Unbinilium, Ubn, is the temporary name for element 120. Wikipedia has an article, Unbinilium, which addresses this element at length. This article focuses on topics Wikipedia does not: isotopes far from N = 184, which isotopes can actually form, and how long the element will be present.
There are a large number of neutron-rich Ubn isotopes which can form. All will disappear within 1000 sec after the event which led to their formation. There are also many isotopes near the N = 184 and N = 196 shell closures, but these cannot form, except by physicist-catalyzed reactions.
While this element can exist in nature as a nuclear phenomenon, its chemistry exists only in the laboratory.
Synthesis of Ubn has been reported, but not confirmed. It has been argued (see the Wikipedia article mentioned above) that Ubn may be the limit for current fusion-evaporation techniques.
Wikipedia's article "Ununennium" has a section addressing predicted nuclear properties, That section is limited to consideration of Uue isotopes with neutron counts near 184. This article focuses on isotopes not reported on by Wikipedia, It uses two main resources chosen because of their independence from one another. A third source furnishes quantitative information over a more limited range.
At least one document maps half-life and decay mode for elements below Z = 175 from the neutron dripline down to isotopes which are too neutron-poor to survive any appreciable length of time(1). Maps on pp 15 & 18 address the entire (Z,N) region covered, but report only the dominant decay mode and report half-lives only to within a band three orders of magnitude wide (0.001 - 1 sec, for example). More detailed estimates of these properties can be extracted from maps on pp 11 & 12, but only for a limited range of Z and N. Half-life data are reported by colors, which makes numerical estimates laborious to produce. This document is connected to Japan's KTUY model.
An independent map of half-lives and decay modes exists(2). This one is limited to A = 339, as well as to Z = 132. It does not show short-lived isotopes well, and gives half-lives only within rather broad and awkward bands. It does show multiple decay modes for single nuclides, although this feature is hard to read. It originates from models used by the Russian agency JINR, so is completely independent of Ref. 1.
Japan Atomic Energy Agency (JAEA) maintains an on-line chart of nuclides which includes decay properties of many predicted nuclides(3) - unlike charts published by Korea Atomic Energy Research Institute (KAERI) or the (U.S.) National Nuclear Data Center (NNDC). This chart gives separate numerical values for partial half-lives against fission, beta emission (both b- and b+), and alpha emission. These appear to be systematically too long, but are probably reliable to within an order of magnitude.
Even-N isotopes from the neutron dripline down to Ubn 385 decay predominantly by beta emission with half-lives in the 0.001 - 1 sec range. Half-lives aren't reported, but the properties of beta decay indicate that half-lives close to 0.001 sec are likely(4). Odd-N drops in this band decay by neutron emission.
All isotopes in the band Ubn 384 to Ubn 368 are predicted to have half-lives in the 0.001 - 1 sec range. Dominant decay modes are a mixture of fission and beta emission. Which mode dominates depends on N, with specific values of N associated with fission over a range of Z values. It is likely that both modes are significant for all isotopes.
Isotopes in the band Ubn 367 to Ubn 339 are predicted to decay by beta emission. With the exception of Ubn 342 to Ubn 340, all have half-lives in the 0.001 - 1 sec range. The exceptions probably have half-lives in the 1 - 10 sec range.
Ubn 338 to Ubn 335 are predicted to decay by fission and to have half-lives below 0.001 sec. Most are predicted to have very short half-lives..
Ref 1 predicts a gap from Ubn 334 to Ubn 317, which is predicted to be occupied by nuclear drops or very short-lived nuclides.
Ref, 2 reports isotopes with half-lives above 10^-06 sec in the band Ubn 318 - Ubn 315. Of these, Ubn 317 has a half-life in the 1 sec - 1 day band; and all others have half-lives in the 0.001 - 1 sec band. They are all predicted to decay by fission. Ref. 1 shows no sign of this stable zone. Ref 2 also shows Ubn 333 as having a half-life in the 10^-06 - 0.001 sec range, which extends the pattern shown in Fig. 1, but also requires a much longer half-life than that document indicates is possible.
Ref 1 predicts Ubn 315 to Ubn 310 will decay by quickly and by fission. Except for the long half-life predicted at Ubn 315, Ref. 2 agrees.
Ref. 1 predicts that Ubn 309 to Ubn 307 will decay by alpha emission with half-lives in the 10^-06 - 0.001 sec range. Ref. 2 indicates fission decay and shorter half-lives. Both Ref. 1 and Ref. 2 agree that Ubn 306 should decay by alpha emission with a sub-microsecond half-life.
Ref. 3 shows a dip in alpha-decay partial half-lives between Ubn 308 and Ubn 306. Above Ubn 308, the longer partial half-lives are masked by onset of rapid decay by fission. This band is located just above the shell closure at N = 184, where it is expected.
Below Ubn 306, studies of decay properties become more numerous. It is beyond the scope of this article to compare them or assess what the actual properties of Ubn isotopes may be. One thing which can be noted is the prediction in Ref. 3 that Ubn 303 and Ubn 299 will have the longest half-lives in this region, at around 0.01 sec.
The lightest isotope reported by any of Refs. 1 through3 is Ubn 283. There may be a few lighter nuclides with half-lives in the 10^-14 - 10^-09 sec range, but half-lives will quickly decline below the minimum needed for a nuclear drop to qualify as a nuclide.
All even-N isotopes from the neutron dripline to Ubn 385 can form, either directly as material is ejected from a disintegrating neutron star, as fission infall from larger nuclides, or by a chain of beta decays from directly-formed nuclides. All isotopes in the band Ubn 384 to Ubn 335 can form the same way, although direct formation is unlikely at lower N.
No isotopes lighter than Ubn 335 are likely to form. Beta-decay chains with proper A values starting near the neutron dripline are terminated by fission at Z < 120. Note that termination requires rapid decay by fission. Nuclides whose half-lives are comparable with beta-emission half-lives do not terminate beta-decay chains.
It is improbable that neutron capture can form any Ubn isotope.
All Ubn isotopes which can form have short half-lives and are the result of beta decay of short-lived nuclides. The element is expected to disappear completely less than 1000 sec after a neutron star merger of similar event which led to its formation.
Wikipedia's article "Unbinilium" addresses the element's atomic properties and chemistry in some detail. One point it does not make is that, while Ubn nuclei can form, they do not persist long enough to reach an environment cool enough to allow chemical processes. The chemistry of Uue is entirely synthetic.
1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011.
2. “Systematic Study of Decay Properties of Heaviest Elements.”; Y. M. Palenzuelaa, L. F. Ruiza, A. Karpov, and W. Greiner; Bulletin of the Russian Academy of Sciences, Physics. Vol . 76, No.11, pp 1165 – 1177; 2012
3. "Chart of the Nuclides, 2014", Japan Atomic Energy Agency; website available using "chart of nuclides" and "JAEA" as internet search terms.
4. "Nuclear Properties for Astrophysical Applications"; P. Moller & J. R. Nix; Los Alamos National Laboratory website; search by "LANL, T2", then "Nuclear Properties for Astrophysical Applications".
|9-Period Periodic Table of Elements|