Isotopes of ununhexium
Ununhexium (Uuh) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 293Uuh in 2000. There are four known radioisotopes from 290Uuh to 293Uuh. The longest-lived isotope is 293Uuh with a half-life of 53 ms.
Contents
|
[edit] Table
| nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s) | daughter isotope(s) |
nuclear spin |
|---|---|---|---|---|---|---|---|
| 290Uuh[n 1] | 116 | 174 | 290.19859(91)# | 15(+26-6) ms | α | 286Uuq | 0+ |
| 291Uuh | 116 | 175 | 291.20001(91)# | 6.3(+116-25) ms | α | 287Uuq | |
| 292Uuh | 116 | 176 | 292.19979(92)# | 18.0(+16-6) ms | α | 288Uuq | 0+ |
| 293Uuh | 116 | 177 | unknown | 53(+62-19) ms | α | 289Uuq |
- ^ Not directly synthesized, created as decay product of 294Uuo
[edit] Notes
- Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
- Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
[edit] Isotopes and nuclear properties
[edit] Nucleosynthesis
[edit] Target-projectile combinations leading to Z=116 compound nuclei
The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 116.
| Target | Projectile | CN | Attempt result |
|---|---|---|---|
| 208Pb | 82Se | 290Uuh | Failure to date |
| 232Th | 58Fe | 290Uuh | Reaction yet to be attempted |
| 238U | 54Cr | 292Uuh | Failure to date |
| 244Pu | 50Ti | 294Uuh | Reaction yet to be attempted |
| 248Cm | 48Ca | 296Uuh | Successful reaction |
| 246Cm | 48Ca | 294Uuh | Reaction yet to be attempted |
| 245Cm | 48Ca | 293Uuh | Successful reaction |
| 249Cf | 40Ar | 289Uuh | Reaction yet to be attempted |
[edit] Cold fusion
[edit] 208Pb(82Se,xn)290−xUuh
In 1998, the team at GSI attempted the synthesis of 290Uuh as a radiative capture (x=0) product. No atoms were detected providing a cross section limit of 4.8 pb.
[edit] Hot fusion
This section deals with the synthesis of nuclei of ununhexium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40–50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3–5 neutrons. Fusion reactions utilizing 48Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30–35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.
[edit] 238U(54Cr,xn)292−xUuh
There are sketchy indications that this reaction was attempted by the team at GSI in 2006. There are no published results on the outcome, presumably indicating that no atoms were detected. This is expected from a study of the systematics of cross sections for 238U targets.[1]
[edit] 248Cm(48Ca,xn)296−xUuh (x=3,4)
The first attempt to synthesise ununhexium was performed in 1977 by Ken Hulet and his team at the Lawrence Livermore National Laboratory (LLNL). They were unable to detect any atoms of ununhexium.[2]Yuri Oganessian and his team at the Flerov Laboratory of Nuclear Reactions (FLNR) subsequently attempted the reaction in 1978 and were met by failure. In 1985, a joint experiment between Berkeley and Peter Armbruster's team at GSI, the result was again negative with a calculated cross-section limit of 10–100 pb.[3]
In 2000, Russian scientists at Dubna finally succeeded in detecting a single atom of ununhexium, assigned to the isotope 292Uuh.[4] In 2001, they repeated the reaction and formed a further 2 atoms in a confirmation of their discovery experiment. A third atom was tentatively assigned to293Uuh on the basis of a missed parental alpha decay.[5] In April 2004, the team ran the experiment again at higher energy and were able to detect a new decay chain, assigned to 292Uuh. On this basis, the original data were reassigned to 293Uuh. The tentative chain is therefore possibly associated with a rare decay branch of this isotope. In this reaction, 2 further atoms of 293Uuh were detected.[6]
In an experiment run at the GSI between June-July 2010, scientists detected six atoms of unuhexium; two atoms of 293116 and four atoms of 292116. They were able to confirm both the decay data and cross sections for the fusion reaction.
