^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
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
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.[5]
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.[6] 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.[7][8] 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.[9]
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,[10] 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.[2]
Because of the very small
fusion reaction probability (the fusion
cross section is roughly 0.3–0.6
pb), the experiment took four months and involved a beam dose of 2.5×1019calcium ions that had to be shot at the
californium target to produce the first recorded event believed to be the synthesis of oganesson.[11]
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.[12]
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.[10]
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.[13]
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.[13]
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.[14] 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.[15][16]
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.[17][18][19] Of these, 297Og might provide the best chances for obtaining longer-lived nuclei,[17][19] 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.[20]
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.
^Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003.
doi:
10.1088/1674-1137/abddaf.
^Hoffman, D.C; Ghiorso, A.; Seaborg, G.T. (2000). The Transuranium People: The Inside Story. Imperial College Press. pp. 425–431.
ISBN978-1-86094-087-3.
^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.
Bibcode:
2004JPhG...30.1487D.
CiteSeerX10.1.1.692.3012.
doi:
10.1088/0954-3899/30/10/014.