Isotopes of meitnerium

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Meitnerium (Mt) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial 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 seven 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.

Contents

[edit] Table

nuclide
symbol		 Z(p) N(n)  
isotopic mass (u)
 		 half-life decay
mode(s)		 daughter
isotope(s)		 nuclear
spin
excitation energy
266Mt 109 157 266.13730(37)# 1.2(4) ms α 262Bh
268Mt[n 1] 109 159 268.13873(34)# 21(+8-5) ms α 264Bh 5+#,6+#
268mMt[n 2] 0+X keV 0.07(+10-3) s α 264Bh
270Mt[n 3] 109 161 270.14066(58)# 2# s α 266Bh
270mMt[n 2] α 266Bh
274Mt[n 4] 109 165 274.14749(60)# 20# s α 270Bh
275Mt[n 5] 109 166 275.14865(64)# 9.7(+460-44) ms α 271Bh
276Mt[n 6] 109 167 276.15116(73)# 0.72(+87-25) s α 272Bh
278Mt[n 7] 109 169 278.15481(90)# 7.6 s[1] α 274Bh
  1. ^ Not directly synthesized, occurs as decay product of 272Rg
  2. ^ a b 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 294Uus

[edit] 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.



[edit] Isotopes and nuclear properties

[edit] Nucleosynthesis

[edit] Target-projectile combinations leading to Z=109 compound nuclei

The below table 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
232Th 41K 273Mt Reaction yet to be attempted
231Pa 40Ar 271Mt Reaction yet to be attempted
238U 37Cl 275Mt Failure to date
237Np 36S 275Mt Reaction yet to be attempted
244Pu 31P 275Mt Reaction yet to be attempted
242Pu 31P 273Mt Reaction yet to be attempted
243Am 30Si 273Mt Reaction yet to be attempted
248Cm 27Al 275Mt Reaction yet to be attempted
249Bk 26Mg 275Mt Reaction yet to be attempted
249Cf 23Na 272Mt Reaction yet to be attempted
254Es 22Ne 276Mt Failure to date

[edit] Cold fusion

This section deals with the synthesis of nuclei of meitnerium by so-called "cold" fusion reactions. These are processes which create compound nuclei at low excitation energy (~10–20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only. See more on Cold Fusion

[edit] 209Bi(58Fe,xn)267-xMt (x=1)

The first success in this reaction was in 1982 by the GSI team in their discovery experiment with the identification of a single atom of 266Mt in the 1n neutron evaporation channel.[2] The GSI team used the parent-daughter correlation technique. After an initial failure in 1983, in 1985 the team at the FLNR, Dubna, observed alpha decays from the descendant 246Cf indicating the formation of meitnerium. The GSI synthesised a further 2 atoms of 266Mt in 1988 and continued in 1997 with the detection of 12 atoms during the measurement of the 1n excitation function. [3] [4]

[edit] 208Pb(59Co,xn)267-xMt (x=1)

This reaction was first studied in 1985 by the team in Dubna. They were able to detect the alpha decay of the descendant 246Cf nuclei indicating the formation of meitnerium atoms. In 2007, in a continuation of their study of the effect of odd-Z projectiles on yields of evaporation residues in cold fusion reactions, the team at LBNL synthesised266Mt and were able to correlate the decay with known daughters.[5]

[edit] 181Ta(86Kr,xn)267-xMt

There are indications that this cold fusion reaction using a tantalum target was attempted in August 2001 at the GSI. No details can be found suggesting that no atoms of meitnerium were detected.

[edit] Hot fusion

[edit] 238U(37Cl,xn)275-xMt

In 2002–2003, the team at LBNL attempted the above reaction in order to search for the isotope 271Mt with hope that it may be sufficiently stable to allow a first study of the chemical properties of meitnerium. Unfortunately, no atoms were detected and a cross section limit of 1.5 pb was measured for the 4n channel at the projectile energy used. [6]

[edit] 254Es(22Ne,xn)276-xMt

Attempts to produce long-living isotopes of meitnerium were first performed by Ken Hulet at the Lawrence Livermore National Laboratory (LLNL) in 1988 using the asymmetric hot fusion reaction above. They were unable to detect any product atoms and established a cross section limit of 1 nb.[7]

