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Oganesson (118Og) is a synthetic element created in particle accelerators, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first (and so far only) isotope to be synthesized was 294Og in 2002 and 2005; it has a half-life of 0.7 milliseconds. An unconfirmed isotope, 295Og, may have been observed in 2011 with a longer half-life of 181 milliseconds.

Main isotopes of oganesson (118Og)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
294Og[1] syn 0.7 ms α 290Lv
SF
295Og[2] syn 181 ms? α 291Lv

List of isotopesEdit

Nuclide
Z N Isotopic mass (u)
[n 1][n 2]
Half-life
Decay
mode

[n 3]
Daughter
isotope

Spin and
parity
294Og 118 176 294.21392(71)# 0.7 ms α 290Lv 0+
SF (various)
295Og[n 4] 118 177 295.21624(69)# 181 ms[2] α 291Lv
  1. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  3. ^ Modes of decay:
    SF: Spontaneous fission
  4. ^ Not directly synthesized, occurs in decay chain of 299Ubn; unconfirmed

NucleosynthesisEdit

Target-projectile combinations leading to Z=118 compound nucleiEdit

The below table contains various combinations of targets and projectiles that could be used to form compound nuclei with Z=118.

Target Projectile CN Attempt result
208Pb 86Kr 294Og Failure to date
238U 58Fe 296Og Reaction yet to be attempted
248Cm 50Ti 298Og Failure to date
250Cm 50Ti 300Og Reaction yet to be attempted
249Cf 48Ca 297Og Successful reaction
250Cf 48Ca 298Og Failure to date
251Cf 48Ca 299Og Failure to date
252Cf 48Ca 300Og Reaction yet to be attempted

Cold fusionEdit

208Pb(86Kr,xn)294-xOgEdit

In 1999, a team led by Victor Ninov at the Lawrence Berkeley National Laboratory performed this experiment, as a 1998 calculation by Robert Smolańczuk suggested a promising outcome. After eleven days of irradiation, three events of 293Og and its alpha decay products were reported in this reaction; this was the first reported discovery of element 118 and then-unknown element 116.[3]

The following year, they published a retraction after researchers at other laboratories were unable to duplicate the results and the Berkeley lab could not duplicate them either.[4] In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by principal author Victor Ninov.[5][6] Newer experimental results and theoretical predictions have confirmed the exponential decrease in cross-sections with lead and bismuth targets as the atomic number of the resulting nuclide increases.[7]

Hot fusionEdit

249Cf(48Ca,xn)297-xOg (x=3)Edit

Following successful experiments utilizing calcium-48 projectiles and actinide targets to generate elements 114 and 116,[8] the search for element 118 was first performed at the Joint Institute for Nuclear Research (JINR) in 2002. One or two atoms of 294Og were produced in the 2002 experiment, and two more atoms were produced in a 2005 confirmation run. The discovery of element 118 was announced in 2006.[1]

Because of the very small fusion reaction probability (the fusion cross section is ~0.3–0.6 pb), the experiment took four months and involved a beam dose of 2.5×1019 calcium ions that had to be shot at the californium target to produce the first recorded event believed to be the synthesis of oganesson.[9] Nevertheless, researchers were highly confident that the results were not a false positive; the chance that they were random events was estimated to be less than one part in 100,000.[10]

In a 2012 experiment aimed at the confirmation of tennessine, one alpha decay chain was attributed to 294Og. This synthesis event resulted from the population of 249Cf in the target as the decay product of the 249Bk target (half-life 330 days); the cross section and decays were consistent with previously reported observations of 294Og.[8]

From October 1, 2015 until April 6, 2016, the team at the JINR conducted a search for new isotopes of oganesson using a 48Ca beam and a target comprising a mixture of 249Cf (50.7%), 250Cf (12.9%), and 251Cf (36.4%). The experiment was performed at 252 MeV and 258 MeV beam energies. One event of 294Og was found at the lower beam energy, while no decays of oganesson isotopes were found at the higher beam energy; a cross section of 0.9 pb for the 249Cf(48Ca,3n) was estimated.[11]

250,251Cf(48Ca,xn)298,299-xOgEdit

In the same experiment, these reactions were performed in a search for 295Og and 296Og. No events attributable to a reaction with the 250Cf or 251Cf portions of the target were found. A repeat of this experiment was planned for 2017-2018.[11]

