نظائر الأوگانسون

نظائر oganesson (₁₁₈Og)
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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 only isotope to be synthesized was ²⁹⁴Og in 2002 and 2005; it has a half-life of 700 microseconds.

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List of isotopes

Nuclide	Z	N	Isotopic mass (Da)^[4] ^{[n 1]}^{[n 2]}	Half-life	Decay mode ^{[n 3]}	Daughter isotope	Spin and parity
²⁹⁴Og	118	176	294.21398(59)#	0.7(3) ms^[5]	α	²⁹⁰Lv	0+
²⁹⁴Og	118	176	294.21398(59)#	0.7(3) ms^[5]	SF (rare)	(various)	0+
This table header & footer: view

^ ( ) – 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).
^ أنماط الاضمحلال:

SF: Spontaneous fission

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.^{[بحاجة لمصدر]}

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

الاندماج البارد

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.^[6]

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.^[7] 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.^[8]^[9] 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.^[10]

الاندماج الساخن

²⁴⁹Cf(⁴⁸Ca,xn)^297-xOg (x=3)

Following successful experiments utilizing calcium-48 projectiles and actinide targets to generate elements 114 and 116,^[11] 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 2.5×10¹⁹ calcium ions that had to be shot at the californium target to produce the first recorded event believed to be the synthesis of oganesson.^[12] 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.^[13]

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.^[11]

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.^[14]

^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.^[14]

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.^[15] 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.^[16]^[17]

الحسابات النظرية

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.^[18]^[19]^[20] Of these, ²⁹⁷Og might provide the best chances for obtaining longer-lived nuclei,^[18]^[20] 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.^[21]

الحسابات النظرية حول مقاطع البخر

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	^[22]
²⁰⁸Pb	⁸⁵Kr	²⁹³Og	1n (²⁹²Og)	0.18 pb	DNS	^[22]
²⁴⁶Cm	⁵⁰Ti	²⁹⁶Og	3n (²⁹³Og)	40 fb	2S	^[23]
²⁴⁴Cm	⁵⁰Ti	²⁹⁴Og	2n (²⁹²Og)	53 fb	2S	^[23]
²⁵²Cf	⁴⁸Ca	³⁰⁰Og	3n (²⁹⁷Og)	1.2 pb	DNS	^[24]
²⁵¹Cf	⁴⁸Ca	²⁹⁹Og	3n (²⁹⁶Og)	1.2 pb	DNS	^[24]
²⁴⁹Cf	⁴⁸Ca	²⁹⁷Og	3n (²⁹⁴Og)	0.3 pb	DNS	^[24]