Following the claimed synthesis of 293Og in 1999 at the Lawrence Berkeley National Laboratory from 208Pb and 86Kr, the analogous reactions 209Bi + 86Kr and 208Pb + 87Rb were proposed for the synthesis of element 119 and its then-unknown alpha decay daughters, elements 117, 115, and 113.[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 2 fb is predicted for the production of 294Uue in the former reaction.[5] Radioactive ion beams may provide an alternative method utilizing a lead or bismuth target, and may enable the production of more neutron-rich isotopes should they become available at required intensities.[5]
Hot fusion
243Am(54Cr,xn)297−xUue
There are indications that the team at the Joint Institute for Nuclear Research (JINR) in Russia plans to try this reaction in the future. The product of the 3n channel would be 294Uue; its expected granddaughter 286Mc was synthesised in a preparatory experiment at the JINR in 2021, using the reaction 243Am(48Ca,5n)286Mc.[2]
The team at RIKEN in Wakō, Japan began bombarding curium-248 targets with a vanadium-51 beam in January 2018[8] to search for element 119. Curium was chosen as a target, rather than heavier berkelium or californium, 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] The 248Cm targets were provided by Oak 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 the Emperor 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 of moscovium (288Mc and 287Mc 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 as 234.8±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 the 248Cm+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 the 249Bk+50Ti reaction, owing to the 50Ti projectile being closer to doubly magic 48Ca 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]
249Bk(50Ti,xn)299−xUue
From April to September 2012, an attempt to synthesize the isotopes 295Uue and 296Uue was made by bombarding a target of berkelium-249 with titanium-50 at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany.[18][19] This reaction between 249Bk and 50Ti 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 between 254Es and 48Ca would be superior, but preparing milligram quantities of 254Es for a target is difficult.)[20] Moreover, as berkelium-249 decays to californium-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 to 50Ti 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 between 209Bi and 70Zn producing nihonium.)[20] The experiment was originally planned to continue to November 2012,[22] but was stopped early to make use of the 249Bk target to confirm the synthesis of tennessine (thus changing the projectiles to 48Ca).[21]
The synthesis of ununennium was first attempted in 1985 by bombarding a sub-microgram target of einsteinium-254 with calcium-48 ions at the superHILAC accelerator at Berkeley, California:
254 99Es + 48 20Ca → 302 119Uue * → no atoms
No atoms were identified, leading to a limiting cross section of 300 nb.[29] Later calculations suggest that the cross section of the 3n reaction (which would result in 299Uue 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]
^Geng, Chang; Chen, Peng-Hui; Niu, Fei; Yang, Zu-Xing; Zeng, Xiang-Hua; Feng, Zhao-Qing (23 February 2024). "Assessing the Impact of Nuclear Mass Models on the Prediction of Synthesis Cross Sections for Superheavy Elements". arXiv:2402.15304v1 [nucl-th].
^Gan, Z. G.; Huang, W. X.; Zhang, Z. Y.; Zhou, X. H.; Xu, H. S. (2022). "Results and perspectives for study of heavy and super-heavy nuclei and elements at IMP/CAS". The European Physical Journal A. 58 (158). doi:10.1140/epja/s10050-022-00811-w.
^Sakurai, Hiroyoshi (1 April 2020). "Greeting | RIKEN Nishina Center". With the completion of the upgrade of the linear accelerator and BigRIPS at the beginning of 2020, the RNC aims to synthesize new elements from element 119 and beyond.
^Chapman, Kit; Turner, Kristy (13 February 2018). "The hunt is on". Education in Chemistry. Royal Society of Chemistry. Retrieved 28 June 2019. The hunt for element 113 was almost abandoned because of lack of resources, but this time Japan's emperor is bankrolling Riken's efforts to extend the periodic table to its eighth row.
^"Scientists will begin experiments on the synthesis of element 119 in 2019". jinr.ru. JINR. 28 September 2016. Retrieved 31 March 2017. "The discovery of elements 115, 117 and 118 is an accomplished fact; they were placed in the periodic table, though still unnamed and will be confirmed only at the end of the year. The D.I.Mendeleev Periodic Table is not infinite. In 2019, scientists will begin the synthesis of elements 119 and 120 which are the first in the 8th period," said S.N. Dmitriev.
