Isotopes of oganesson

Short description: Nuclides with atomic number of 118 but with different mass numbers

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 only isotope to be synthesized was 294Og in 2002 and 2005; it has a half-life of 700 microseconds.

## Contents

* 1 List of isotopes
* 2 Nucleosynthesis
* 2.1 Target-projectile combinations leading to Z=118 compound nuclei
* 2.2 Cold fusion
* 2.2.1 208Pb(86Kr,xn)294-xOg
* 2.3 Hot fusion
* 2.3.1 249Cf(48Ca,xn)297-xOg (x=3)
* 2.3.2 250,251Cf(48Ca,xn)298,299-xOg
* 2.3.3 248Cm(50Ti,xn)298-xOg
* 3 Theoretical calculations
* 3.1 Theoretical calculations on evaporation cross sections
* 4 References

## List of isotopes

Nuclide
| Z | N | Isotopic mass (u)
[n 1][n 2] | Half-life
| Decay
mode
[n 3] | Daughter
isotope
| Spin and
parity

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294Og  | 118  | 176  | 294.21398(59)#  | 0.7(3) ms[1] | α  | 290Lv | 0+
SF (rare)  | (various)

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

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## Nucleosynthesis

### Target-projectile combinations leading to Z=118 compound nuclei

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

Target | Projectile | CN | Attempt result

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208Pb  | 86Kr | 294Og | Failure to date
238U  | 58Fe | 296Og | Reaction yet to be attempted
244Pu  | 54Cr | 298Og | 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 fusion

#### 208Pb(86Kr,xn)294-xOg

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.[2]

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.[3] 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.[4][5] 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.[6]

### Hot fusion

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

Following successful experiments utilizing calcium-48 projectiles and actinide targets to generate elements 114 and 116,[7] 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.[8]

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.[7]

From 1 October 2015 until 6 April 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) reaction was estimated.[11]

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

In the 2015–2016 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-xOg

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 calculations

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 sections

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

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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]

## References

1. ↑ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (1 March 2021). "The NUBASE2020 evaluation of nuclear physics properties *" (in English). Chinese Physics C, High Energy Physics and Nuclear Physics 45 (3): 030001. doi:10.1088/1674-1137/abddae. ISSN 1674-1137. Bibcode: 2021ChPhC..45c0001K.
2. ↑ 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.
3. ↑ Public Affairs Department (21 July 2001). "Results of element 118 experiment retracted". Berkeley Lab. http://enews.lbl.gov/Science-Articles/Archive/118-retraction.html.
4. ↑ Dalton, R. (2002). "Misconduct: The stars who fell to Earth". Nature 420 (6917): 728–729. doi:10.1038/420728a. PMID 12490902. Bibcode: 2002Natur.420..728D.
5. ↑ Element 118 disappears two years after it was discovered . Physicsworld.com. Retrieved on 2 April 2012.
6. ↑ Zagrebaev, Valeriy; Karpov, Alexander; Greiner, Walter (2013). "Future of superheavy element research: Which nuclei could be synthesized within the next few years?". Journal of Physics 420 (1): 012001. doi:10.1088/1742-6596/420/1/012001. Bibcode: 2013JPhCS.420a2001Z. http://nrv.jinr.ru/pdf_file/J_phys_2013.pdf.
7. ↑ 7.0 7.1 Oganessian, Y.T. (2015). "Super-heavy element research". Reports on Progress in Physics 78 (3): 036301. doi:10.1088/0034-4885/78/3/036301. PMID 25746203. Bibcode: 2015RPPh...78c6301O. https://www.researchgate.net/publication/273327193.
8. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `synthesis-118-116`
9. ↑ "Ununoctium". WebElements Periodic Table. http://www.webelements.com/webelements/elements/text/Uuo/key.html.
10. ↑ Jacoby, Mitch (17 October 2006). "Element 118 Detected, With Confidence". Chemical & Engineering News 84 (43): 11. doi:10.1021/cen-v084n043.p011. https://pubs.acs.org/cen/news/84/i43/8443element118.html. Retrieved 18 January 2008. ""I would say we're very confident."".
11. ↑ 11.0 11.1 Voinov, A.A. (2018). "Study of the 249-251Cf + 48Ca reactions: recent results and outlook". Journal of Physics: Conference Series 966 (1): 012057. doi:10.1088/1742-6596/966/1/012057. Bibcode: 2018JPhCS.966a2057V. https://www.researchgate.net/publication/318324354.
12. ↑ Roberto, J. B. (31 March 2015). "Actinide Targets for Super-Heavy Element Research". Texas A & M University. http://cyclotron.tamu.edu/she2015/assets/pdfs/presentations/Roberto_SHE_2015_TAMU.pdf.
13. ↑ Hauschild, K. (26 June 2019). "Superheavy nuclei at RIKEN, Dubna, and JYFL". Conseil Scientifique de l'IN2P3. https://in2p3.cnrs.fr/sites/institut_in2p3/files/page/2019-07/6-Pres-HAUSCHILD_-compressé.pdf. Retrieved 31 July 2019.
14. ↑ Hauschild, K. (2019). "Heavy nuclei at RIKEN, Dubna, and JYFL". Conseil Scientifique de l'IN2P3. https://in2p3.cnrs.fr/sites/institut_in2p3/files/page/2019-07/6-Doc-HAUSCHILD-comp.pdf. Retrieved 1 August 2019.
15. ↑ 15.0 15.1 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. doi:10.1103/PhysRevC.73.014612. Bibcode: 2006PhRvC..73a4612C. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRVCAN000073000001014612000001&idtype=cvips&gifs=yes. 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. doi:10.1016/j.nuclphysa.2007.04.001. Bibcode: 2007NuPhA.789..142S.
17. ↑ 17.0 17.1 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. doi:10.1016/j.nuclphysa.2003.11.010. Bibcode: 2004NuPhA.730..355R.
18. ↑ S. B. Duarte; O. A. P. Tavares; M. Gonçalves; O. Rodríguez; F. Guzmán; T. N. Barbosa; F. García; A. Dimarco (2004). "Half-life predictions for decay modes of superheavy nuclei". Journal of Physics G: Nuclear and Particle Physics 30 (10): 1487–1494. doi:10.1088/0954-3899/30/10/014. Bibcode: 2004JPhG...30.1487D.
19. ↑ 19.0 19.1 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. doi:10.1103/PhysRevC.76.044606. Bibcode: 2007PhRvC..76d4606F.
20. ↑ 20.0 20.1 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): 35. doi:10.1140/epja/i2016-16035-0. Bibcode: 2016EPJA...52...35L.
21. ↑ 21.0 21.1 21.2 Feng, Z; Jin, G; Li, J; Scheid, W (2009). "Production of heavy and superheavy nuclei in massive fusion reactions". Nuclear Physics A 816 (1–4): 33–51. doi:10.1016/j.nuclphysa.2008.11.003. Bibcode: 2009NuPhA.816...33F.

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