Unbinilium

Unbinilium (pronounced /uːnbaɪˈnɪliəm/), also called eka-radium, is the temporary, systematic element name of a hypothetical chemical element in the periodic table that has the temporary symbol Ubn and has the atomic number 120. Since unbinilium is placed below the alkaline earth metals it possibly has properties similar to those of radium or barium.

Attempts to date to synthesize the element using fusion reactions at low excitation energy have met with failure, although there are reports that the fission of nuclei of unbinilium at very high excitation has been successfully measured, indicating a strong shell effect at Z=120.

Attempts at synthesis
Neutron evaporation

In March-April 2007, the synthesis of unbinilium was attempted at the Flerov Laboratory of Nuclear Reactions in Dubna by bombarding a plutonium-244 target with iron-58 ions.[1] Initial analysis revealed that no atoms of element 120 were produced providing a limit of 400 fb for the cross section at the energy studied.[2]

\( \,^{244}_{94}\mathrm{Pu} + \,^{58}_{26}\mathrm{Fe} \to \,^{302}_{120}\mathrm{Ubn} ^{*} \to \ fission\ \) only

The Russian team are planning to upgrade their facilities before attempting the reaction again.

In April 2007, the team at GSI attempted to create unbinilium using uranium-238 and nickel-64:

\( \,^{238}_{92}\mathrm{U} + \,^{64}_{28}\mathrm{Ni} \to \,^{302}_{120}\mathrm{Ubn} ^{*} \to \ fission \ \) only

No atoms were detected providing a limit of 1.6 pb on the cross section at the energy provided. The GSI repeated the experiment with higher sensitivity in three separate runs from April–May 2007, Jan–March 2008, and Sept–Oct 2008, all with negative results and providing a cross section limit of 90 fb.

Compound nucleus fission

Unbinilium is of interest because it is part of the hypothesized island of stability, with the compound nucleus 302Ubn being the most stable of those that can be created directly by current methods. It has been calculated that Z=120 may in fact be the next proton magic number, rather than at Z=114 or 126.

Several experiments have been performed between 2000–2008 at the Flerov laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus 302Ubn. Two nuclear reactions have been used, namely 244Pu+58Fe and 238U+64Ni. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as 132Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between 48Ca and 58Fe projectiles, indicating a possible future use of 58Fe projectiles in superheavy element formation.[3]

In 2008, the team at GANIL, France, described the results from a new technique which attempts to measure the fission half-life of a compound nucleus at high excitation energy, since the yields are significantly higher than from neutron evaporation channels. It is also a useful method for probing the effects of shell closures on the survivability of compound nuclei in the super-heavy region, which can indicate the exact position of the next proton shell (Z=114, 120, 124, or 126). The team studied the nuclear fusion reaction between uranium ions and a target of natural nickel:

\( \,^{238}_{92}\mathrm{U} + \,^{nat}_{28}\mathrm{Ni} \to \,^{296,298,299,300,302}\mathrm{Ubn} ^{*} \to \ \) fission.

The results indicated that nuclei of unbinilium were produced at high (~70 MeV) excitation energy which underwent fission with measurable half-lives > 10−18s. Although very short, the ability to measure such a process indicates a strong shell effect at Z=120. At lower excitation energy (see neutron evaporation), the effect of the shell will be enhanced and ground-state nuclei can be expected to have relatively long half-lives. This result could partially explain the relatively long half-life of 294Uuo measured in experiments at Dubna. Similar experiments have indicated a similar phenomenon at Z=124 (see unbiquadium) but not for ununquadium, suggesting that the next proton shell does in fact lie at Z>120.[4][5]
Future reactions

The GSI have plans to start up a program utilizing 248Cm targets for superheavy element production and will most likely attempt this reaction in 2010 or 2011.[6]

Likewise, the team at RIKEN have also begun a program utilizing 248Cm targets and have indicated future experiments to probe the possibility of Z=120 being the next magic number using the aforementioned nuclear reactions to form 302Ubn.[7]
Calculated decay characteristics

