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Unbibium (pronounced /uːnˈbɪbiəm/), 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[1] 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:

\,^{238}_{92}\mathrm{U} + \,^{66}_{30}\mathrm{Zn} \to \,^{304}_{122}\mathrm{Ubb} ^{*} \to \ \mbox{no atoms}.

No atoms were detected and a yield limit of 5 mb (5,000,000 pb)[dubious – discuss] was measured. Current results (see ununquadium) have shown that the sensitivity of this experiment was too low by at least 6 orders of magnitude.

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

\,^{238}_{92}\mathrm{U} + \,^{70}_{30}\mathrm{Zn} \to \,^{308}_{122}\mathrm{Ubb} ^{*} \to \ \mbox{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.
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.[2]
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.

Target Projectile CN Attempt result
208Pb 94Zr 302Ubb Reaction yet to be attempted
232Th 74Ge 306Ubb Reaction yet to be attempted
238U 70Zn 308Ubb Failure to date
238U 66Zn 304Ubb Failure to date
244Pu 64Ni 308Ubb Reaction yet to be attempted
248Cm 58Fe 306Ubb Reaction yet to be attempted
249Cf 54Cr 303Ubb Reaction yet to be attempted


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.[1] 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.[3].

A criticism of the technique, previously used in purportedly identifying lighter thorium isotopes by mass spectrometry,[4][5] was published in Physical Review C in 2008.[6] A rebuttal by the Marinov group was published in Physical Review C after the published comment.[7]

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.[8] 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.
See also

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

References

1. ^ a b Marinov, A.; Rodushkin, I.; Kolb, D.; Pape, A.; Kashiv, Y.; Brandt, R.; Gentry, R. V.; Miller, H. W. (2008). "Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th". ArXiv.org. http://arxiv.org/abs/0804.3869. Retrieved 2008-04-28.
2. ^ see Flerov lab annual reports 2000–2004 inclusive http://www1.jinr.ru/Reports/Reports_eng_arh.html
3. ^ Royal Society of Chemistry, "Heaviest element claim criticised", Chemical World.
4. ^ A. Marinov; I. Rodushkin; Y. Kashiv; L. Halicz; I. Segal; A. Pape; R. V. Gentry; H. W. Miller; D. Kolb; R. Brandt (2007). "Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes". Phys. Rev. C 76: 021303(R). doi:10.1103/PhysRevC.76.021303.
5. ^ Marinov, A.; Rodushkin, I.; Kashiv, Y.; Halicz, L.; Segal, I.; Pape, A.; Gentry, R.; Miller, H. et al. (2007). "Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes". Physical Review C 76: 021303. doi:10.1103/PhysRevC.76.021303. http://arxiv.org/ftp/nucl-ex/papers/0605/0605008.pdf.
6. ^ R. C. Barber; J. R. De Laeter (2009). "Comment on “Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes”". Phys. Rev. C 79: 049801. doi:10.1103/PhysRevC.79.049801.
7. ^ A. Marinov; I. Rodushkin; Y. Kashiv; L. Halicz; I. Segal; A. Pape; R. V. Gentry; H. W. Miller; D. Kolb; R. Brandt (2009). "Reply to “Comment on `Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes'”". Phys. Rev. C 79: 049802. doi:10.1103/PhysRevC.79.049802.
8. ^ J. Lachner; I. Dillmann; T. Faestermann; G. Korschinek; M. Poutivtsev; G. Rugel (2008). "Search for long-lived isomeric states in neutron-deficient thorium isotopes". Phys. Rev. C 78: 064313. doi:10.1103/PhysRevC.78.064313.

External links

* Chemistry-Blog: Independent analysis of Marinov’s 122 claim
* Marinov's Site
.

Chemistry Encyclopedia

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