issue=8 |pages=32–38 |doi=10.1063/PT.3.2880 |url=https://www.researchgate.net/publication/282806685 |bibcode=2015PhT....68h..32O|osti=1337838 |s2cid=119531411 |doi-access=free }}{{cite journal |last=Oganessian |first=Yu. Ts. |title=Heaviest nuclei from ⁴⁸Ca-induced reactions |date=2007 |journal=Journal of Physics G: Nuclear and Particle Physics |volume=34 |issue=4 |pages=R233 |doi=10.1088/0954-3899/34/4/R01 |url=https://www.nucleonica.com/wiki/images/4/41/Oganessian.pdf |bibcode=2007JPhG...34R.165O}}{{cite journal|last1=Oganessian |first1=Yu. Ts.|last2=Abdullin |first2=F. Sh.|last3=Bailey |first3=P. D. |last4=Benker |first4=D. E.|last5=Bennett |first5=M. E.|last6=Dmitriev |first6=S. N.|last7=Ezold |first7=J. G.|last8=Hamilton |first8=J. H.|last9=Henderson |first9=R. A. | first10=M. G. |last10=Itkis | first11=Yuri V. |last11=Lobanov | first12=A. N. |last12=Mezentsev | first13=K. J. |last13=Moody | first14=S. L. |last14=Nelson | first15=A. N. |last15=Polyakov | first16=C. E. |last16=Porter | first17=A. V. |last17=Ramayya | first18=F. D. |last18=Riley | first19=J. B.|last19=Roberto | first20=M. A. |last20=Ryabinin | first21=K. P. |last21=Rykaczewski | first22=R. N. |last22=Sagaidak | first23=D. A. |last23=Shaughnessy | first24=I. V. |last24=Shirokovsky | first25=M. A. |last25=Stoyer | first26=V. G. |last26=Subbotin | first27=R. |last27=Sudowe | first28=A. M. |last28=Sukhov | first29=Yu. S. |last29=Tsyganov | first30=Vladimir K. |last30=Utyonkov | first31=A. A. |last31=Voinov | first32=G. K. |last32=Vostokin | first33=P. A. |last33=Wilk|title=Synthesis of a New Element with Atomic Number Z = 117 |year=2010 |journal=Physical Review Letters |volume=104 |issue=14 |pages=142502-1–142502-4 |doi=10.1103/PhysRevLett.104.142502 |pmid=20481935 |bibcode=2010PhRvL.104n2502O |url=https://www.researchgate.net/publication/44610795 |display-authors=3 |doi-access=free }} However, a 2021 study on the decay chains of flerovium isotopes suggests that there is no strong stabilizing effect from Z = 114 in the region of known nuclei (N = 174),{{Cite journal |doi = 10.1103/PhysRevLett.126.032503 |issn=0031-9007|title = Spectroscopy along Flerovium Decay Chains: Discovery of ²⁸⁰Ds and an Excited State in ²⁸²Cn|journal = Physical Review Letters|volume = 126|pages = 032503-1–032503-7|year = 2021|last1 = Såmark-Roth|first1 = A.|last2 = Cox|first2 = D. M.|last3 = Rudolph|first3 = D.|last4 = Sarmento|first4 = L. G.|last5 = Carlsson|first5 = B. G.|last6 = Egido|first6 = J. L.|last7 = Golubev|first7 = P|last8 = Heery|first8 = J.|last9 = Yakushev|first9 = A.|last10 = Åberg|first10 = S.|last11 = Albers|first11 = H. M.|last12 = Albertsson|first12 = M.|last13 = Block|first13 = M.|last14 = Brand|first14 = H.|last15 = Calverley|first15 = T.|last16 = Cantemir|first16 = R.|last17 = Clark|first17 = R. M.|last18 = Düllmann|first18 = Ch. E.|last19 = Eberth|first19 = J.|last20 = Fahlander|first20 = C.|last21 = Forsberg|first21 = U.|last22 = Gates|first22 = J. M.|last23 = Giacoppo|first23 = F.|last24 = Götz|first24 = M.|last25 = Hertzberg|first25 = R.-D.|last26 = Hrabar|first26 = Y.|last27 = Jäger|first27 = E.|last28 = Judson|first28 = D.|last29 = Khuyagbaatar|first29 = J.|last30 = Kindler|first30 = B.|issue = 3|pmid = 33543956|bibcode = 2021PhRvL.126c2503S|display-authors = 3|doi-access = free|hdl = 10486/705608|hdl-access = free}} and that extra stability would be predominantly a consequence of the neutron shell closure. Although known nuclei still fall several neutrons short of N = 184 where maximum stability is expected (the most neutron-rich confirmed nuclei, ²⁹³Lv and ²⁹⁴Ts, only reach N = 177), and the exact location of the center of the island remains unknown,{{cite web |url=http://newscenter.lbl.gov/2009/09/24/114-confirmed/ |title=Superheavy Element 114 Confirmed: A Stepping Stone to the Island of Stability |date=2009 |access-date=23 October 2019 |publisher=Berkeley Lab}} the trend of increasing stability closer to N = 184 has been demonstrated. For example, the isotope ²⁸⁵Cn, with eight more neutrons than ²⁷⁷Cn, has a half-life almost five orders of magnitude longer. This trend is expected to continue into unknown heavier isotopes in the vicinity of the shell closure.