In a quantum tunneling model with mass estimates from a macroscopic-microscopic model, the alpha-decay half-lives of several isotopes of unbinilium (namely, 292-304Ubn) have been predicted to be around 1–20 microseconds.[8][9][10][11]
Extrapolated reactivity

Unbinilium should be highly reactive, according to periodic trends, as this element is a member of alkaline earth metals. It would be much more reactive than any other lighter elements of this group. If group reactivity is followed, this element would react violently in air to form an oxide (UbnO) and in water to form the hydroxide, which would be a strong base and highly explosive in terms of flammability. It is also possible that, due to relativistic effects, the element has noble gas character, as already seen for ununquadium. A predicted oxidation state is II.
Target-projectile combinations leading to Z=120 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 120.

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.

MD = multi-dimensional; DNS = dinuclear system; AS = advanced statistical; σ = cross section

Unbinilium in Popular Fiction

* A plot element in Meteor Storm, where unbinilium was the trace element in meteorites, causing disruption to electrical/electromagnetic systems due to its 'aggressive broadcasting of its frequency'.

See also

* Island of stability: ununquadium–unbinilium–unbihexium
* radium

References

1. ^ THEME03-5-1004-94/2009
2. ^ Oganessian et al. (2009). "Attempt to produce element 120 in the 244Pu+58Fe reaction". Phys. Rev. C 79: 024603. doi:10.1103/PhysRevC.73.014612.
3. ^ see Flerov lab annual reports 2000-2004
4. ^ Natowitz, Joseph (2008). "How stable are the heaviest nuclei?". Physics 1: 12. doi:10.1103/Physics.1.12.
5. ^ Morjean, M. et al. (2008). "Fission Time Measurements: A New Probe into Superheavy Element Stability". Phys. Rev. Lett. 101: 072701. doi:10.1103/PhysRevLett.101.072701.
6. ^ GSI Proposal EAWeb (see U248)
7. ^ see slide 11 in Future Plan of the Experimental Program on Synthesizing the Heaviest Element at RIKEN
8. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2006). "α decay half-lives of new superheavy elements". Phys. Rev. C 73: 014612. doi:10.1103/PhysRevC.73.014612.
9. ^ C. Samanta, P. Roy Chowdhury and D.N. Basu (2007). "Predictions of alpha decay half lives of heavy and superheavy elements". Nucl. Phys. A 789: 142–154. doi:10.1016/j.nuclphysa.2007.04.001.
10. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2008). "Search for long lived heaviest nuclei beyond the valley of stability". Phys. Rev. C 77: 044603. doi:10.1103/PhysRevC.77.044603.
11. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2008). "Nuclear half-lives for α-radioactivity of elements with 100 ≤ Z ≤ 130". At. Data & Nucl. Data Tables 94: 781–806. doi:10.1016/j.adt.2008.01.003.
12. ^ a b Feng, Zhao-Qing (2007). "Formation of superheavy nuclei in cold fusion reactions". Physical Review C 76: 044606. doi:10.1103/PhysRevC.76.044606. http://arxiv.org/pdf/0707.2588.
13. ^ a b c d e f Zagebraev, V; Greiner, W (2008). "Synthesis of superheavy nuclei: A search for new production reactions". Physical Review C 78: 034610. doi:10.1103/PhysRevC.78.034610. http://arxiv.org/pdf/0807.2537v1.
14. ^ a b Feng, Z (2009). "Production of heavy and superheavy nuclei in massive fusion reactions". Nuclear Physics A 816: 33. doi:10.1016/j.nuclphysa.2008.11.003. http://arxiv.org/pdf/0803.1117.
15. ^ a b c Nasirov, A. K. (2009). "Quasifission and fusion-fission in reactions with massive nuclei: Comparison of reactions leading to the Z=120 element". Physical Review C 79: 024606. doi:10.1103/PhysRevC.79.024606. http://arxiv.org/pdf/0812.4410.