Meitnerium (109Mt) 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 266Mt in 1982, and this is also the only isotope directly synthesized; all other isotopes are only known as
decay products of heavier
elements. There are eight known isotopes, from 266Mt to 278Mt. There may also be two
isomers. The longest-lived of the known isotopes is 278Mt with a
half-life of 8 seconds. The unconfirmed heavier 282Mt appears to have an even longer half-life of 67 seconds.
^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
^( ) spin value – Indicates spin with weak assignment arguments.
^# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
^Not directly synthesized, occurs as
decay product of 272Rg
^Not directly synthesized, occurs in
decay chain of 278Nh
^Not directly synthesized, occurs in decay chain of 282Nh
^Not directly synthesized, occurs in decay chain of 287Mc
^Not directly synthesized, occurs in decay chain of 288Mc
^Not directly synthesized, occurs in decay chain of 293Ts
^Not directly synthesized, occurs in decay chain of 294Ts
^Not directly synthesized, occurs in decay chain of 290Fl and 294Lv; unconfirmed
Isotopes and nuclear properties
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.[5]
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.[6] 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.[5] 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).[7]
The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with Z = 109.
Target
Projectile
CN
Attempt result
208Pb
59Co
267Mt
Successful reaction
209Bi
58Fe
267Mt
Successful reaction
227Ac
48Ca
275Mt
Reaction yet to be attempted
238U
37Cl
275Mt
Failure to date
244Pu
31P
275Mt
Reaction yet to be attempted
248Cm
27Al
275Mt
Reaction yet to be attempted
250Cm
27Al
277Mt
Reaction yet to be attempted
249Bk
26Mg
275Mt
Reaction yet to be attempted
254Es
22Ne
276Mt
Failure to date
Cold fusion
After the first successful synthesis of meitnerium in 1982 by the
GSI team,[8] 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.[9][10]
The same meitnerium isotope was also observed by the Russian team at Dubna in 1985 from the reaction:
208 82Pb + 59 27Co → 266 109Mt + n
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.[11]
Hot fusion
In 2002–2003, the team at LBNL attempted to generate the isotope 271Mt to study its chemical properties by bombarding
uranium-238 with
chlorine-37, but without success.[12] 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.[13] Other potentially longer-lived isotopes were unsuccessfully targeted by a team at
Lawrence Livermore National Laboratory (LLNL) in 1988 by bombarding
einsteinium-254 with
neon-22.[12]
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 eight known isotopes; all but one of them undergo alpha decays to become meitnerium nuclei, with mass numbers between 268 and 282. Parent roentgenium nuclei can be themselves decay products of
nihonium,
flerovium,
moscovium,
livermorium, or
tennessine.[18] 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:[14]
294 117Ts → 290 115Mc + 4 2He
290 115Mc → 286 113Nh + 4 2He
286 113Nh → 282 111Rg + 4 2He
282 111Rg → 278 109Mt + 4 2He
Nuclear isomerism
270Mt
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.[16]
268Mt
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.[17]
Chemical yields of isotopes
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.
Projectile
Target
CN
1n
2n
3n
58Fe
209Bi
267Mt
7.5 pb
59Co
208Pb
267Mt
2.6 pb, 14.9 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.
^Hofmann, S.; Heinz, S.; Mann, R.; Maurer, J.; Münzenberg, G.; Antalic, S.; Barth, W.; Burkhard, H. G.; Dahl, L.; Eberhardt, K.; Grzywacz, R.; Hamilton, J. H.; Henderson, R. A.; Kenneally, J. M.; Kindler, B.; Kojouharov, I.; Lang, R.; Lommel, B.; Miernik, K.; Miller, D.; Moody, K. J.; Morita, K.; Nishio, K.; Popeko, A. G.; Roberto, J. B.; Runke, J.; Rykaczewski, K. P.; Saro, S.; Scheidenberger, C.; Schött, H. J.; Shaughnessy, D. A.; Stoyer, M. A.; Thörle-Popiesch, P.; Tinschert, K.; Trautmann, N.; Uusitalo, J.; Yeremin, A. V. (2016). "Review of even element super-heavy nuclei and search for element 120". The European Physics Journal A. 2016 (52).
doi:
10.1140/epja/i2016-16180-4.
^Haire, Richard G. (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean (eds.). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands:
Springer Science+Business Media.
ISBN1-4020-3555-1.
^
abcOganessian, Yu. Ts.; Penionzhkevich, Yu. E.; Cherepanov, E. A. (2007). "Heaviest Nuclei Produced in 48Ca-induced Reactions (Synthesis and Decay Properties)". AIP Conference Proceedings. Vol. 912. pp. 235–246.
doi:
10.1063/1.2746600.
^
abMorita, Kosuke; Morimoto, Kouji; Kaji, Daiya; Akiyama, Takahiro; Goto, Sin-ichi; Haba, Hiromitsu; Ideguchi, Eiji; Kanungo, Rituparna; Katori, Kenji; Koura, Hiroyuki; Kudo, Hisaaki; Ohnishi, Tetsuya; Ozawa, Akira; Suda, Toshimi; Sueki, Keisuke; Xu, HuShan; Yamaguchi, Takayuki; Yoneda, Akira; Yoshida, Atsushi; Zhao, YuLiang (2004).
"Experiment on the Synthesis of Element 113 in the Reaction 209Bi(70Zn,n)278113". Journal of the Physical Society of Japan. 73 (10): 2593–2596.
Bibcode:
2004JPSJ...73.2593M.
doi:10.1143/JPSJ.73.2593.
^
abHofmann, S.; Ninov, V.; Heßberger, F. P.; Armbruster, P.; Folger, H.; Münzenberg, G.; Schött, H. J.; Popeko, A. G.; Yeremin, A. V.; Andreyev, A. N.; Saro, S.; Janik, R.; Leino, M. (1995).
"The new element 111"(PDF). Zeitschrift für Physik A. 350 (4): 281–282.
Bibcode:
1995ZPhyA.350..281H.
doi:
10.1007/BF01291182.
S2CID18804192. Archived from
the original(PDF) on 2014-01-16.
^Sonzogni, Alejandro.
"Interactive Chart of Nuclides". National Nuclear Data Center: Brookhaven National Laboratory. Archived from
the original on 2018-03-07. Retrieved 2008-06-06.