Editing Flerovium (section)

===Nuclear stability and isotopes===
{{main|Isotopes of flerovium}}
[[File:IBA nuclear shells.svg|thumb|right|upright=1.6|Regions of differently shaped nuclei, as predicted by the [[interacting boson model]]<ref name="Kratz" />]]
The basis of the chemical [[periodic trends|periodicity]] in the periodic table is the electron shell closure at each noble gas ([[atomic number]]s [[helium|2]], [[neon|10]], [[argon|18]], [[krypton|36]], [[xenon|54]], [[radon|86]], and [[oganesson|118]]): as any further electrons must enter a new shell with higher energy, closed-shell electron configurations are markedly more stable, hence the inertness of noble gases.<ref name="Fricke1971" /> Protons and neutrons are also known to form closed nuclear shells, so the same happens at nucleon shell closures, which happen at specific nucleon numbers often dubbed "magic numbers". The known magic numbers are 2, 8, 20, 28, 50, and 82 for protons and neutrons; also 126 for neutrons.<ref name="Fricke1971" /> Nuclei with magic proton and [[neutron number]]s, such as [[helium-4]], [[oxygen-16]], [[calcium-48]], and [[lead-208]], are "doubly magic" and are very stable. This stability is very important for [[superheavy element]]s: with no stabilization, half-lives would be expected by exponential extrapolation to be [[nanosecond]]s at [[darmstadtium]] (element 110), because the ever-increasing electrostatic repulsion between protons overcomes the limited-range [[strong nuclear force]] that holds nuclei together. The next closed nucleon shells (magic numbers) are thought to denote the centre of the long-sought island of stability, where half-lives to alpha decay and spontaneous fission lengthen again.<ref name="Fricke1971" />

[[File:Next proton shell.svg|thumb|right|upright=1.6|Orbitals with high [[azimuthal quantum number]] are raised in energy, eliminating what would otherwise be a gap in orbital energy corresponding to a closed proton shell at element 114. This raises the next proton shell to the region around [[unbinilium|element 120]].<ref name="Kratz" />]]
Initially, by analogy with neutron magic number 126, the next proton shell was also expected at [[unbihexium|element 126]], too far beyond the synthesis capabilities of the mid-20th century to get much theoretical attention. In 1966, new values for the potential and [[spin–orbit interaction]] in this region of the periodic table<ref>{{Cite book|last1=Kalinkin|first1=B. N.|last2=Gareev|first2=F. A.|arxiv=nucl-th/0111083v2|title=Synthesis of Superheavy elements and Theory of Atomic Nucleus|date=2001|doi=10.1142/9789812777300_0009|journal=Exotic Nuclei|pages=118|isbn=978-981-238-025-8|bibcode=2002exnu.conf..118K|citeseerx=10.1.1.264.7426|s2cid=119481840}}</ref> contradicted this and predicted that the next proton shell would instead be at element 114,<ref name="Fricke1971" /> and that nuclei in this region would be relatively stable against spontaneous fission.<ref name="Fricke1971" /> The expected closed neutron shells in this region were at neutron number 184 or 196, making <sup>298</sup>Fl and <sup>310</sup>Fl candidates for being doubly magic.<ref name="Fricke1971" /> 1972 estimates predicted a half-life of around 1&nbsp;year for <sup>298</sup>Fl, which was expected to be near an [[island of stability]] centered near <sup>294</sup>Ds (with a half-life around 10<sup>10</sup>&nbsp;years, comparable to <sup>232</sup>[[thorium|Th]]).<ref name="Fricke1971" /> After making the first isotopes of elements 112–118 at the turn of the 21st century, it was found that these neutron-deficient isotopes were stabilized against fission. In 2008 it was thus hypothesized that the stabilization against fission of these nuclides was due to their [[Spheroid|oblate]] nuclei, and that a region of oblate nuclei was centred on <sup>288</sup>Fl. Also, new theoretical models showed that the expected energy gap between the proton orbitals 2f<sub>7/2</sub> (filled at element 114) and 2f<sub>5/2</sub> (filled at [[unbinilium|element 120]]) was smaller than expected, so element 114 no longer appeared to be a stable spherical closed nuclear shell. The next doubly magic nucleus is now expected to be around <sup>306</sup>Ubb, but this nuclide's expected short half-life and low production [[cross section (physics)|cross section]] make its synthesis challenging.<ref name="Kratz" /> Still, the island of stability is expected to exist in this region, and nearer its centre (which has not been approached closely enough yet) some nuclides, such as <sup>291</sup>[[moscovium|Mc]] and its alpha- and beta-decay [[decay product|daughters]],{{efn|Specifically, <sup>291</sup>Mc, <sup>291</sup>Fl, <sup>291</sup>Nh, <sup>287</sup>Nh, <sup>287</sup>Cn, <sup>287</sup>Rg, <sup>283</sup>Rg, and <sup>283</sup>Ds, which are expected to decay to the relatively longer-lived nuclei <sup>283</sup>Mt, <sup>287</sup>Ds, and <sup>291</sup>Cn.<ref name="Zagrebaev" />}} may be found to decay by [[positron emission]] or [[electron capture]] and thus move into the centre of the island.<ref name="Zagrebaev">{{cite conference|last1=Zagrebaev|first1=Valeriy|last2=Karpov|first2=Alexander|last3=Greiner|first3=Walter|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|url=http://iopscience.iop.org/1742-6596/420/1/012001/pdf/1742-6596_420_1_012001.pdf|access-date=20 August 2013}}</ref> Due to the expected high fission barriers, any nucleus in this island of stability would decay exclusively by alpha decay and perhaps some electron capture and [[beta decay]],<ref name="Fricke1971" /> both of which would bring the nuclei closer to the beta-stability line where the island is expected to be. Electron capture is needed to reach the island, which is problematic because it is not certain that electron capture is a major decay mode in this region of the [[chart of nuclides]].<ref name="Zagrebaev" />

