Unbibium

ഫലകം:Infobox unbibium Unbibium (ഫലകം:IPAc-en), also referred to as eka-thorium or element 122, is the temporary name of a currently unknown chemical element in the periodic table that has the temporary symbol Ubb and the atomic number 122.

In 2008, it was claimed to have been discovered in natural thorium samples but that claim has now been dismissed by recent repetitions of the experiment using more accurate techniques.

History

Neutron evaporation

The first attempt to synthesize unbibium was performed in 1972 by Flerov et al. at JINR, using the hot fusion reaction:

${}_{92}^{238}\mathrm{U}+{}_{30}^{66}\mathrm{Z}\mathrm{n}\to {}_{122}^{304}{\mathrm{U}\mathrm{b}\mathrm{b}}^{*}\to \text{no atoms}.$

No atoms were detected and a yield limit of 5 mb (5,000,000 pb)ഫലകം:Dubious was measured. Current results (see flerovium) have shown that the sensitivity of this experiment was too low by at least 6 orders of magnitude.ഫലകം:Citation needed

In 2000, the Gesellschaft für Schwerionenforschung performed a very similar experiment with much higher sensitivity:

${}_{92}^{238}\mathrm{U}+{}_{30}^{70}\mathrm{Z}\mathrm{n}\to {}_{122}^{308}{\mathrm{U}\mathrm{b}\mathrm{b}}^{*}\to \text{no atoms}.$

These results indicate that the synthesis of such heavier elements remains a significant challenge and further improvements of beam intensity and experimental efficiency is required. The sensitivity should be increased to 1 fb.ഫലകം:Citation needed

Compound nucleus fission

Several experiments have been performed between 2000-2004 at the Flerov laboratory of Nuclear Reactions studying the fission characteristics of the compound nucleus ³⁰⁶Ubb. Two nuclear reactions have been used, namely ²⁴⁸Cm + ⁵⁸Fe and ²⁴²Pu + 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.

Claimed discovery as a naturally occurring element

On April 24, 2008, a group led by Amnon Marinov at the Hebrew University of Jerusalem claimed to have found single atoms of unbibium in naturally occurring thorium deposits at an abundance of between 10⁻¹¹ and 10⁻¹², relative to thorium. The claim of Marinov et al. was criticized by a part of the scientific community, and Marinov says he has submitted the article to the journals Nature and Nature Physics but both turned it down without sending it for peer review.

A criticism of the technique, previously used in purportedly identifying lighter thorium isotopes by mass spectrometry, was published in Physical Review C in 2008. A rebuttal by the Marinov group was published in Physical Review C after the published comment.

A repeat of the thorium-experiment using the superior method of Accelerator Mass Spectrometry (AMS) failed to confirm the results, despite a 100-fold better sensitivity. This result throws considerable doubt on the results of the Marinov collaboration with regards to their claims of long-lived isotopes of thorium, roentgenium and unbibium.

Nucleosynthesis

Target-projectile combinations leading to Z=122 compound nuclei

The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 122.ഫലകം:Citation needed

Target	Projectile	CN	Attempt result
238U	70Zn	308Ubb	ഫലകം:No
238U	66Zn	304Ubb	ഫലകം:No
242Pu	64Ni	306Ubb	ഫലകം:No
248Cm	58Fe	306Ubb	ഫലകം:No

Chemical properties

Electronic structure

It has been predicted by Ephraim Eliav et al. that unbibium will have the electron configuration [Uuo]8s²7d¹8p¹.

Extrapolated chemical properties

Chemistry

If group reactivity is followed, unbibium should be a reactive metal, more reactive than cerium or thorium. Unbibium would most likely form the dioxide, UbbO₂, and trihalides, such as UbbF₃ and UbbCl₃. The predicted oxidation states are III and IV (and perhaps II).ഫലകം:Citation needed

See also

• Island of stability
• Systematic element name
• unbiunium–unbitrium

External links

• Chemistry-Blog: Independent analysis of Marinov’s 122 claim ഫലകം:Webarchive
• Marinov's Site