Isotopes of roentgenium


is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic 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 nihonium, moscovium, and tennessine, and possibly copernicium, flerovium, and livermorium. There are 7 known radioisotopes from 272Rg to 282Rg. The longest-lived isotope is 282Rg with a half-life of 2.1 minutes, although the unconfirmed 283Rg and 286Rg may have longer half-lives of about 5.1 minutes and 10.7 minutes respectively.

List of isotopes

Isotopes and nuclear properties

Nucleosynthesis

s 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.
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, giving rise to compound nuclei at high excitation energy that may either fission or evaporate several neutrons. In cold fusion reactions, the produced fused nuclei have a relatively low excitation energy, 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. The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions.
The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=111.
TargetProjectileCNAttempt result
205Tl70Zn275Rg
208Pb65Cu273Rg
209Bi64Ni273Rg
231Pa48Ca279Rg
238U41K279Rg
244Pu37Cl281Rg
248Cm31P279Rg
250Cm31P281Rg

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. A further 3 atoms were synthesized in 2002. The discovery of roentgenium was confirmed in 2003 when a team at RIKEN measured the decays of 14 atoms of 272Rg.
The same roentgenium isotope was also observed by an American team at the Lawrence Berkeley National Laboratory from the reaction:
This reaction was conducted as part of their study of projectiles with odd atomic number in cold fusion reactions.
The 205Tl274Rg reaction was tried by the RIKEN team in 2004 and repeated in 2010 in an attempt to secure the discovery of its parent 278Nh:
Due to the weakness of the thallium target, they were unable to detect any atoms of 274Rg.

As decay product


Evaporation residueObserved roentgenium isotope
294Lv, 290Fl, 290Nh ?286Rg ?
299Ubn, 295Og, 291Lv, 287Fl, 287Nh ?283Rg ?
294Ts, 290Mc, 286Nh282Rg
293Ts, 289Mc, 285Nh281Rg
288Mc, 284Nh280Rg
287Mc, 283Nh279Rg
282Nh278Rg
278Nh274Rg


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 nihonium. Nihonium currently has seven known isotopes; all of them undergo alpha decays to become roentgenium nuclei, with mass numbers between 274 and 286. Parent nihonium nuclei can be themselves decay products of flerovium, moscovium, livermorium, tennessine, and oganesson or unbinilium. To date, no other elements have been known to decay to roentgenium. For example, in January 2010, the Dubna team identified roentgenium-281 as a final product in the decay of tennessine via an alpha decay sequence:

Nuclear isomerism

;274Rg
Two atoms of 274Rg have been observed in the decay chain of 278Nh. 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.
;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 while 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.

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.
ProjectileTargetCN1n2n3n
64Ni209Bi273Rg3.5 pb, 12.5 MeV--
65Cu208Pb273Rg1.7 pb, 13.2 MeV--

Theoretical calculations

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
TargetProjectileCNChannel σmaxModelRef
238U41K279Rg4n 0.21 pbDNS
244Pu37Cl281Rg4n 0.33 pbDNS
248Cm31P279Rg4n 1.85 pbDNS
250Cm31P281Rg4n 0.41 pbDNS