Experiments were done in 2000–2004 at Flerov Laboratory of Nuclear Reactions in Dubna studying the fission properties of the compound nucleus <sup>292</sup>Fl by bombarding <sup>244</sup>Pu with accelerated <sup>48</sup>Ca ions.<ref name="jinr20006" /> A compound nucleus is a loose combination of [[nucleon]]s that have not yet arranged themselves into nuclear shells. It has no internal structure and is held together only by the collision forces between the two nuclei.<ref name="compoundnucleus" />{{efn|It is estimated that it requires around 10<sup>−14</sup>&nbsp;s for the nucleons to arrange themselves into nuclear shells, at which point the compound nucleus becomes a [[nuclide]], and this number is used by IUPAC as the minimum half-life a claimed isotope must have to be recognized as a nuclide.<ref name="compoundnucleus">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|date=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7|page=590}}</ref>}} Results showed how such nuclei fission mainly by expelling doubly magic or nearly doubly magic fragments such as <sup>40</sup>[[calcium|Ca]], <sup>132</sup>[[tin|Sn]], <sup>208</sup>[[lead|Pb]], or <sup>209</sup>[[bismuth|Bi]]. It was also found that <sup>48</sup>Ca and <sup>58</sup>[[iron|Fe]] projectiles had a similar yield for the fusion-fission pathway, suggesting possible future use of <sup>58</sup>Fe projectiles in making superheavy elements.<ref name="jinr20006">
{{cite web
|title=JINR Annual Reports 2000–2006
|url=http://www1.jinr.ru/Reports/Reports_eng_arh.html
|publisher=[[Joint Institute for Nuclear Research|JINR]]
|access-date=27 August 2013
}}</ref> It has also been suggested that a neutron-rich flerovium isotope can be formed by quasifission (partial fusion followed by fission) of a massive nucleus.<ref name="ZG" /> Recently it has been shown that multi-nucleon transfer reactions in collisions of actinide nuclei (such as [[uranium]] and [[curium]]) might be used to make neutron-rich superheavy nuclei in the island of stability,<ref name="ZG">
{{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|page=034610
|arxiv=0807.2537
|bibcode=2008PhRvC..78c4610Z
|doi=10.1103/PhysRevC.78.034610
}}</ref> though production of neutron-rich [[nobelium]] or [[seaborgium]] is more likely.<ref name="Zagrebaev" />

Theoretical estimates of alpha decay half-lives of flerovium isotopes, support the experimental data.<ref name="half-lifes">
{{cite journal
|last1=Chowdhury|first1=P. R.
|last2=Samanta|first2=C.
|last3=Basu|first3=D. N.
|date=2006
|title=α decay half-lives of new superheavy elements
|journal=[[Physical Review C]]
|volume=73|issue=1|page=014612
|arxiv=nucl-th/0507054
|bibcode=2006PhRvC..73a4612C
|doi=10.1103/PhysRevC.73.014612
|s2cid=118739116
}}</ref><ref>
{{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
}}</ref>
The fission-survived isotope <sup>298</sup>Fl, long expected to be doubly magic, is predicted to have alpha decay half-life ~17 days.<ref name="prc08">
{{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|page=044603
|arxiv=0802.3837
|bibcode=2008PhRvC..77d4603C
|doi=10.1103/PhysRevC.77.044603
|s2cid=119207807
}}</ref><ref>
{{cite journal
|last1=Roy Chowdhury|first1=P.
|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
}}</ref> Making <sup>298</sup>Fl directly by a fusion–evaporation pathway is currently impossible: no known combination of target and stable projectile can give 184 neutrons for the compound nucleus, and radioactive projectiles such as <sup>50</sup>Ca (half-life 14&nbsp;s) cannot yet be used in the needed quantity and intensity.<ref name="ZG" /> One possibility for making the theorized long-lived nuclei of copernicium (<sup>291</sup>Cn and <sup>293</sup>Cn) and flerovium near the middle of the island, is using even heavier targets such as <sup>250</sup>[[curium|Cm]], <sup>249</sup>[[berkelium|Bk]], <sup>251</sup>[[californium|Cf]], and <sup>254</sup>[[einsteinium|Es]], that when fused with <sup>48</sup>Ca would yield isotopes such as <sup>291</sup>Mc and <sup>291</sup>Fl (as decay products of <sup>299</sup>Uue, <sup>295</sup>Ts, and <sup>295</sup>Lv), which may have just enough neutrons to alpha decay to nuclides close enough to the centre of the island to possibly undergo electron capture and move inward to the centre. However, reaction cross sections would be small and little is yet known about the decay properties of superheavies near the beta-stability line. This may be the current best hope to synthesize nuclei in the island of stability, but it is speculative and may or may not work in practice.<ref name="Zagrebaev" /> Another possibility is to use controlled [[nuclear explosion]]s to get the high [[neutron flux]] needed to make macroscopic amounts of such isotopes.<ref name="Zagrebaev" /> This would mimic the [[r-process]] where the actinides were first produced in nature and the gap of instability after [[polonium]] bypassed, as it would bypass the gaps of instability at <sup>258–260</sup>[[fermium|Fm]] and at [[mass number]] 275 (atomic numbers [[rutherfordium|104]] to 108).<ref name="Zagrebaev" /> Some such isotopes (especially <sup>291</sup>Cn and <sup>293</sup>Cn) may even have been synthesized in nature, but would decay far too quickly (with half-lives of only thousands of years) and be produced in far too small quantities (~10<sup>−12</sup> the abundance of lead) to be detectable today outside [[cosmic ray]]s.<ref name="Zagrebaev" />