Ununseptium

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ununhexium ← Ununseptium → ununoctium
At
↑
Uus
↓
(Uhs)
Appearance
Unknown
General properties
Name, symbol, number Ununseptium, Uus, 117
Category notes Unknown
Group, period, block 17, 7, p
Standard atomic weight Unknown g·mol−1
Electron configuration Unknown
Electrons per shell 2,8,18,32,32,18,7
(predicted) (Image)
Physical properties
Atomic properties
Miscellanea
CAS registry number 87658-56-8
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Ununseptium (pronounced /uːnuːnˈsɛptiəm/ ( listen)[1] oon-oon-SEP-tee-əm) is the temporary name of an undiscovered chemical element with the temporary symbol Uus and atomic number 117. It is the only missing element in period 7 of the periodic table. Since it is placed below the halogens it may share qualities similar to astatine or iodine. The first attempt to synthesize this element is currently underway at the Flerov Laboratory of Nuclear Reactions in Dubna, Russia.

Contents

[edit] History

[edit] Naming

The element with Z=117 is historically known as eka-astatine (see 'eka' terminology). The name ununseptium is a systematic element name, used as a placeholder until the element is discovered, the discovery is acknowledged by the IUPAC, and the IUPAC decides on a name. Usually, the name suggested by the discoverer(s) is chosen.

According to current guidelines from IUPAC, the ultimate name for all new elements should end in "-ium", which means the name for element 117 may end in -ium, not -ine, even if ununseptium turns out to be a halogen.[2]

[edit] Current experiments

The team at the Flerov laboratory of nuclear reactions has begun an experiment to synthesize element 117 using the reaction[3][4]

4820Ca + 24997Bk → 297117Uus* → 294117Uus + 310n.

The expected cross-section is of the order of ~2 pb. The expected evaporation residues, 293117 and 294117, are predicted to decay via relatively long decay chains as far as isotopes of dubnium or lawrencium.

Calculated decay chains from the parent nuclei 293Uus and 294 Uus[5]

Calculated excitation function for the production of the compound nucleus 297117 from the reaction 249Bk( 48Ca,xn) [5]

[edit] Future experiments

The team at the GSI in Darmstadt, recently acknowledged as the discoverers of element 112 (see ununbium) have begun experiments aiming towards a synthesis of element 117. The GSI have indicated that if they are unable to acquire any 249Bk from the United States, which is likely given the situation regarding the attempt in Russia, they will study the reaction 244Pu(51V,xn) instead, or possibly 243Am(50Ti,xn).[6]

[edit] Isotopes and nuclear properties

[edit] Nucleosynthesis

[edit] Target-projectile combinations leading to Z=117 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=117.

Target Projectile CN Attempt result
208Pb 81Br 289117 Reaction yet to be attempted
232Th 59Co 291117 Reaction yet to be attempted
238U 55Mn 293117 Reaction yet to be attempted
237Np 54Cr 291117 Reaction yet to be attempted
244Pu 51V 295117 Reaction yet to be attempted
243Am 50Ti 293117 Reaction yet to be attempted
248Cm 45Sc 293117 Reaction yet to be attempted
249Bk 48Ca 297117 In progress
249Cf 41K 290117 Reaction yet to be attempted

[edit] Theoretical calculations

[edit] Evaporation residue 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.

DNS = Di-nuclear system; σ = cross section

Target Projectile CN Channel (product) σmax Model Ref
209Bi 82Se 291117 1n (290117) 15 fb DNS [7]
209Bi 79Se 288117 1n (287117) 0.2 pb DNS [7]
232Th 59Co 291117 2n (289117) 0.1 pb DNS [7]
238U 55Mn 293117 2-3n (291,290117) 70 fb DNS [7]
244Pu 51V 295117 3n (292117) 0.6 pb DNS [7]
248Cm 45Sc 293117 4n (289117) 2.9 pb DNS [7]
246Cm 45Sc 291117 4n (287117) 1 pb DNS [7]
249Bk 48Ca 297117 3n (294117) 2.1 pb ; 3 pb DNS [7][8]
247Bk 48Ca 295117 3n (292117) 0.8, 0.9 pb DNS [8][7]

[edit] Decay characteristics

Theoretical calculations in a quantum tunneling model with mass estimates from a macroscopic-microscopic model predict the alpha-decay half-lives of isotopes of the element 117 (namely, 289-303117) to be around 0.1–40 ms.[9][10][11]

[edit] Chemical properties

[edit] Predicted chemical properties

Certain chemical properties, such as bond lengths, are predicted to differ from what one would expect based on periodic trends from the lighter halogens (because of relativistic effects).[12]

[edit] References

  1. ^ J. Chatt (1979). "Recommendations for the Naming of Elements of Atomic Numbers Greater than 100". Pure Appl. Chem. 51: 381–384. doi:10.1351/pac197951020381. 
  2. ^ Koppenol, W. H. (2002). "Naming of new elements(IUPAC Recommendations 2002)". Pure and Applied Chemistry 74: 787. doi:10.1351/pac200274050787. http://media.iupac.org/publications/pac/2002/pdf/7405x0787.pdf. 
  3. ^ New chemical element to be synthesized in Russia
  4. ^ Flerov Lab.
  5. ^ a b sagaidak. "Experiment setting on synthesis of superheavy nuclei in fusion-evaporation reactions. Preparation to synthesis of new element with Z=117". http://159.93.28.88/linkc/education/SHE_Sagaidak.pdf. Retrieved 2009-07-07. 
  6. ^ Toward element 117
  7. ^ a b c d e f g h i Zhao-Qing, Feng (2007). "Possible Way to Synthesize Superheavy Element Z = 117". Chinese Physics Letters 24: 2551. doi:10.1088/0256-307X/24/9/024. http://arxiv.org/pdf/0708.0159. 
  8. ^ 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. 
  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. 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. ^ Trond Saue. "Principles and Applications of Relativistic Molecular Calculations". http://dirac.chem.sdu.dk/thesis/96.saue_phd.pdf. , page 76
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