Ununennium (₁₁₉Uue) has not yet been synthesised, so there is no experimental data and astandard atomic weight cannot be given. Like allsynthetic elements, it would have nostable isotopes.

No isotopes of ununennium are known.

The below table contains various combinations of targets and projectiles that could be used to form compound nuclei withZ = 119.^[1]

Following the claimed synthesis of²⁹³Og in 1999 at theLawrence Berkeley National Laboratory from²⁰⁸Pb and⁸⁶Kr, the analogous reactions²⁰⁹Bi +⁸⁶Kr and²⁰⁸Pb +⁸⁷Rb were proposed for the synthesis of element 119 and its then-unknown alpha decaydaughters, elements117,115, and113.^[3] The retraction of these results in 2001^[4] and more recent calculations on the cross sections for "cold" fusion reactions cast doubt on this possibility; for example, a maximum yield of 2fb is predicted for the production of²⁹⁴Uue in the former reaction.^[5] Radioactive ion beams may provide an alternative method utilizing alead orbismuth target, and may enable the production of more neutron-rich isotopes should they become available at required intensities.^[5]

There are indications that the team at theJoint Institute for Nuclear Research (JINR) in Russia plans to try this reaction in the future. The product of the 3n channel would be²⁹⁴Uue; its expected granddaughter²⁸⁶Mc was synthesised in a preparatory experiment at the JINR in 2021, using the reaction²⁴³Am(⁴⁸Ca,5n)²⁸⁶Mc.^[2]

The team at the Heavy Ion Research Facility inLanzhou (HIRFL), which is operated by theInstitute of Modern Physics (IMP) of theChinese Academy of Sciences, also plans to try the²⁴³Am+⁵⁴Cr reaction.^[6][7]

The team at RIKEN inWakō, Japan began bombardingcurium-248 targets with avanadium-51 beam in January 2018^[8] to search for element 119. Curium was chosen as a target, rather than heavierberkelium orcalifornium, as these heavier targets are difficult to prepare.^[9] The reduced asymmetry of the reaction is expected to approximately halve the cross section, requiring a sensitivity "on the order of at least 30 fb".^[10] The²⁴⁸Cm targets were provided byOak Ridge National Laboratory. RIKEN developed a high-intensity vanadium beam.^[11] The experiment began at a cyclotron while RIKEN upgraded its linear accelerators; the upgrade was completed in 2020.^[12] Bombardment may be continued with both machines until the first event is observed; the experiment is currently running intermittently for at least 100 days per year.^[13][9] The RIKEN team's efforts are being financed by theEmperor of Japan.^[14]

²⁴⁸
₉₆Cm +⁵¹
₂₃V →²⁹⁹
₁₁₉Uue* → no atoms yet

The produced isotopes of ununennium are expected to undergo two alpha decays to known isotopes ofmoscovium (²⁸⁸Mc and²⁸⁷Mc respectively),^[8] which would anchor them to a known sequence of five further alpha decays and corroborate their production. In 2022, the optimal reaction energy for synthesis of ununennium in this reaction was experimentally estimated as234.8±1.8 MeV at RIKEN.^[15] The cross section is probably below 10 fb.^[11]

As of September 2023, the team at RIKEN had run the²⁴⁸Cm+⁵¹V reaction for 462 days. A report by the RIKEN Nishina Center Advisory Committee noted that this reaction was chosen because of the availability of the target and projectile materials, despite predictions favoring the²⁴⁹Bk+⁵⁰Ti reaction, owing to the⁵⁰Ti projectile being closer to doubly magic⁴⁸Ca and having an even atomic number (22); reactions with even-Z projectiles have generally been shown to have greater cross-sections. The report recommended that if the 5 fb cross-section limit is reached without any events observed, then the team should "evaluate and eventually reconsider the experimental strategy before taking additional beam time."^[16] As of August 2024, the team at RIKEN was still running this reaction "24/7".^[17]

From April to September 2012, an attempt to synthesize the isotopes²⁹⁵Uue and²⁹⁶Uue was made by bombarding a target ofberkelium-249 withtitanium-50 at theGSI Helmholtz Centre for Heavy Ion Research inDarmstadt, Germany.^[18][19] This reaction between²⁴⁹Bk and⁵⁰Ti was predicted to be the most favorable practical reaction for formation of ununennium,^[19] as it is rather asymmetrical,^[20] though also somewhat cold.^[21] (The reaction between²⁵⁴Es and⁴⁸Ca would be superior, but preparing milligram quantities of²⁵⁴Es for a target is difficult.)^[20] Moreover, as berkelium-249 decays tocalifornium-249 (the next element) with a short half-life of 327 days, this allowed elements 119 and 120 to be searched for simultaneously.^[10] Nevertheless, the necessary change from the "silver bullet"⁴⁸Ca to⁵⁰Ti divides the expected yield of ununennium by about twenty, as the yield is strongly dependent on the asymmetry of the fusion reaction.^[20] Due to the predicted short half-lives, the GSI team used new "fast" electronics capable of registering decay events within microseconds.^[19][20]

²⁴⁹
₉₇Bk +⁵⁰
₂₂Ti →²⁹⁹
₁₁₉Uue* → no atoms

²⁴⁹
₉₈Cf +⁵⁰
₂₂Ti →²⁹⁹
₁₂₀Ubn* → no atoms

Neither element 119 nor element 120 was observed. This implied a limiting cross-section of 65 fb for producing element 119 in these reactions, and 200 fb for element 120.^[21][10] The predicted actual cross section for producing element 119 in this reaction is around 40 fb, which is at the limits of current technology.^[20] (The record lowest cross section of an experimentally successful reaction is 30 fb for the reaction between²⁰⁹Bi and⁷⁰Zn producingnihonium.)^[20] The experiment was originally planned to continue to November 2012,^[22] but was stopped early to make use of the²⁴⁹Bk target to confirm the synthesis oftennessine (thus changing the projectiles to⁴⁸Ca).^[21]

The team at theJoint Institute for Nuclear Research inDubna, Russia, planned to attempt this reaction.^{[23][24][25][26][27][28]}

The synthesis of ununennium was first attempted in 1985 by bombarding a sub-microgram target of einsteinium-254 withcalcium-48 ions at the superHILAC accelerator at Berkeley, California:

²⁵⁴
₉₉Es +⁴⁸
₂₀Ca →³⁰²
₁₁₉Uue* → no atoms

No atoms were identified, leading to a limitingcross section of 300nb.^[29] Later calculations suggest that the cross section of the 3n reaction (which would result in²⁹⁹Uue and three neutrons as products) would actually be six hundred thousand times lower than this upper bound, at 0.5 pb.^[30] Tens of milligrams of einsteinium, an amount that cannot presently be produced, would be needed for this reaction to have a reasonable chance of succeeding.^[11]

• Hoffman, D. C.;Ghiorso, A.; Seaborg, G. T. (2000).The Transuranium People: The Inside Story.World Scientific.ISBN 978-1-78-326244-1.
• Zagrebaev, V.; Karpov, A.; Greiner, W. (2013)."Future of superheavy element research: Which nuclei could be synthesized within the next few years?"(PDF).Journal of Physics: Conference Series.420 (1). 012001.arXiv:1207.5700.Bibcode:2013JPhCS.420a2001Z.doi:10.1088/1742-6596/420/1/012001.ISSN 1742-6588.S2CID 55434734. Archived fromthe original(PDF) on 2015-10-03. Retrieved2023-08-16.

• Radioisotopes
• Ununennium
• Lists of isotopes by element

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