248Cm(50Ti,xn)298-xOgEdit

This reaction was originally planned to be tested at the JINR and RIKEN in 2017–2018, as it uses the same 50Ti projectile as planned experiments leading to elements 119 and 120.[12] A search beginning in summer 2016 at RIKEN for 295Og in the 3n channel of this reaction was unsuccessful, though the study is planned to resume; a detailed analysis and cross section limit were not provided.[13][14]

Theoretical calculationsEdit

Theoretical calculations done on the synthetic pathways for, and the half-life of, other isotopes have shown that some could be slightly more stable than the synthesized isotope 294Og, most likely 293Og, 295Og, 296Og, 297Og, 298Og, 300Og and 302Og.[15][16][17] Of these, 297Og might provide the best chances for obtaining longer-lived nuclei,[15][17] and thus might become the focus of future work with this element. Some isotopes with many more neutrons, such as some located around 313Og, could also provide longer-lived nuclei.[18]

Theoretical calculations on evaporation cross sectionsEdit

The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.

DNS = Di-nuclear system; 2S = Two-step; σ = cross section

Target Projectile CN Channel (product) σ max Model Ref
208Pb 86Kr 294Og 1n (293Og) 0.1 pb DNS [19]
208Pb 85Kr 293Og 1n (292Og) 0.18 pb DNS [19]
246Cm 50Ti 296Og 3n (293Og) 40 fb 2S [20]
244Cm 50Ti 294Og 2n (292Og) 53 fb 2S [20]
252Cf 48Ca 300Og 3n (297Og) 1.2 pb DNS [21]
251Cf 48Ca 299Og 3n (296Og) 1.2 pb DNS [21]
249Cf 48Ca 297Og 3n (294Og) 0.3 pb DNS [21]