File:Even Z alpha decay chains.svgThough nuclei within the island of stability around N = 184 are predicted to be spherical, studies from the early 1990s—beginning with Polish physicists Zygmunt Patyk and Adam Sobiczewski in 1991{{Cite journal|last1=Patyk|first1=Z.|last2=Sobiczewski|first2=A.|date=1991|title=Ground-state properties of the heaviest nuclei analyzed in a multidimensional deformation space|journal=Nuclear Physics A|language=en|volume=533|issue=1|page=150|bibcode=1991NuPhA.533..132P|doi=10.1016/0375-9474(91)90823-O}}—suggest that some superheavy elements do not have perfectly spherical nuclei.{{cite journal |title=Structure of Odd-N Superheavy Elements |journal=Physical Review Letters |volume=83 |issue=6 |pages=1108–1111 |year=1999 |doi=10.1103/PhysRevLett.83.1108 |last1=Ćwiok |first1=S. |last2=Nazarewicz |first2=W. |last3=Heenen |first3=P. H. |bibcode=1999PhRvL..83.1108C }}{{cite journal |last1=Zagrebaev |first1=V. I. |last2=Aritomo |first2=Y. |last3=Itkis |first3=M. G. |last4=Oganessian |first4=Yu. Ts. |last5=Ohta |first5=N. |display-authors=3 |title=Synthesis of superheavy nuclei: How accurately can we describe it and calculate the cross sections? |date=2001 |journal=Physical Review C |volume=65 |issue=1 |pages=014607-1–014607-14 |doi=10.1103/PhysRevC.65.014607 |bibcode=2001PhRvC..65a4607Z |url=http://nrv.jinr.ru/pdf_file/zaioo.pdf}} A change in the shape of the nucleus changes the position of neutrons and protons in the shell. Research indicates that large nuclei farther from spherical magic numbers are deformed, causing magic numbers to shift or new magic numbers to appear. Current theoretical investigation indicates that in the region Z = 106–108 and N ≈ 160–164, nuclei may be more resistant to fission as a consequence of shell effects for deformed nuclei; thus, such superheavy nuclei would only undergo alpha decay. Hassium-270 is now believed to be a doubly magic deformed nucleus, with deformed magic numbers Z = 108 and N = 162.{{Cite journal |first1=J. |last1=Dvořák |first2 =W. |last2= Brüchle |first3= M. |last3= Chelnokov |first4= R. |last4= Dressler |first5= Ch. E. |last5= Düllmann |first6= K. |last6= Eberhardt |first7= V. |last7= Gorshkov |first8= E. |last8= Jäger |first9= R. |last9= Krücken |first10= A. |last10= Kuznetsov |first11= Y. |last11= Nagame |first12= F. |last12= Nebel |first13= Z. |last13= Novackova |first14= Z. |last14= Qin |first15= M. |last15= Schädel |first16= B. |last16= Schausten |first17= E. |last17= Schimpf |first18= A. |last18= Semchenkov |first19= P. |last19= Thörle |first20= A. |last20= Türler |first21= M. |last21= Wegrzecki |first22= B. |last22= Wierczinski |first23= A. |last23= Yakushev |first24= A. |last24= Yeremin

|display-authors=3 |year=2006 |title=Doubly Magic Nucleus {{su|p=270|b=108}}Hs{{su|b=162}} |journal=Physical Review Letters |volume=97 |issue=24 |pages=242501-1–242501-4 |bibcode=2006PhRvL..97x2501D |doi=10.1103/PhysRevLett.97.242501 |pmid=17280272|url=https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A16351 }} It has a half-life of 9 seconds.{{NUBASE2020 |ref |page=030001-174–030001-180}} This is consistent with models that take into account the deformed nature of nuclei intermediate between the actinides and island of stability near N = 184, in which a stability "peninsula" emerges at deformed magic numbers Z = 108 and N = 162.{{cite journal |last1=Möller |first1=P. |last2=Nix |first2=J. R. |title=Stability and Production of Superheavy Nuclei |date=1998 |journal=AIP Conference Proceedings |volume=425 |issue=1 |pages=75 |doi=10.1063/1.55136 |arxiv=nucl-th/9709016|bibcode=1998AIPC..425...75M |s2cid=119087649 }}{{cite journal |last1=Meng |first1=X. |last2=Lu |first2=B.-N. |last3=Zhou |first3=S.-G. |title=Ground state properties and potential energy surfaces of ²⁷⁰Hs from multidimensionally constrained relativistic mean field model |date=2020 |journal=Science China Physics, Mechanics & Astronomy |volume=63 |issue=1 |pages=212011-1–212011-9 |doi=10.1007/s11433-019-9422-1 |arxiv=1910.10552|bibcode=2020SCPMA..6312011M |s2cid=204838163 }} Determination of the decay properties of neighboring hassium and seaborgium isotopes near N = 162 provides further strong evidence for this region of relative stability in deformed nuclei. This also strongly suggests that the island of stability (for spherical nuclei) is not completely isolated from the region of stable nuclei, but rather that both regions are instead linked through an isthmus of relatively stable deformed nuclei.{{cite book |editor-last=Schädel |editor-first=M. |editor-last2=Shaughnessy |editor-first2=D. |title=The Chemistry of Superheavy Elements |year=2014 |edition=2nd |publisher=Springer |page=3 |chapter=Synthesis of Superheavy Elements |last=Moody |first=K. J. |isbn=978-3-642-37466-1}}

File:Superheavy decay modes predicted.png (β) or electron capture (EC) branches may appear closest to the center of the island around ²⁹¹Cn and ²⁹³Cn.]]

The half-lives of nuclei in the island of stability itself are unknown since none of the nuclides that would be "on the island" have been observed. Many physicists believe that the half-lives of these nuclei are relatively short, on the order of minutes or days. Some theoretical calculations indicate that their half-lives may be long, on the order of 100 years, or possibly as long as 10⁹ years.

