Isotopes of roentgenium

Roentgenium (Rg) 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 ²⁷²Rg in 1994, which is also the only directly synthesized isotope, all others are decay products of ununtrium, ununpentium, and ununseptium. There are 7 known radioisotopes from ²⁷²Rg to ²⁸²Rg. The longest-lived isotope is ²⁸¹Rg with a half-life of 26 seconds.

Table

1. ↑ Abbreviations:
   SF: Spontaneous fission
2. ↑ Not directly synthesized, occurs as a decay product of ²⁷⁸Uut
3. ↑ Not directly synthesized, occurs as a decay product of ²⁸²Uut
4. ↑ Not directly synthesized, occurs in decay chain of ²⁸⁷Uup
5. ↑ Not directly synthesized, occurs in decay chain of ²⁸⁸Uup
6. ↑ Not directly synthesized, occurs in decay chain of ²⁹³Uus
7. ↑ Not directly synthesized, occurs in decay chain of ²⁹⁴Uus

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.

Isotopes and nuclear properties

Nucleosynthesis

Super-heavy elements such as roentgenium are produced by bombarding lighter elements in particle accelerators that induce fusion reactions. Whereas the lightest isotope of roentgenium, roentgenium-272, can be synthesized directly this way, all the heavier roentgenium isotopes have only been observed as decay products of elements with higher atomic numbers.^[3]

Depending on the energies involved, fusion reactions can be categorized as "hot" or "cold". In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets (actinides), giving rise to compound nuclei at high excitation energy (~40–50 MeV) that may either fission or evaporate several (3 to 5) neutrons.^[4] In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to the ground state, they require emission of only one or two neutrons, and thus, allows for the generation of more neutron-rich products.^[3] The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion).^[5]

Cold fusion

Before the first successful synthesis of roentgenium in 1994 by the GSI team, a team at the Joint Institute for Nuclear Research in Dubna, Russia, also tried to synthesize roentgenium by bombarding bismuth-209 with nickel-64 in 1986. No roentgenium atoms were identified. After an upgrade of their facilities, the team at GSI successfully detected 3 atoms of ²⁷²Rg in their discovery experiment.^[6] A further 3 atoms were synthesized in 2002.^[7] The discovery of roentgenium was confirmed in 2003 when a team at RIKEN measured the decays of 14 atoms of ²⁷²Rg.^[8]

The same roentgenium isotope was also observed by an American team at the Lawrence Berkeley National Laboratory (LBNL) from the reaction:

208
82Pb + 65
29Cu → 272
111Rg + n

This reaction was conducted as part of their study of projectiles with odd atomic number in cold fusion reactions.^[9]

As decay product

All the isotopes of roentgenium except roentgenium-272 have been detected only in the decay chains of elements with a higher atomic number, such as ununtrium. Ununtrium currently has six known isotopes; all of them undergo alpha decays to become roentgenium nuclei, with mass numbers between 274 and 282. Parent ununtrium nuclei can be themselves decay products of ununpentium or ununseptium. To date, no other elements have been known to decay to roentgenium.^[12] For example, in January 2010, the Dubna team (JINR) identified roentgenium-281 as a final product in the decay of ununseptium via an alpha decay sequence:^[1]

293
117Uus → 289
115Uup + 4
2He

289
115Uup → 285
113Uut + 4
2He

285
113Uut → 281
111Rg + 4
2He

Nuclear isomerism

²⁷⁴Rg

Two atoms of ²⁷⁴Rg have been observed in the decay chain of ²⁷⁸Uut. They decay by alpha emission, emitting alpha particles with different energies, and have different lifetimes. In addition, the two entire decay chains appear to be different. This suggests the presence of two nuclear isomers but further research is required.^[11]

²⁷²Rg

Four alpha particles emitted from ²⁷²Rg with energies of 11.37, 11.03, 10.82, and 10.40 MeV have been detected. The GSI measured ²⁷²Rg to have a half-life of 1.6 ms whilst recent data from RIKEN have given a half-life of 3.8 ms. The conflicting data may be due to nuclear isomers but the current data are insufficient to come to any firm assignments.^[6][8]

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing roentgenium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

References

• Isotope masses from:
  • M. Wang, G. Audi, A.H. Wapstra, F.G. Kondev, M. MacCormick, X. Xu, et al. (2012). "The AME2012 atomic mass evaluation (II). Tables, graphs and references.". Chinese Physics C, 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003. 
  • 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. 
• 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. 
  • 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. 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. 
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. 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 978-0-8493-0485-9. 
  • Yu. Ts. Oganessian (2007). "Heaviest nuclei from ⁴⁸Ca-induced reactions". Journal of Physics G 34 (4): R165–R242. Bibcode:2007JPhG...34..165O. doi:10.1088/0954-3899/34/4/R01.