ReferencesEdit

  • Isotope masses from:
    • M. Wang; G. Audi; A. H. Wapstra; F. G. Kondev; M. MacCormick; X. Xu; et al. (2012). "The AME2012 atomic mass evaluation (II). Tables, graphs and references" (PDF). Chinese Physics C. 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003.
    • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  1. ^ a b Oganessian, Yu. Ts.; Utyonkov, V. K.; Lobanov, Yu. V.; Abdullin, F. Sh.; Polyakov, A. N.; Sagaidak, R. N.; Shirokovsky, I. V.; Tsyganov, Yu. S.; et al. (2006-10-09). "Synthesis of the isotopes of elements 118 and 116 in the 249Cf and 245Cm+48Ca fusion reactions". Physical Review C. 74 (4): 044602. Bibcode:2006PhRvC..74d4602O. doi:10.1103/PhysRevC.74.044602. Retrieved 2008-01-18.
  2. ^ a b Hofmann, S.; Heinz, S.; Mann, R.; Maurer, J.; Münzenberg, G.; Antalic, S.; Barth, W.; Burkhard, H. G.; Dahl, L.; Eberhardt, K.; Grzywacz, R.; Hamilton, J. H.; Henderson, R. A.; Kenneally, J. M.; Kindler, B.; Kojouharov, I.; Lang, R.; Lommel, B.; Miernik, K.; Miller, D.; Moody, K. J.; Morita, K.; Nishio, K.; Popeko, A. G.; Roberto, J. B.; Runke, J.; Rykaczewski, K. P.; Saro, S.; Schneidenberger, C.; Schött, H. J.; Shaughnessy, D. A.; Stoyer, M. A.; Thörle-Pospiech, P.; Tinschert, K.; Trautmann, N.; Uusitalo, J.; Yeremin, A. V. (2016). "Remarks on the Fission Barriers of SHN and Search for Element 120". In Peninozhkevich, Yu. E.; Sobolev, Yu. G. (eds.). Exotic Nuclei: EXON-2016 Proceedings of the International Symposium on Exotic Nuclei. Exotic Nuclei. pp. 155–164. ISBN 9789813226555.
  3. ^ Hoffman, D.C; Ghiorso, A.; Seaborg, G.T. (2000). The Transuranium People: The Inside Story. Imperial College Press. pp. 425–431. ISBN 978-1-86094-087-3.
  4. ^ Public Affairs Department (21 July 2001). "Results of element 118 experiment retracted". Berkeley Lab. Archived from the original on 29 January 2008. Retrieved 18 January 2008.
  5. ^ Dalton, R. (2002). "Misconduct: The stars who fell to Earth". Nature. 420 (6917): 728–729. Bibcode:2002Natur.420..728D. doi:10.1038/420728a. PMID 12490902.
  6. ^ Element 118 disappears two years after it was discovered. Physicsworld.com. Retrieved on 2 April 2012.
  7. ^ Zagrebaev, Valeriy; Karpov, Alexander; Greiner, Walter (2013). "Future of superheavy element research: Which nuclei could be synthesized within the next few years?" (PDF). Journal of Physics. 420 (1): 012001. arXiv:1207.5700. Bibcode:2013JPhCS.420a2001Z. doi:10.1088/1742-6596/420/1/012001.
  8. ^ a b Oganessian, Y.T. (2015). "Super-heavy element research". Reports on Progress in Physics. 78 (3): 036301. Bibcode:2015RPPh...78c6301O. doi:10.1088/0034-4885/78/3/036301. PMID 25746203.
  9. ^ "Ununoctium". WebElements Periodic Table. Retrieved 2007-12-09.
  10. ^ Jacoby, Mitch (17 October 2006). "Element 118 Detected, With Confidence". Chemical & Engineering News. Retrieved 18 January 2008. I would say we're very confident.
  11. ^ a b Voinov, A.A.; et al. (2018). "Study of the 249-251Cf + 48Ca reactions: recent results and outlook". Journal of Physics: Conference Series. doi:10.1088/1742-6596/966/1/012057.
  12. ^ Roberto, J. B. (31 March 2015). "Actinide Targets for Super-Heavy Element Research" (PDF). cyclotron.tamu.edu. Texas A & M University. Retrieved 28 April 2017.
  13. ^ Hauschild, K. (26 June 2019). Superheavy nuclei at RIKEN, Dubna, and JYFL (PDF). Conseil Scientifique de l'IN2P3. Retrieved 31 July 2019.
  14. ^ Hauschild, K. (2019). Heavy nuclei at RIKEN, Dubna, and JYFL (PDF). Conseil Scientifique de l'IN2P3. Retrieved 1 August 2019.
  15. ^ a b P. Roy Chowdhury; C. Samanta; D. N. Basu (January 26, 2006). "α decay half-lives of new superheavy elements". Physical Review C. 73 (1): 014612. arXiv:nucl-th/0507054. Bibcode:2006PhRvC..73a4612C. doi:10.1103/PhysRevC.73.014612. Retrieved 2008-01-18.
  16. ^ C. Samanta; P. Roy Chowdhury; D. N. Basu (April 6, 2007). "Predictions of alpha decay half lives of heavy and superheavy elements". Nuclear Physics A. 789 (1–4): 142–154. arXiv:nucl-th/0703086. Bibcode:2007NuPhA.789..142S. CiteSeerX 10.1.1.264.8177. doi:10.1016/j.nuclphysa.2007.04.001. Archived from the original on February 1, 2013. Retrieved 2008-01-18.
  17. ^ a b G. Royer; K. Zbiri; C. Bonilla (2004). "Entrance channels and alpha decay half-lives of the heaviest elements". Nuclear Physics A. 730 (3–4): 355–376. arXiv:nucl-th/0410048. Bibcode:2004NuPhA.730..355R. doi:10.1016/j.nuclphysa.2003.11.010. Retrieved 2008-01-18.
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  19. ^ a b Feng, Zhao-Qing; Jin, Gen-Ming; Li, Jun-Qing; Scheid, Werner (2007). "Formation of superheavy nuclei in cold fusion reactions". Physical Review C. 76 (4): 044606. arXiv:0707.2588. Bibcode:2007PhRvC..76d4606F. doi:10.1103/PhysRevC.76.044606.
  20. ^ a b Liu, L.; Shen, C.; Li, Q.; Tu, Y.; Wang, X.; Wang, Y. (2016). "Residue cross sections of 50Ti-induced fusion reactions based on the two-step model". European Physical Journal A. 52 (35). arXiv:1512.06504. doi:10.1140/epja/i2016-16035-0.
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