[edit] As a decay product

Isotopes of meitnerium have also been detected in the decay of heavier elements. Observations to date are shown in the table below:

Evaporation residue Observed Mt isotope
294Uus 278Mt
288Uup 276Mt
287Uup 275Mt
282Uut 274Mt
278Uut 270Mt
272Rg 268Mt

[edit] Chronology of isotope discovery

Isotope Year discovered Discovery reaction
266Mt 1982 209Bi(58Fe,n)[2]
267Mt unknown
268Mt 1994 209Bi(64Ni,n)[8]
269Mt unknown
270Mt 2004 209Bi(70Zn,n)[9]
271Mt unknown
272Mt unknown
273Mt unknown
274Mt 2006 237Np(48Ca,3n)
275Mt 2003 243Am(48Ca,4n)[10]
276Mt 2003 243Am(48Ca,3n)
277Mt unknown
278Mt 2009 249Bk(48Ca,3n)[11]

[edit] Nuclear isomerism

[edit] 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.

[edit] 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.

[edit] Chemical yields of isotopes

[edit] 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

[edit] Theoretical calculations

[edit] 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 [12]
243Am 28Si 271Mt 4n (267Mt) 3 pb HIVAP [12]
249Bk 26Mg 275Mt 4n (271Mt) 9.5 pb HIVAP [12]
254Es 22Ne 276Mt 4n (272Mt) 8 pb HIVAP [12]
254Es 20Ne 274Mt 4-5n (270,269Mt) 3 pb HIVAP [12]

[edit] References

  1. ^ Oganessian, Yu. Ts.; Abdullin, F. Sh.; Bailey, P. D.; Benker, D. E.; Bennett, M. E.; Dmitriev, S. N.; Ezold, J. G.; Hamilton, J. H. et al (2010). "Synthesis of a New Element with Atomic Number Z=117". Physical Review Letters 104. Bibcode 2010PhRvL.104n2502O. doi:10.1103/PhysRevLett.104.142502. PMID 20481935. 
  2. ^ Cite error: Invalid <ref> tag; no text was provided for refs named 82Mu01; see Help:Cite errors/Cite error references no text
  3. ^ Münzenberg, G.; Hofmann, S.; Heßberger, F. P.; Folger, H.; Ninov, V.; Poppensieker, K.; Quint, A. B.; Reisdorf, W. et al (1988). "New results on element 109". Zeitschrift für Physik A 330 (4): 435. Bibcode 1988ZPhyA.330..435M. doi:10.1007/BF01290131. 
  4. ^ Hofmann, S.; Heßberger, F.P.; Ninov, V.; Armbruster, P.; Münzenberg, G.; Stodel, C.; Popeko, A.G.; Yeremin, A.V. et al (1997). "Excitation function for the production of 265 108 and 266 109". Zeitschrift für Physik A 358 (4): 377. Bibcode 1997ZPhyA.358..377H. doi:10.1007/s002180050343. 
  5. ^ Nelson et al. (2009). "Comparison of complementary reactions in the production of Mt". Physical Rev. C 79: 027605. 
  6. ^ "The search for 271Mt via the reaction 238U +37Cl", Zielinski et al.., GSI Annual report, 2003. Retrieved on 2008-03-01
  7. ^ see reference 4 for reference to an internal report from LLNL
  8. ^ see roentgenium for details
  9. ^ see ununtrium for details
  10. ^ see ununpentium for details
  11. ^ Oganessian, Yu. Ts.; Abdullin, F. Sh.; Bailey, P. D.; Benker, D. E.; Bennett, M. E.; Dmitriev, S. N.; Ezold, J. G.; Hamilton, J. H. et al (2010). "Synthesis of a New Element with Atomic Number Z=117". Physical Review Letters 104. Bibcode 2010PhRvL.104n2502O. doi:10.1103/PhysRevLett.104.142502. PMID 20481935. 
  12. ^ a b c d e Wang Kun; et al. (2004). "A Proposed Reaction Channel for the Synthesis of the Superheavy Nucleus Z = 109". Chinese Physics Letters 21 (3): 464. arXiv:nucl-th/0402065. Bibcode 2004ChPhL..21..464W. doi:10.1088/0256-307X/21/3/013. 


Isotopes of hassium Isotopes of meitnerium Isotopes of darmstadtium
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