The shell closure at N = 184 is predicted to result in longer partial half-lives for alpha decay and spontaneous fission. It is believed that the shell closure will result in higher fission barriers for nuclei around ²⁹⁸Fl, strongly hindering fission and perhaps resulting in fission half-lives 30 orders of magnitude greater than those of nuclei unaffected by the shell closure.{{cite conference|last=Koura|first=H.|date=2011|title=Decay modes and a limit of existence of nuclei in the superheavy mass region|url=http://tan11.jinr.ru/pdf/10_Sep/S_2/05_Koura.pdf|conference=4th International Conference on the Chemistry and Physics of the Transactinide Elements|access-date=18 November 2018}} For example, the neutron-deficient isotope ²⁸⁴Fl (with N = 170) undergoes fission with a half-life of 2.5 milliseconds, and is thought to be one of the most neutron-deficient nuclides with increased stability in the vicinity of the N = 184 shell closure.{{cite journal |last1=Utyonkov |first1=V. K. |last2=Brewer |first2=N. T. |first3=Yu. Ts. |last3=Oganessian |first4=K. P. |last4=Rykaczewski |first5=F. Sh. |last5=Abdullin |first6=S. N. |last6=Dimitriev |first7=R. K. |last7=Grzywacz |first8=M. G. |last8=Itkis |first9=K. |last9=Miernik |first10=A. N. |last10=Polyakov |first11=J. B. |last11=Roberto |first12=R. N. |last12=Sagaidak |first13=I. V. |last13=Shirokovsky |first14=M. V. |last14=Shumeiko |first15=Yu. S. |last15=Tsyganov |first16=A. A. |last16=Voinov |first17=V. G. |last17=Subbotin |first18=A. M. |last18=Sukhov |first19=A. V. |last19=Karpov |first20=A. G. |last20=Popeko |first21=A. V. |last21=Sabel'nikov |first22=A. I. |last22=Svirikhin |first23=G. K. |last23=Vostokin |first24=J. H. |last24=Hamilton |first25=N. D. |last25=Kovrinzhykh |first26=L. |last26=Schlattauer |first27=M. A. |last27=Stoyer |first28=Z. |last28=Gan |first29=W. X. |last29=Huang |first30=L. |last30=Ma |display-authors=3 |date=2018 |title=Neutron-deficient superheavy nuclei obtained in the ²⁴⁰Pu + ⁴⁸Ca reaction |journal=Physical Review C |volume=97 |issue=1 |pages=014320-1–014320-10 |doi=10.1103/PhysRevC.97.014320|bibcode=2018PhRvC..97a4320U |url=https://www.researchgate.net/publication/322812255|doi-access=free }} Beyond this point, some undiscovered isotopes are predicted to undergo fission with still shorter half-lives, limiting the existence{{efn|The International Union of Pure and Applied Chemistry (IUPAC) defines the limit of nuclear existence at a half-life of 10⁻¹⁴ seconds; this is approximately the time required for nucleons to arrange themselves into nuclear shells and thus form a nuclide.{{harvnb|Emsley|2011|p=590}}}} and possible observation{{efn|name=microsec|While such nuclei may be synthesized and a series of decay signals may be registered, decays faster than one microsecond may pile up with subsequent signals and thus be indistinguishable, especially when multiple uncharacterized nuclei may be formed and emit a series of similar alpha particles.{{cite journal |title=New short-lived isotope ²²³Np and the absence of the Z = 92 subshell closure near N = 126

|first1=M. D. |last1=Sun |first2=Z. |last2=Liu |first3=T. H. |last3=Huang |display-authors=et al. |journal=Physics Letters B |volume=771 |date=2017 |pages=303–308 |doi=10.1016/j.physletb.2017.03.074 |url=https://www.researchgate.net/publication/317142406|bibcode=2017PhLB..771..303S |doi-access=free }} The main difficulty is thus attributing the decays to the correct parent nucleus, as a superheavy atom that decays before reaching the detector will not be registered at all.}} of superheavy nuclei far from the island of stability (namely for N < 170 as well as for Z > 120 and N > 184). These nuclei may undergo alpha decay or spontaneous fission in microseconds or less, with some fission half-lives estimated on the order of 10⁻²⁰ seconds in the absence of fission barriers. In contrast, ²⁹⁸Fl (predicted to lie within the region of maximum shell effects) may have a much longer spontaneous fission half-life, possibly on the order of 10¹⁹ years.

In the center of the island, there may be competition between alpha decay and spontaneous fission, though the exact ratio is model-dependent. The alpha decay half-lives of 1700 nuclei with 100 ≤ Z ≤ 130 have been calculated in a quantum tunneling model with both experimental and theoretical alpha decay Q-values, and are in agreement with observed half-lives for some of the heaviest isotopes.{{Cite journal |last1=Samanta |first1=C. |last2=Chowdhury |first2=P. R. |last3=Basu |first3=D. N. |year=2007 |title=Predictions of alpha decay half lives of heavy and superheavy elements |journal=Nuclear Physics A |volume=789 |issue= 1–4|pages=142–154 |arxiv=nucl-th/0703086 |bibcode=2007NuPhA.789..142S |doi=10.1016/j.nuclphysa.2007.04.001|citeseerx=10.1.1.264.8177 |s2cid=7496348 }}{{Cite journal |last1=Chowdhury |first1=P. R. |last2=Samanta |first2=C. |last3=Basu |first3=D. N. |year=2008 |title=Search for long lived heaviest nuclei beyond the valley of stability |journal=Physical Review C |volume=77 |issue=4 |pages=044603-1–044603-14 |arxiv=0802.3837 |bibcode=2008PhRvC..77d4603C |doi=10.1103/PhysRevC.77.044603|s2cid=119207807 }}{{Cite journal |last1=Chowdhury |first1=P. R. |last2=Samanta |first2=C. |last3=Basu |first3=D. N. |year=2008 |title=Nuclear half-lives for α-radioactivity of elements with 100 ≤ Z ≤ 130 |journal=Atomic Data and Nuclear Data Tables |volume=94 |issue=6 |pages=781–806 |arxiv=0802.4161 |bibcode=2008ADNDT..94..781C |doi=10.1016/j.adt.2008.01.003|s2cid=96718440 }}{{Cite journal |last1=Chowdhury |first1=P. R. |last2=Samanta |first2=C. |last3=Basu |first3=D. N. |year=2006 |title=α decay half-lives of new superheavy elements |journal=Physical Review C |volume=73 |issue= 1|pages=014612-1–014612-7 |arxiv=nucl-th/0507054 |bibcode=2006PhRvC..73a4612C |doi=10.1103/PhysRevC.73.014612|s2cid=118739116 }}{{Cite journal |last1=Chowdhury |first1=P. R. |last2=Basu |first2=D. N. |last3=Samanta |first3=C. |date=2007 |title=α decay chains from element 113 |journal=Physical Review C |volume=75 |issue=4 |pages=047306-1–047306-3 |arxiv=0704.3927 |bibcode=2007PhRvC..75d7306C |doi=10.1103/PhysRevC.75.047306|s2cid=118496739 }}{{Cite journal |last1=Samanta |first1=C. |last2=Basu |first2=D. N. |last3=Chowdhury |first3=P. R. |year=2007 |title=Quantum tunneling in ²⁷⁷112 and its alpha-decay chain |journal=Journal of the Physical Society of Japan |volume=76 |issue=12 |pages=124201-1–124201-4 |arxiv=0708.4355 |bibcode=2007JPSJ...76l4201S |doi=10.1143/JPSJ.76.124201|s2cid=14210523 }}

