Isotopes of meitnerium

Notes

Nucleosynthesis

Super-heavy elements such as meitnerium are produced by bombarding lighter elements in particle accelerators that induce fusion reactions. Whereas the lightest isotope of meitnerium, meitnerium-266, can be synthesized directly this way, all the heavier meitnerium isotopes have only been observed as decay products of elements with higher atomic numbers.

Depending on the energies involved, the former are separated into "hot" and "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. 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. Nevertheless, the products of hot fusion tend to still have more neutrons overall. The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion).

Cold fusion

After the first successful synthesis of meitnerium in 1982 by the GSI team, a team at the Joint Institute for Nuclear Research in Dubna, Russia, also tried to observe the new element by bombarding bismuth-209 with iron-58. In 1985 they managed to identity alpha decays from the descendant isotope ²⁴⁶Cf indicating the formation of meitnerium. The observation of a further two atoms of ²⁶⁶Mt from the same reaction was reported in 1988 and of another 12 in 1997 by the German team at GSI.

The same meitnerium isotope was also observed by the Russian team at Dubna in 1985 from the reaction:

by detecting the alpha decay of the descendant ²⁴⁶Cf nuclei. In 2007, an American team at the Lawrence Berkeley National Laboratory (LBNL) confirmed the decay chain of the ²⁶⁶Mt isotope from this reaction.

Hot fusion

In 2002–2003, the team at the LBNL attempted to generate the isotope ²⁷¹Mt to study its chemical properties by bombarding uranium-238 with chlorine-37, but without success. Another possible reaction that would form this isotope would be the fusion of berkelium-249 with magnesium-26; however, the yield for this reaction is expected to be very low due to the high radioactivity of the berkelium-249 target. Other long-lived isotopes were unsuccessfully targeted by a team at Lawrence Livermore National Laboratory (LLNL) in 1988 by bombarding einsteinium-254 with neon-22.

Decay products

All the isotopes of meitnerium except meitnerium-266 have been detected only in the decay chains of elements with a higher atomic number, such as roentgenium. Roentgenium currently has seven known isotopes; all but one of them undergo alpha decays to become meitnerium nuclei, with mass numbers between 268 and 278. Parent roentgenium nuclei can be themselves decay products of nihonium, moscovium, or tennessine. To date, no other elements have been known to decay to meitnerium. For example, in January 2010, the Dubna team (JINR) identified meitnerium-278 as a product in the decay of tennessine via an alpha decay sequence:

Nuclear isomerism

Two atoms of ²⁷⁰Mt have been identified in the decay chains of ²⁷⁸Nh. The two decays have very different lifetimes and decay energies and are also produced from two apparently different isomers of ²⁷⁴Rg. The first isomer decays by emission of an alpha particle with energy 10.03 MeV and has a lifetime of 7.16 ms. The other alpha decays with a lifetime of 1.63 s; the decay energy was not measured. An assignment to specific levels is not possible with the limited data available and further research is required.

The alpha decay spectrum for ²⁶⁸Mt appears to be complicated from the results of several experiments. Alpha particles of energies 10.28, 10.22 and 10.10 MeV have been observed, emitted from ²⁶⁸Mt atoms with half-lives of 42 ms, 21 ms and 102 ms respectively. The long-lived decay must be assigned to an isomeric level. The discrepancy between the other two half-lives has yet to be resolved. An assignment to specific levels is not possible with the data available and further research is required.

270Mt

Two atoms of ²⁷⁰Mt have been identified in the decay chains of ²⁷⁸Uut. The two decays have very different lifetimes and decay energies and are also produced from two apparently different isomers in ²⁷⁴Rg. The first isomer decays by emission of a 10.03 MeV alpha particle with a lifetime 7.2 ms. The other decays by emitting an alpha particle with a lifetime of 1.63 s. An assignment to specific levels is not possible with the limited data available. Further research is required.

268Mt

The alpha decay spectrum for ²⁶⁸Mt appears to be complicated from the results of several experiments. Alpha lines of 10.28,10.22 and 10.10 MeV have been observed. Half-lives of 42 ms, 21 ms and 102 ms have been determined. The long-lived decay is associated with alpha particles of energy 10.10 MeV and must be assigned to an isomeric level. The discrepancy between the other two half-lives has yet to be resolved. An assignment to specific levels is not possible with the data available and further research is required.

Cold fusion

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

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.

HIVAP = heavy-ion vaporisation statistical-evaporation model; σ = cross section