Isotopes of meitnerium

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.

Isotopes of meitnerium (₁₀₉Mt)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 274Mt synth 0.64 s α 270Bh 276Mt synth 0.62 s α 272Bh 278Mt synth 4 s α 274Bh 282Mt synth 67 s?[2] α 278Bh

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List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life[1]	Decay mode[1]	Daughter isotope	Spin and parity[1] [n 4][n 5]
	Excitation energy
266Mt	109	157	266.137060(100)	2.0(5) ms	α	262Bh
266mMt	1140(90) keV			6(3) ms	α	262Bh
268Mt[n 6]	109	159	268.13865(25)#	23(7) ms	α	264Bh	5+#, 6+#
268mMt[n 7]	0+X keV			70+100 −30 ms	α	264Bh
270Mt[n 8]	109	161	270.14032(21)#	800(400) ms	α	266Bh
270mMt[n 7]				1.1 s?	α	266Bh
274Mt[n 9]	109	165	274.14734(40)#[3]	640+760 −230 ms[3]	α	270Bh
275Mt[n 10]	109	166	275.14897(42)#	20+13 −6 ms[3]	α	271Bh
276Mt[n 11]	109	167	276.15171(57)#	620+60 −40 ms[3]	α	272Bh
276mMt[n 11]	250(80) keV			7(3) s	α	272Bh
277Mt[n 12]	109	168	277.15353(71)#	5+9 −2 ms[4]	SF	(various)
278Mt[n 13]	109	169	278.15649(62)#	6(3) s	α	274Bh
282Mt[n 14]	109	173	282.16689(48)#	67 s?	α	278Bh
This table header & footer: view

1. ^mMt – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. ( ) spin value – Indicates spin with weak assignment arguments.
5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Not directly synthesized, occurs as decay product of ²⁷²Rg
7. This isomer is unconfirmed
8. Not directly synthesized, occurs in decay chain of ²⁷⁸Nh
9. Not directly synthesized, occurs in decay chain of ²⁸²Nh
10. Not directly synthesized, occurs in decay chain of ²⁸⁷Mc
11. Not directly synthesized, occurs in decay chain of ²⁸⁸Mc
12. Not directly synthesized, occurs in decay chain of ²⁹³Ts
13. Not directly synthesized, occurs in decay chain of ²⁹⁴Ts
14. 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
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]

Decay products

List of meitnerium isotopes observed by decay

Evaporation residue	Observed meitnerium isotope
294Lv, 290Fl, 290Nh, 286Rg ?	282Mt ?
294Ts, 290Mc, 286Nh, 282Rg	278Mt[14]
293Ts, 289Mc, 285Nh, 281Rg	277Mt[4]
288Mc, 284Nh, 280Rg	276Mt[15]
287Mc, 283Nh, 279Rg	275Mt[15]
286Mc, 282Nh, 278Rg	274Mt[15]
278Nh, 274Rg	270Mt[16]
272Rg	268Mt[17]

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.

DNS = Di-nuclear system; HIVAP = heavy-ion vaporisation statistical-evaporation model; σ = cross section

Target	Projectile	CN	Channel (product)	σmax	Model	Ref
238U	37Cl	275Mt	3n (272Mt)	13.31 pb	DNS	[19]
244Pu	31P	275Mt	3n (272Mt)	4.25 pb	DNS	[19]
243Am	30Si	273Mt	3n (270Mt)	22 pb	HIVAP	[20]
243Am	28Si	271Mt	4n (267Mt)	3 pb	HIVAP	[20]
248Cm	27Al	275Mt	3n (272Mt)	27.83 pb	DNS	[19]
250Cm	27Al	277Mt	5n (272Mt)	97.44 pb	DNS	[19]
249Bk	26Mg	275Mt	4n (271Mt)	9.5 pb	HIVAP	[20]
254Es	22Ne	276Mt	4n (272Mt)	8 pb	HIVAP	[20]
254Es	20Ne	274Mt	4-5n (270,269Mt)	3 pb	HIVAP	[20]

References

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