The longest-lived nuclides are also predicted to lie on the beta-stability line, for beta decay is predicted to compete with the other decay modes near the predicted center of the island, especially for isotopes of elements 111–115. Unlike other decay modes predicted for these nuclides, beta decay does not change the mass number. Instead, a neutron is converted into a proton or vice versa, producing an adjacent isobar closer to the center of stability (the isobar with the lowest mass excess). For example, significant beta decay branches may exist in nuclides such as ²⁹¹Fl and ²⁹¹Nh; these nuclides have only a few more neutrons than known nuclides, and might decay via a "narrow pathway" towards the center of the island of stability. The possible role of beta decay is highly uncertain, as some isotopes of these elements (such as ²⁹⁰Fl and ²⁹³Mc) are predicted to have shorter partial half-lives for alpha decay. Beta decay would reduce competition and would result in alpha decay remaining the dominant decay channel, unless additional stability towards alpha decay exists in superdeformed isomers of these nuclides.{{cite journal |last=Sarriguren |first=P. |title=Microscopic calculations of weak decays in superheavy nuclei |date=2019 |journal=Physical Review C |volume=100 |issue=1 |pages=014309-1–014309-12 |doi=10.1103/PhysRevC.100.014309 |arxiv=1907.06877|bibcode=2019PhRvC.100a4309S |s2cid=196831777 }}

File:Superheavy decay modes predicted (KTUY).svg, predicts the center of the island of stability around ²⁹⁴Ds; it would be the longest-lived of several relatively long-lived nuclides primarily undergoing alpha decay (circled). This is the region where the beta-stability line crosses the region stabilized by the shell closure at N = 184. To the left and right, half-lives decrease as fission becomes the dominant decay mode, consistent with other models.]]

Considering all decay modes, various models indicate a shift of the center of the island (i.e., the longest-living nuclide) from ²⁹⁸Fl to a lower atomic number, and competition between alpha decay and spontaneous fission in these nuclides;{{cite journal |last1=Nilsson |first1=S. G. |last2=Tsang |first2=C. F. |last3=Sobiczewski |first3=A. |display-authors=etal |year=1969 |title=On the nuclear structure and stability of heavy and superheavy elements |journal=Nuclear Physics A |volume=131 |issue=1 |pages=53–55 |bibcode = 1969NuPhA.131....1N |doi=10.1016/0375-9474(69)90809-4|url=http://www.escholarship.org/uc/item/0d8319f2 |type=Submitted manuscript }} these include 100-year half-lives for ²⁹¹Cn and ²⁹³Cn,{{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|issn=1062-8738|url=http://nrv.jinr.ru/karpov/publications/Palenzuela12_BRAS.pdf|doi=10.3103/S1062873812110172|bibcode=2012BRASP..76.1165P|s2cid=120690838}} a 1000-year half-life for ²⁹⁶Cn, a 300-year half-life for ²⁹⁴Ds, and a 3500-year half-life for ²⁹³Ds,{{cite journal |author=Chowdhury |first=P. Roy |author2=Samanta |first2=C. |author3=Basu |first3=D. N. |name-list-style=amp |year=2008 |title=Search for long lived heaviest nuclei beyond the valley of stability |journal=Physical Review C |volume=77 |issue=4 |page=044603 |arxiv=0802.3837 |bibcode=2008PhRvC..77d4603C |doi=10.1103/PhysRevC.77.044603 |s2cid=119207807}}{{cite journal |author=Chowdhury |first=P. Roy |author2=Samanta |first2=C. |author3=Basu |first3=D. N. |name-list-style=amp |year=2008 |title=Nuclear half-lives for α -radioactivity of elements with 100 ≤ Z ≤ 130 |journal=Atomic Data and Nuclear Data Tables |volume=94 |issue=6 |pages=781–806 |arxiv=0802.4161 |bibcode=2008ADNDT..94..781C |doi=10.1016/j.adt.2008.01.003 |s2cid=96718440}} with ²⁹⁴Ds and ²⁹⁶Cn exactly at the N = 184 shell closure. It has also been posited that this region of enhanced stability for elements with 112 ≤ Z ≤ 118 may instead be a consequence of nuclear deformation, and that the true center of the island of stability for spherical superheavy nuclei lies around ³⁰⁶Ubb (Z = 122, N = 184).{{cite conference |last1=Kratz |first1=J. V. |date=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 |pages=30–37 |conference=4th International Conference on the Chemistry and Physics of the Transactinide Elements |access-date=27 August 2013}} This model defines the island of stability as the region with the greatest resistance to fission rather than the longest total half-lives; the nuclide ³⁰⁶Ubb is still predicted to have a short half-life with respect to alpha decay. The island of stability for spherical nuclei may also be a "coral reef" (i.e., a broad region of increased stability without a clear "peak") around N = 184 and 114 ≤ Z ≤ 120, with half-lives rapidly decreasing at higher atomic number, due to combined effects from proton and neutron shell closures.{{cite journal |doi=10.1103/PhysRevC.104.064303 |last1=Malov |first1=L. A. |last2=Adamian |first2=G. G. |last3=Antonenko |first3=N. V. |last4=Lenske |first4=H. |title=Landscape of the island of stability with self-consistent mean-field potentials |date=2021 |journal=Physical Review C |volume=104 |issue=6 |pages=064303-1–064303-12|bibcode=2021PhRvC.104f4303M |s2cid=244927833 }}

Another potentially significant decay mode for the heaviest superheavy elements was proposed to be cluster decay by Romanian physicists Dorin N. Poenaru and Radu A. Gherghescu and German physicist Walter Greiner. Its branching ratio relative to alpha decay is expected to increase with atomic number such that it may compete with alpha decay around Z = 120, and perhaps become the dominant decay mode for heavier nuclides around Z = 124. As such, it is expected to play a larger role beyond the center of the island of stability (though still influenced by shell effects), unless the center of the island lies at a higher atomic number than predicted.{{Cite journal |last1=Poenaru |first1=D. N. |last2=Gherghescu |first2=R. A. |last3=Greiner |first3=W. |year=2011 |title=Heavy-Particle Radioactivity of Superheavy Nuclei |journal=Physical Review Letters |volume=107 |issue=6 |pages=062503-1–062503-4 |arxiv=1106.3271 |bibcode=2011PhRvL.107f2503P |doi=10.1103/PhysRevLett.107.062503 |pmid=21902317|s2cid=38906110 }}