[edit] 245Cm(48Ca,xn)293−x116 (x=2,3)
In order to assist in the assignment of isotope mass numbers for ununhexium, in March–May 2003 the Dubna team bombarded a 245Cm target with 48Ca ions. They were able to observe two new isotopes, assigned to 291Uuh and 290Uuh.[7]This experiment was successfully repeated in Feb–March 2005 where 10 atoms were created with identical decay data to those reported in the 2003 experiment.[8]
[edit] As a decay product
Ununhexium has also been observed in the decay of ununoctium. In October 2006 it was announced that 3 atoms of ununoctium had been detected by the bombardment ofcalifornium-249 with calcium-48 ions, which then rapidly decayed into ununhexium.[8]
The observation of 290Uuh allowed the assignment of the product to 294Uuo and proved the synthesis of ununoctium.
[edit] Fission of compound nuclei with Z=116
Several experiments have been performed between 2000–2006 at the Flerov laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nuclei 296,294,290Uuh. Four nuclear reactions have been used, namely 248Cm+48Ca, 246Ca+48Ca,244Pu+50Ti and 232Th+58Fe. 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 and58Fe projectiles, indicating a possible future use of 58Fe projectiles in superheavy element formation.In addition, in comparative experiments synthesizing 294Uuh using 48Ca and 50Ti projectiles, the yield from fusion-fission was ~3x less for 50Ti, also suggesting a future use in SHE production[9]
[edit] Retracted isotopes
[edit] 289Uuh
In 1999, researchers at Lawrence Berkeley National Laboratory announced the synthesis of 293Uuo (see ununoctium), in a paper published in Physical Review Letters.[10]The claimed isotope 289Uuh decayed by 11.63 MeV alpha emission with a half-life of 0.64 ms. The following year, they published a retraction after other researchers were unable to duplicate the results.[11] In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by the principal author Victor Ninov. As such, this isotope of ununhexium is currently unknown.
[edit] Chronology of isotope discovery
| Isotope | Year discovered | Discovery reaction |
|---|---|---|
| 290Uuh | 2002 | 249Cf(48Ca,3n)[12] |
| 291Uuh | 2003 | 245Cm(48Ca,2n)[7] |
| 292Uuh | 2004 | 248Cm(48Ca,4n)[6] |
| 293Uuh | 2000 | 248Cm(48Ca,3n)[4] |
[edit] Yields of isotopes
[edit] Hot fusion
The table below provides cross-sections and excitation energies for hot fusion reactions producing ununhexium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.
| Projectile | Target | CN | 2n | 3n | 4n | 5n |
|---|---|---|---|---|---|---|
| 48Ca | 248Cm | 296Uuh | 1.1 pb, 38.9 MeV[6] | 3.3 pb, 38.9 MeV [6] | ||
| 48Ca | 245Cm | 293Uuh | 0.9 pb, 33.0 MeV[7] | 3.7 pb, 37.9 MeV [7] |
[edit] Theoretical calculations
[edit] Decay characteristics
Theoretical calculation in a quantum tunneling model supports the experimental data relating to the synthesis of 293,292Uuh.[13][14]
[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 |
|---|---|---|---|---|---|---|
| 208Pb | 82Se | 290Uuh | 1n (289Uuh) | 0.1 pb | DNS | [15] |
| 208Pb | 79Se | 287Uuh | 1n (286Uuh) | 0.5 pb | DNS | [15] |
| 238U | 54Cr | 292Uuh | 2n (290Uuh) | 0.1 pb | DNS | [16] |
| 250Cm | 48Ca | 298Uuh | 4n (294Uuh) | 5 pb | DNS | [16] |
| 248Cm | 48Ca | 296Uuh | 4n (292Uuh) | 2 pb | DNS | [16] |
| 247Cm | 48Ca | 295Uuh | 3n (292Uuh) | 3 pb | DNS | [16] |
| 245Cm | 48Ca | 293Uuh | 3n (290Uuh) | 1.5 pb | DNS | [16] |
[edit] References
- ^ "List of experiments 2000–2006"
- ^ Hulet, E. K.; Lougheed, R.; Wild, J.; Landrum, J.; Stevenson, P.; Ghiorso, A.; Nitschke, J.; Otto, R. et al (1977). "Search for Superheavy Elements in the Bombardment of 248Cm with48Ca". Physical Review Letters 39 (7): 385. Bibcode 1977PhRvL..39..385H. doi:10.1103/PhysRevLett.39.385.
