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Isotopes of meitnerium

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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

List of isotopes

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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:
  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. ^ a b 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. ^ a b 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

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Nucleosynthesis

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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

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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

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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

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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

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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

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Cold fusion

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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

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Evaporation residue cross sections

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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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  3. ^ a b c d Oganessian, Yu. Ts.; Utyonkov, V. K.; Kovrizhnykh, N. D.; et al. (2022). "New isotope 286Mc produced in the 243Am+48Ca reaction". Physical Review C. 106 (64306): 064306. Bibcode:2022PhRvC.106f4306O. doi:10.1103/PhysRevC.106.064306. S2CID 254435744.
  4. ^ a b Oganessian, Yu. Ts.; et al. (2013). "Experimental studies of the 249Bk + 48Ca reaction including decay properties and excitation function for isotopes of element 117, and discovery of the new isotope 277Mt". Physical Review C. 87 (5): 054621. Bibcode:2013PhRvC..87e4621O. doi:10.1103/PhysRevC.87.054621.
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  9. ^ Münzenberg, G.; Hofmann, S.; Heßberger, F. P.; et al. (1988). "New results on element 109". Zeitschrift für Physik A. 330 (4): 435–436. Bibcode:1988ZPhyA.330..435M. doi:10.1007/BF01290131. S2CID 121364541.
  10. ^ Hofmann, S.; Heßberger, F. P.; Ninov, V.; et al. (1997). "Excitation function for the production of 265108 and 266109". Zeitschrift für Physik A. 358 (4): 377–378. Bibcode:1997ZPhyA.358..377H. doi:10.1007/s002180050343. S2CID 124304673.
  11. ^ Nelson, S. L.; Gregorich, K. E.; Dragojević, I.; et al. (2009). "Comparison of complementary reactions in the production of Mt". Physical Review C. 79 (2): 027605. Bibcode:2009PhRvC..79b7605N. doi:10.1103/PhysRevC.79.027605. S2CID 73657127.
  12. ^ a b Zielinski P. M. et al. (2003). "The search for 271Mt via the reaction 238U + 37Cl" Archived 2012-02-06 at the Wayback Machine, GSI Annual report. Retrieved on 2008-03-01
  13. ^ 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. ISBN 1-4020-3555-1.
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  19. ^ a b c d Feng, Z.; Jin, G.; Li, J. (2009). "Production of new superheavy Z=108–114 nuclei with 238U, 244Pu and 248,250Cm targets". Physical Review C. 80: 057601. arXiv:0912.4069. doi:10.1103/PhysRevC.80.057601. S2CID 118733755.
  20. ^ a b c d e Wang, K.; et al. (2004). "A Proposed Reaction Channel for the Synthesis of the Superheavy Nucleus Z = 109". Chinese Physics Letters. 21 (3): 464–467. arXiv:nucl-th/0402065. Bibcode:2004ChPhL..21..464W. doi:10.1088/0256-307X/21/3/013. S2CID 117308338.
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