{{see also|Extinct isotopes of superheavy elements}}

Even though half-lives of hundreds or thousands of years would be relatively long for superheavy elements, they are far too short for any such nuclides to exist primordially on Earth. Additionally, instability of nuclei intermediate between primordial actinides (²³²Th, ²³⁵U, and ²³⁸U) and the island of stability may inhibit production of nuclei within the island in r-process nucleosynthesis. Various models suggest that spontaneous fission will be the dominant decay mode of nuclei with A > 280, and that neutron-induced or beta-delayed fission—respectively neutron capture and beta decay immediately followed by fission—will become the primary reaction channels. As a result, beta decay towards the island of stability may only occur within a very narrow path or may be entirely blocked by fission, thus precluding the synthesis of nuclides within the island.{{cite journal |last1=Petermann |first1=I. |last2=Langanke |first2=K. |last3=Martínez-Pinedo |first3=G. |last4=Panov |first4=I. V. |last5=Reinhard |first5=P. G. |last6=Thielemann |first6=F. K. |display-authors=3 |date=2012 |title=Have superheavy elements been produced in nature? |url=https://www.researchgate.net/publication/229156774 |journal=European Physical Journal A |language=en |volume=48 |issue=122 |page=122 |arxiv=1207.3432 |bibcode=2012EPJA...48..122P |doi=10.1140/epja/i2012-12122-6 |s2cid=119264543}} The non-observation of superheavy nuclides such as ²⁹²Hs and ²⁹⁸Fl in nature is thought to be a consequence of a low yield in the r-process resulting from this mechanism, as well as half-lives too short to allow measurable quantities to persist in nature.{{cite journal| last1=Ludwig |first1=P. |last2=Faestermann |first2=T. |last3=Korschinek |first3=G. |last4=Rugel |first4=G. |last5=Dillmann |first5=I. |last6=Fimiani |first6=L. |last7=Bishop |first7=S. |last8=Kumar |first8=P. |display-authors=3 |title=Search for superheavy elements with 292 ≤ A ≤ 310 in nature with accelerator mass spectrometry |date=2012 |journal=Physical Review C |volume=85 |issue=2 |pages=024315-1–024315-8 |doi=10.1103/PhysRevC.85.024315 |url=https://www.nucastro.ph.tum.de/fileadmin/tuphena/www/pubs/e024315.pdf |archive-url=https://web.archive.org/web/20181228223425/https://www.nucastro.ph.tum.de/fileadmin/tuphena/www/pubs/e024315.pdf |archive-date=28 December 2018 |url-status=live}}{{efn|The observation of long-lived isotopes of roentgenium (with A {{=}} 261, 265) and unbibium (A {{=}} 292) in nature has been claimed by Israeli physicist Amnon Marinov et al.,{{cite journal |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 |display-authors=3 |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 Publishing Company |doi=10.1142/S021830130901280X |url=http://www.phys.huji.ac.il/~marinov/publications/Au_paper_IJMPE_73.pdf |access-date=12 February 2012 |arxiv=nucl-ex/0702051 |bibcode=2009IJMPE..18..621M |s2cid=119103410 |archive-url=https://web.archive.org/web/20140714210340/http://www.phys.huji.ac.il/~marinov/publications/Au_paper_IJMPE_73.pdf |archive-date=14 July 2014 |url-status=dead }}{{cite journal |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. |display-authors=3 |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|year=2010 |arxiv=0804.3869 |bibcode = 2010IJMPE..19..131M |doi = 10.1142/S0218301310014662 |volume=19 |issue=1 |pages=131–140 |s2cid=117956340 }} though evaluations of the technique used and subsequent unsuccessful searches cast considerable doubt on these results.}} Various studies utilizing accelerator mass spectroscopy and crystal scintillators have reported upper limits of the natural abundance of such long-lived superheavy nuclei on the order of {{val|e=-14}} relative to their stable homologs.{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Cappella |first3=F. |last4=Caracciolo |first4=V. |last5=Cerulli |first5=R. |last6=Danevich |first6=F. A. |last7=Incicchitti |first7=A. |last8=Kasperovych |first8=D. V.|last9=Kobychev |first9=V. V. |last10=Laubenstein |first10=M. |last11=Poda |first11=D. V. |last12=Polischuk |first12=O. G. |last13=Sokur |first13=N. V. |last14=Tretyak |first14=V. I. |display-authors=3 |title=Search for naturally occurring seaborgium with radiopure ¹¹⁶CdWO₄ crystal scintillators |date=2022 |journal=Physica Scripta |volume=97 |number=85302 |page=085302 |doi=10.1088/1402-4896/ac7a6d|bibcode=2022PhyS...97h5302B |s2cid=249902412 }}

