Unbinilium

ununennium ← unbinilium → unbiunium Ra ↑ Ubn ↓ Usn 120Ubn Periodic table
Appearance
General properties
Name, symbol, number	unbinilium, Ubn, 120
Pronunciation	/uːnbaɪˈnɪliəm/
Element category	alkaline earth metals
Group, period, block	2, 8, s
Standard atomic weight	unknown
Electron configuration	[Uuo] 8s2 (predicted)
Electrons per shell	2, 8, 18, 32, 32, 18, 8, 2 (predicted) (Image)
Physical properties
Atomic properties
Oxidation states	2, 4 (predicted)

Unbinilium ( /uːnbaɪˈnɪliəm/), also called eka-radium or element 120, 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 should be 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. 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.

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

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.

In June-July 2010, scientists at the GSI attempted the fusion reaction:

$\,^{248}_{96}\mathrm{Cm} + \,^{54}_{24}\mathrm{Cr} \to \,^{302}_{120}\mathrm{Ubn} ^{*}$

They were unable to detect any atoms but exact details are not currently available.

In August-October, a different team at the GSI using the TASCA facility tried the new reaction:

$\,^{249}_{98}\mathrm{Cf} + \,^{50}_{22}\mathrm{Ti} \to \,^{299}_{120}\mathrm{Ubn} ^{*}$

Results from this experiment are not yet available.

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.

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 > 10⁻¹⁸ s. 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.

Future reactions

The team at RIKEN have 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.

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.

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, which may be also the case 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.

Target	Projectile	CN	Attempt result
232Th	70Zn	302Ubn	Reaction yet to be attempted
238U	64Ni	302Ubn	Failure to date, σ < 94 fb
244Pu	58Fe	302Ubn	Failure to date, σ < 0.4 pb
248Cm	54Cr	302Ubn	Failure to date
249Cf	50Ti	299Ubn	Results currently unavailable
257Fm	48Ca	305Ubn	Reaction yet to be attempted

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

Target	Projectile	CN	Channel (product)	~σmax	Model	Ref
208Pb	88Sr	296Ubn	1n (295Ubn)	70 fb	DNS
208Pb	87Sr	295Ubn	1n (294Ubn)	80 fb	DNS
208Pb	88Sr	296Ubn	1n (295Ubn)	<0.1 fb	MD
238U	64Ni	302Ubn	3n (299Ubn)	3 fb	MD
238U	64Ni	302Ubn	2n (300Ubn)	0.5 fb	DNS
238U	64Ni	302Ubn	4n (298Ubn)	2 ab	DNS-AS
244Pu	58Fe	302Ubn	4n (298Ubn)	5 fb	MD
244Pu	58Fe	302Ubn	3n (299Ubn)	8 fb	DNS-AS
248Cm	54Cr	302Ubn	3n (299Ubn)	10 pb	DNS-AS
248Cm	54Cr	302Ubn	4n (298Ubn)	30 fb	MD
249Cf	50Ti	299Ubn	4n (295Ubn)	45 fb	MD
249Cf	50Ti	299Ubn	3n (296Ubn)	40 fb	MD
257Fm	48Ca	305Ubn	3n (302Ubn)	70 fb	DNS

See also

• Island of stability: ununquadium–unbinilium–unbihexium
• Radium