- ^ Armbruster, P.; Agarwal, YK; Brüchle, W; Brügger, M; Dufour, JP; Gaggeler, H; Hessberger, FP; Hofmann, S et al (1985). "Attempts to Produce Superheavy Elements by Fusion of 48Ca with 248Cm in the Bombarding Energy Range of 4.5–5.2 MeV/u". Physical Review Letters 54 (5): 406–409. Bibcode 1985PhRvL..54..406A. doi:10.1103/PhysRevLett.54.406. PMID 10031507.
- ^ a b Oganessian, Yu. Ts. (2000). "Observation of the decay of ^{292}116". Physical Review C 63: 011301. Bibcode 2001PhRvC..63a1301O. doi:10.1103/PhysRevC.63.011301.
- ^ "Confirmed results of the 248Cm(48Ca,4n)292116 experiment", Patin et al., LLNL report (2003). Retrieved 2008-03-03
- ^ a b c d Oganessian, Yu. Ts. (2004). "Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactions ^{233,238}U, ^{242}Pu, and ^{248}Cm+^{48}Ca". Physical Review C 70: 064609. Bibcode 2004PhRvC..70f4609O. doi:10.1103/PhysRevC.70.064609.
- ^ a b c d Oganessian, Yu. Ts.; Utyonkov, V.; Lobanov, Yu.; Abdullin, F.; Polyakov, A.; Shirokovsky, I.; Tsyganov, Yu.; Gulbekian, G. et al (2004). "Measurements of cross sections for the fusion-evaporation reactions244Pu(48Ca,xn)292−x114 and 245Cm(48Ca,xn)293−x116". Physical Review C 69 (5): 054607. Bibcode 2004PhRvC..69e4607O. doi:10.1103/PhysRevC.69.054607.
- ^ a b Synthesis of the isotopes of elements 118 and 116 in the 249Cf and 245Cm+48Ca fusion reactions.
- ^ see Flerov lab annual reports 2000–2006
- ^ Ninov, V.; et al. (1999). "Observation of Superheavy Nuclei Produced in the Reaction of86Kr with 208Pb". Physical Review Letters 83 (6): 1104. Bibcode 1999PhRvL..83.1104N. doi:10.1103/PhysRevLett.83.1104.
- ^ Ninov, V. (2002). "Editorial Note: Observation of Superheavy Nuclei Produced in the Reaction of ^{86}Kr with ^{208}Pb [Phys. Rev. Lett. 83, 1104 (1999)]". Physical Review Letters 89: 039901. Bibcode 2002PhRvL..89c9901N. doi:10.1103/PhysRevLett.89.039901.
- ^ see ununoctium
- ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2006). "α decay half-lives of new superheavy elements". Phys. Rev. C 73: 014612. arXiv:nucl-th/0507054. Bibcode 2006PhRvC..73a4612C. doi:10.1103/PhysRevC.73.014612.
- ^ 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. arXiv:nucl-th/0703086. Bibcode 2007NuPhA.789..142S. doi:10.1016/j.nuclphysa.2007.04.001.
- ^ a b Feng, Zhao-Qing; Jin, Gen-Ming; Li, Jun-Qing; Scheid, Werner (2007). "Formation of superheavy nuclei in cold fusion reactions". Physical Review C 76 (4): 044606. arXiv:0707.2588. Bibcode 2007PhRvC..76d4606F. doi:10.1103/PhysRevC.76.044606.
- ^ a b c d e Feng, Z; Jin, G; Li, J; Scheid, W (2009). "Production of heavy and superheavy nuclei in massive fusion reactions". Nuclear Physics A 816: 33. arXiv:0803.1117. Bibcode 2009NuPhA.816...33F. doi:10.1016/j.nuclphysa.2008.11.003.
- Isotope masses from:
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- Isotopic compositions and standard atomic masses from:
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683. http://www.iupac.org/publications/pac/75/6/0683/pdf/.
- M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry 78 (11): 2051–2066. doi:10.1351/pac200678112051. http://iupac.org/publications/pac/78/11/2051/pdf/. Lay summary.
- Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/. Retrieved September 2005.
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859.
| Isotopes of ununpentium | Isotopes of ununhexium | Isotopes of ununseptium |
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