Despite these obstacles to their synthesis, a 2013 study published by a group of Russian physicists led by Valeriy Zagrebaev proposes that the longest-lived copernicium isotopes may occur at an abundance of 10⁻¹² relative to lead, whereby they may be detectable in cosmic rays. Similarly, in a 2013 experiment, a group of Russian physicists led by Aleksandr Bagulya reported the possible observation of three cosmogenic superheavy nuclei in olivine crystals in meteorites. The atomic number of these nuclei was estimated to be between 105 and 130, with one nucleus likely constrained between 113 and 129, and their lifetimes were estimated to be at least 3,000 years. Although this observation has yet to be confirmed in independent studies, it strongly suggests the existence of the island of stability, and is consistent with theoretical calculations of half-lives of these nuclides.{{cite journal |last1=Bagulya |first1=A. V. |last2=Vladimirov |first2=M. S. |last3=Volkov |first3=A. E. |last4=Goncharova |first4=L. A. |last5=Gorbunov |first5=S. A. |last6=Kalinina |first6=G. V. |last7=Konovalova |first7=N. S. |last8=Okatyeva |first8=N. M. |last9=Pavolva |first9=T. A. |last10=Polukhina |first10=N. G. |last11=Starkov |first11=N. I. |last12=Soe |first12=T. N. |last13=Chernyavsky |first13=M. M. |last14=Shchedrina |first14=T. V. |display-authors=3 |title=Charge spectrum of superheavy nuclei of galactic cosmic rays obtained in the OLIMPIA experiment |journal=Bulletin of the Lebedev Physics Institute |date=2015 |volume=42 |issue=5 |pages=152–156 |doi=10.3103/S1068335615050073 |url=https://www.researchgate.net/publication/279166139|bibcode=2015BLPI...42..152B |s2cid=124044490 }}{{cite arXiv |first1=A. |last1= Alexandrov |first2= V. |last2= Alexeev |first3= A. |last3= Bagulya |first4= A. |last4= Dashkina |first5= M. |last5= Chernyavsky |first6= A. |last6= Gippius |first7= L. |last7= Goncharova |first8= S. |last8= Gorbunov |first9= V. |last9= Grachev |first10= G. |last10= Kalinina |first11= N. |last11= Konovalova |first12= N. |last12= Okateva |first13= T. |last13= Pavlova |first14= N. |last14= Polukhina |first15= R. |last15= Rymzhanov |first16= N. |last16= Starkov |first17= T. N. |last17= Soe |first18= T. |last18= Shchedrina |first19= A. |last19= Volkov |display-authors=3 |title=Natural superheavy nuclei in astrophysical data |date=2019 |eprint=1908.02931 |class=nucl-ex }}{{cite journal |title=Superheavy elements: Oganesson and beyond |date=2019 |last1=Giuliani |first1=S. A. |last2=Matheson |first2=Z. |last3=Nazarewicz |first3=W. |display-authors=et al. |journal=Reviews of Modern Physics |volume=91 |issue=1 |pages=24–27 |doi=10.1103/RevModPhys.91.011001 |osti=1513815 |doi-access=free }}

The decay of heavy, long-lived elements in the island of stability is a proposed explanation for the unusual presence of the short-lived radioactive isotopes observed in Przybylski's Star.{{Cite journal |author1=V. A. Dzuba |author2=V. V. Flambaum |author3=J. K. Webb |year=2017 |title=Isotope shift and search for metastable superheavy elements in astrophysical data |journal=Physical Review A |volume=95 |issue=6 |pages=062515 |arxiv=1703.04250 |bibcode=2017PhRvA..95f2515D |doi=10.1103/PhysRevA.95.062515 |s2cid=118956691}}

File:Island of Stability.svg = 178 and Z = 112]]

The manufacture of nuclei on the island of stability proves to be very difficult because the nuclei available as starting materials do not deliver the necessary sum of neutrons. Radioactive ion beams (such as ⁴⁴S) in combination with actinide targets (such as ²⁴⁸Cm) may allow the production of more neutron rich nuclei nearer to the center of the island of stability, though such beams are not currently available in the required intensities to conduct such experiments.{{cite conference |last=Popeko |first=A. G. |title=Perspectives of SHE research at Dubna |date=2016 |conference=NUSTAR Annual Meeting 2016 |location=Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany |pages=22–28 |url=https://indico.gsi.de/event/3548/session/23/contribution/45/material/slides/}} Several heavier isotopes such as ²⁵⁰Cm and ²⁵⁴Es may still be usable as targets, allowing the production of isotopes with one or two more neutrons than known isotopes,{{cite conference |last1=Zagrebaev |first1=V. |last2=Karpov |first2=A. |last3=Greiner |first3=W. |date=2013 |title=Future of superheavy element research: Which nuclei could be synthesized within the next few years? |publisher=IOP Science |book-title=Journal of Physics: Conference Series |volume=420 |pages=1–15 |arxiv=1207.5700 |doi=10.1088/1757-899X/468/1/012012 }} though the production of several milligrams of these rare isotopes to create a target is difficult.{{cite web |url=https://cyclotron.tamu.edu/she2015/assets/pdfs/presentations/Roberto_SHE_2015_TAMU.pdf |title=Actinide Targets for Super-Heavy Element Research |last=Roberto |first=J. B. |date=2015 |website=cyclotron.tamu.edu |publisher=Texas A & M University |pages=3–6 |access-date=30 October 2018}} It may also be possible to probe alternative reaction channels in the same ⁴⁸Ca-induced fusion-evaporation reactions that populate the most neutron-rich known isotopes, namely those at a lower excitation energy (resulting in fewer neutrons being emitted during de-excitation), or those involving evaporation of charged particles (pxn, evaporating a proton and several neutrons, or αxn, evaporating an alpha particle and several neutrons).{{cite conference |url=https://indico.jinr.ru/event/3622/contributions/20021/attachments/15292/25806/Yerevan2023.pdf |title=Interesting fusion reactions in superheavy region |first1=J. |last1=Hong |first2=G. G. |last2=Adamian |first3=N. V. |last3=Antonenko |first4=P. |last4=Jachimowicz |first5=M. |last5=Kowal |conference=IUPAP Conference "Heaviest nuclei and atoms" |publisher=Joint Institute for Nuclear Research |date=26 April 2023 |access-date=30 July 2023}} This may allow the synthesis of neutron-enriched isotopes of elements 111–117. Although the predicted cross sections are on the order of 1–900 fb, smaller than when only neutrons are evaporated (xn channels), it may still be possible to generate otherwise unreachable isotopes of superheavy elements in these reactions.{{cite journal |last1=Hong |first1=J. |last2=Adamian |first2=G. G. |last3=Antonenko |first3=N. V. |date=2017 |title=Ways to produce new superheavy isotopes with Z = 111–117 in charged particle evaporation channels |journal=Physics Letters B |volume=764 |pages=42–48 |doi=10.1016/j.physletb.2016.11.002 |bibcode=2017PhLB..764...42H|doi-access=free }}{{cite journal |last1=Siwek-Wilczyńska |first1=K. |last2=Cap |first2=T. |last3=Kowal |first3=P. |date=2019 |title=How to produce new superheavy nuclei? |arxiv=1812.09522 |doi=10.1103/PhysRevC.99.054603 |journal=Physical Review C |volume=99 |issue=5 |pages=054603-1–054603-5|s2cid=155404097 }} Some of these heavier isotopes (such as ²⁹¹Mc, ²⁹¹Fl, and ²⁹¹Nh) may also undergo electron capture (converting a proton into a neutron) in addition to alpha decay with relatively long half-lives, decaying to nuclei such as ²⁹¹Cn that are predicted to lie near the center of the island of stability. However, this remains largely hypothetical as no superheavy nuclei near the beta-stability line have yet been synthesized and predictions of their properties vary considerably across different models. In 2024, a team of researchers at the JINR observed one decay chain of the known isotope ²⁸⁹Mc as a product in the p2n channel of the reaction between ²⁴²Pu and ⁵⁰Ti, an experiment targeting neutron-deficient livermorium isotopes. This was the first successful report of a charged-particle exit channel in a hot fusion reaction between an actinide target and a projectile with Z ≥ 20.{{Cite web |url=https://indico.jinr.ru/event/4343/contributions/28663/attachments/20748/36083/U%20+%20Cr%20AYSS%202024.pptx |title=Synthesis and study of the decay properties of isotopes of superheavy element Lv in Reactions ²³⁸U + ⁵⁴Cr and ²⁴²Pu + ⁵⁰Ti |last=Ibadullayev |first=Dastan |date=2024 |website=jinr.ru |publisher=Joint Institute for Nuclear Research |access-date=2 November 2024 |quote=}}

