Isotopes of meitnerium

Meitnerium (Mt) is a synthetic element, and thus a standard atomic mass cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was ²⁶⁶Mt in 1982 (this is also the only isotope directly synthesized, all other isotopes are 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.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin
	excitation energy
^266Mt	109	157	266.13737(33)#	1.2(4) ms	α	^262Bh
^268Mt[n 1]	109	159	268.13865(25)#	21(+8−5) ms	α	^264Bh	5+#,6+#
^268mMt[n 2]	0+X keV			0.07(+10−3) s	α	^264Bh
^270Mt[n 3]	109	161	270.14033(18)#	0.57 s	α	^266Bh
^270mMt[n 2]				1.1 s?	α	^266Bh
^274Mt[n 4]	109	165	274.14725(38)#	0.45 s	α	^270Bh
^275Mt[n 5]	109	166	275.14882(50)#	9.7(+460−44) ms	α	^271Bh
^276Mt[n 6]	109	167	276.15159(59)#	0.72(+87-25) s	α	^272Bh
^277Mt[n 7]	109	168	277.15327(82)#	~5 ms[1][2]	SF	(various)
^278Mt[n 8]	109	169	278.15631(68)#	7.6 s[3]	α	^274Bh

1. Not directly synthesized, occurs as decay product of ²⁷²Rg
2. This isomer is unconfirmed
3. Not directly synthesized, occurs in decay chain of ²⁷⁸Uut
4. Not directly synthesized, occurs in decay chain of ²⁸²Uut
5. Not directly synthesized, occurs in decay chain of ²⁸⁷Uup
6. Not directly synthesized, occurs in decay chain of ²⁸⁸Uup
7. Not directly synthesized, occurs in decay chain of ²⁹³Uus
8. 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 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.^[4]

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.^[5] 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.^[4] 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).^[6]

Cold fusion

After the first successful synthesis of meitnerium in 1982 by the GSI team,^[7] 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.^[8][9]

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.^[10]

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.^[11] 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.^[12] 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.^[11]

Decay products

List of meitnerium isotopes observed by decay

Evaporation residue	Observed meitnerium isotope
^294Uus, ^290Uup, ^286Uut, ^282Rg	^278Mt[13]
^293Uus, ^289Uup, ^285Uut, ^281Rg	^277Mt[1]
^288Uup, ^284Uut, ^280Rg	^276Mt[14]
^287Uup, ^283Uut, ^279Rg	^275Mt[14]
^282Uut, ^278Rg	^274Mt[14]
^278Uut, ^274Rg	^270Mt[15]
^272Rg	^268Mt[16]

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 ununtrium, ununpentium, or ununseptium. To date, no other elements have been known to decay to meitnerium.^[17] For example, in January 2010, the Dubna team (JINR) identified meitnerium-278 as a product in the decay of ununseptium via an alpha decay sequence:^[13]

294
117Uus → 290
115Uup + 4
2He

290
115Uup → 286
113Uut + 4
2He

286
113Uut → 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 ²⁷⁸Uut. 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.^[15]

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.^[16]

Nuclear isomerism

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 an 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.

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.

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

Target	Projectile	CN	Channel (product)	σmax	Model	Ref
^243Am	^30Si	^273Mt	3n (^270Mt)	22 pb	HIVAP	[18]
^243Am	^28Si	^271Mt	4n (^267Mt)	3 pb	HIVAP	[18]
^249Bk	^26Mg	^275Mt	4n (^271Mt)	9.5 pb	HIVAP	[18]
^254Es	^22Ne	^276Mt	4n (^272Mt)	8 pb	HIVAP	[18]
^254Es	^20Ne	^274Mt	4-5n (^270,269Mt)	3 pb	HIVAP	[18]

References

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12. Haire, Richard G. (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer Science+Business Media. ISBN 1-4020-3555-1.
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14. Oganessian, Yu. Ts.; Penionzhkevich, Yu. E.; Cherepanov, E. A. (2007). "AIP Conference Proceedings" 912: 235. doi:10.1063/1.2746600. |chapter= ignored (help)
15. Morita, 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.
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• Isotope masses from:
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• Isotopic compositions and standard atomic masses from:
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• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
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