The process of slow neutron capture used to produce nuclides as heavy as ²⁵⁷Fm is blocked by short-lived isotopes of fermium that undergo spontaneous fission (for example, ²⁵⁸Fm has a half-life of 370 μs); this is known as the "fermium gap" and prevents the synthesis of heavier elements in such a reaction. It might be possible to bypass this gap, as well as another predicted region of instability around A = 275 and Z = 104–108, in a series of controlled nuclear explosions with a higher neutron flux (about a thousand times greater than fluxes in existing reactors) that mimics the astrophysical r-process. First proposed in 1972 by Meldner, such a reaction might enable the production of macroscopic quantities of superheavy elements within the island of stability; the role of fission in intermediate superheavy nuclides is highly uncertain, and may strongly influence the yield of such a reaction.

File:Nuclear chart from KTUY model.svg

It may also be possible to generate isotopes in the island of stability such as ²⁹⁸Fl in multi-nucleon transfer reactions in low-energy collisions of actinide nuclei (such as ²³⁸U and ²⁴⁸Cm). This inverse quasifission (partial fusion followed by fission, with a shift away from mass equilibrium that results in more asymmetric products) mechanism{{cite journal |last=Sekizawa |first=K. |date=2019 |title=TDHF theory and its extensions for the multinucleon transfer reaction: A mini review |journal=Frontiers in Physics |volume=7 |number=20 |arxiv=1902.01616 |doi=10.3389/fphy.2019.00020 |bibcode=2019FrP.....7...20S |pages=1–6|s2cid=73729050 |doi-access=free }} may provide a path to the island of stability if shell effects around Z = 114 are sufficiently strong, though lighter elements such as nobelium and seaborgium (Z = 102–106) are predicted to have higher yields.{{cite journal |last1=Zagrebaev |first1=V. |last2=Greiner |first2=W. |year=2008 |title=Synthesis of superheavy nuclei: A search for new production reactions |journal=Physical Review C |volume=78 |issue=3 |pages=034610-1–034610-12 |arxiv=0807.2537 |bibcode=2008PhRvC..78c4610Z |doi=10.1103/PhysRevC.78.034610}} Preliminary studies of the ²³⁸U + ²³⁸U and ²³⁸U + ²⁴⁸Cm transfer reactions have failed to produce elements heavier than mendelevium (Z = 101), though the increased yield in the latter reaction suggests that the use of even heavier targets such as ²⁵⁴Es (if available) may enable production of superheavy elements.{{cite journal |last1=Schädel |first1=M. |title=Prospects of heavy and superheavy element production via inelastic nucleus-nucleus collisions – from {{sup|238}}U + {{sup|238}}U to {{sup|18}}O + {{sup|254}}Es |journal=EPJ Web of Conferences |date=2016 |volume=131 |pages=04001-1–04001-9 |doi=10.1051/epjconf/201613104001 |url=https://inspirehep.net/record/1502716/files/epjconf-NS160-04001.pdf|doi-access=free }} This result is supported by a later calculation suggesting that the yield of superheavy nuclides (with Z ≤ 109) will likely be higher in transfer reactions using heavier targets.{{cite journal |last1=Zhu |first1=L. |title=Possibilities of producing superheavy nuclei in multinucleon transfer reac-tions based on radioactive targets |journal=Chinese Physics C |date=2019 |volume=43 |issue=12 |pages=124103-1–124103-4 |doi=10.1088/1674-1137/43/12/124103 |bibcode=2019ChPhC..43l4103Z |s2cid=209932076 |url=http://hepnp.ihep.ac.cn/fileZGWLC/journal/article/zgwlc/newcreate/CPC-2019-0269.pdf |access-date=3 November 2019 |archive-date=3 November 2019 |archive-url=https://web.archive.org/web/20191103005211/http://hepnp.ihep.ac.cn/fileZGWLC/journal/article/zgwlc/newcreate/CPC-2019-0269.pdf |url-status=dead }} A 2018 study of the ²³⁸U + ²³²Th reaction at the Texas A&M Cyclotron Institute by Sara Wuenschel et al. found several unknown alpha decays that may possibly be attributed to new, neutron-rich isotopes of superheavy elements with 104 < Z < 116, though further research is required to unambiguously determine the atomic number of the products. This result strongly suggests that shell effects have a significant influence on cross sections, and that the island of stability could possibly be reached in future experiments with transfer reactions.{{cite journal |last1=Wuenschel |first1=S. |last2=Hagel |first2=K. |last3=Barbui |first3=M. |last4=Gauthier |first4=J. |last5=Cao |first5=X. G. |last6=Wada |first6=R. |last7=Kim |first7=E. J. |last8=Majka |first8=Z. |last9=Planeta |first9=R. |last10=Sosin |first10=Z. |last11=Wieloch |first11=A. |last12=Zelga |first12=K. |last13=Kowalski |first13=S. |last14=Schmidt |first14=K. |last15=Ma |first15=C. |last16=Zhang |first16=G. |last17=Natowitz |first17=J. B. |display-authors=3 |title=An experimental survey of the production of alpha decaying heavy elements in the reactions of ²³⁸U + ²³²Th at 7.5-6.1 MeV/nucleon |journal=Physical Review C |date=2018 |volume=97 |issue=6 |pages=064602-1–064602-12 |doi=10.1103/PhysRevC.97.064602 |arxiv=1802.03091 |bibcode=2018PhRvC..97f4602W|s2cid=67767157 }}

{{see also|Extended periodic table}}

Further shell closures beyond the main island of stability in the vicinity of Z = 112–114 may give rise to additional islands of stability. Although predictions for the location of the next magic numbers vary considerably, two significant islands are thought to exist around heavier doubly magic nuclei; the first near ³⁵⁴126 (with 228 neutrons) and the second near ⁴⁷²164 or ⁴⁸²164 (with 308 or 318 neutrons).{{cite journal|last=Greiner|first=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|pages=012002-1–012002-9|doi=10.1088/1742-6596/413/1/012002|bibcode=2013JPhCS.413a2002G|doi-access=free}} Nuclides within these two islands of stability might be especially resistant to spontaneous fission and have alpha decay half-lives measurable in years, thus having comparable stability to elements in the vicinity of flerovium. Other regions of relative stability may also appear with weaker proton shell closures in beta-stable nuclides; such possibilities include regions near ³⁴²126 and ⁴⁶²154.{{cite web|last1=Maly|first1=J.|last2=Walz|first2=D. R.|title=Search for superheavy elements among fossil fission tracks in zircon|date=1980|url=http://www.slac.stanford.edu/pubs/slacpubs/2500/slac-pub-2554.pdf |citeseerx=10.1.1.382.8189 |page=15}} Substantially greater electromagnetic repulsion between protons in such heavy nuclei may greatly reduce their stability, and possibly restrict their existence to localized islands in the vicinity of shell effects.{{cite journal |last1=Afanasjev |first1=A. F. |last2=Agbemava |first2=S. E. |last3=Gyawali |first3=A. |title=Hyperheavy nuclei: Existence and stability |date=2018 |journal=Physics Letters B |volume=782 |pages=533–540 |doi=10.1016/j.physletb.2018.05.070 |arxiv=1804.06395 |bibcode=2018PhLB..782..533A |s2cid=119460491 |url=https://www.researchgate.net/publication/324584302}} This may have the consequence of isolating these islands from the main chart of nuclides, as intermediate nuclides and perhaps elements in a "sea of instability" would rapidly undergo fission and essentially be nonexistent. It is also possible that beyond a region of relative stability around element 126, heavier nuclei would lie beyond a fission threshold given by the liquid drop model and thus undergo fission with very short lifetimes, rendering them essentially nonexistent even in the vicinity of greater magic numbers.{{cite journal|last=Okunev|first=V. S.|date=2018|title=About islands of stability and limiting mass of the atomic nuclei|journal=IOP Conference Series: Materials Science and Engineering|volume=468|pages=012012-1–012012-13|doi=10.1088/1757-899X/468/1/012012|url=https://www.researchgate.net/publication/329664372|doi-access=free}}

It has also been posited that in the region beyond A > 300, an entire "continent of stability" consisting of a hypothetical phase of stable quark matter, comprising freely flowing up and down quarks rather than quarks bound into protons and neutrons, may exist. Such a form of matter is theorized to be a ground state of baryonic matter with a greater binding energy per baryon than nuclear matter, favoring the decay of nuclear matter beyond this mass threshold into quark matter. If this state of matter exists, it could possibly be synthesized in the same fusion reactions leading to normal superheavy nuclei, and would be stabilized against fission as a consequence of its stronger binding that is enough to overcome Coulomb repulsion.{{cite journal |last1=Holdom |first1=B. |last2=Ren |first2=J. |last3=Zhang |first3=C. |title=Quark matter may not be strange |date=2018 |journal=Physical Review Letters |volume=120 |issue=1 |pages=222001-1–222001-6 |doi=10.1103/PhysRevLett.120.222001|pmid=29906186 |arxiv=1707.06610 |bibcode=2018PhRvL.120v2001H |s2cid=49216916 }}

{{Portal|Nuclear technology|physics}}

• Island of inversion
• Table of nuclides

{{notelist}}

{{Reflist|colwidth=30em}}

{{Refbegin}}

• {{cite book|last=Emsley|first=J.|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|year=2011|publisher=Oxford University Press|isbn=978-0-19-960563-7}}
• {{cite book |last1=Hoffman |first1=D. C. |author-link1=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=978-1-78326-244-1 |ref={{harvid|Hoffman|2000}}}}
• {{cite book |last=Kragh |first=H. |year=2018 |title=From Transuranic to Superheavy Elements: A Story of Dispute and Creation |publisher=Springer |isbn=978-3-319-75813-8}}
• {{cite book |editor1-last=Lodhi |editor1-first=M. A. K. |title=Superheavy Elements: Proceedings of the International Symposium on Superheavy Elements |publisher=Pergamon Press |date=1978 |isbn=978-0-08-022946-1 }}
• {{cite book |last=Podgorsak |first=E. B. |title=Radiation physics for medical physicists |year=2016 |publisher=Springer |isbn=978-3-319-25382-4 |edition=3rd}}

{{Refend}}

• [https://www.nature.com/articles/442876a Island ahoy!] (Nature, 2006, with JINR diagram of heavy nuclides and predicted island of stability)
• [http://curious.astro.cornell.edu/physics/85-the-universe/supernovae/general-questions/198-can-superheavy-elements-such-as-z-116-or-118-be-formed-in-a-supernova-can-we-observe-them-advanced Can superheavy elements (such as Z = 116 or 118) be formed in a supernova? Can we observe them?] (Cornell, 2004 – "maybe")
• [http://cerncourier.com/cws/article/cern/28509 Second postcard from the island of stability] (CERN, 2001; nuclides with 116 protons and mass 292)
• [http://cerncourier.com/cws/article/cern/28067 First postcard from the island of nuclear stability] (CERN, 1999; first few Z = 114 atoms)

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