Langbahn Team – Weltmeisterschaft

Isotopes of roentgenium

Isotopes of roentgenium (111Rg)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
279Rg synth 0.09 s[2] α87% 275Mt
SF13% –
280Rg synth 3.9 s α 276Mt
281Rg synth 11 s[3] SF86% –
α14% 277Mt
282Rg synth 130 s α 278Mt
283Rg synth 5.1 min?[4] SF –
286Rg synth 10.7 min?[5] α 282Mt

Roentgenium (111Rg) 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 272Rg in 1994, which is also the only directly synthesized isotope; all others are decay products of heavier elements. There are seven known radioisotopes, having mass numbers of 272, 274, and 278–282. The longest-lived isotope is 282Rg with a half-life of about 2 minutes, although the unconfirmed 283Rg and 286Rg may have longer half-lives of about 5.1 minutes and 10.7 minutes respectively.

List of isotopes


Nuclide
 Z N Isotopic mass (Da)
[n 1][n 2] 		Half-life[1]
 Decay
mode[1]
[n 3] 		Daughter
isotope
 Spin and
parity[1]
[n 4]
272Rg 111 161 272.15327(25)# 4.2(11) ms α 268Mt 5+#, 6+#
274Rg[n 5] 111 163 274.15525(23)# 20(11) ms α 270Mt
278Rg[n 6] 111 167 278.16159(42)# 4.6+5.5
−1.6 ms[6] 		α 274Mt
279Rg[n 7] 111 168 279.16288(45)# 90+60
−25 ms[6] 		α (87%) 275Mt
SF (13%)[6] (various)
280Rg[n 8] 111 169 280.16520(57)# 3.9(3) s[6] α (87%) 276Mt
EC (13%)[7] 280Ds
281Rg[n 9] 111 170 281.16676(83)# 11+3
−1 s[6] 		SF (86%) (various)
α (14%)[6] 277Mt[3]
282Rg[n 10] 111 171 282.16934(63)# 130(50) s α 278Mt
283Rg[n 11] 111 172 283.17110(73)# 5.1 min? SF (various)
286Rg[n 12] 111 175 286.17876(49)# 10.7 min? α 282Mt
This table header & footer:
  1. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  3. ^ Modes of decay:
    EC: Electron capture
    SF: Spontaneous fission
  4. ^ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. ^ Not directly synthesized, occurs as a decay product of 278Nh
  6. ^ Not directly synthesized, occurs as a decay product of 282Nh
  7. ^ Not directly synthesized, occurs in decay chain of 287Mc
  8. ^ Not directly synthesized, occurs in decay chain of 288Mc
  9. ^ Not directly synthesized, occurs in decay chain of 293Ts
  10. ^ Not directly synthesized, occurs in decay chain of 294Ts
  11. ^ Not directly synthesized, occurs in decay chain of 287Fl; unconfirmed
  12. ^ Not directly synthesised, occurs in decay chain of 290Fl and 294Lv; unconfirmed

Isotopes and nuclear properties

Nucleosynthesis

Super-heavy elements such as roentgenium are produced by bombarding lighter elements in particle accelerators that induce fusion reactions. Whereas the lightest isotope of roentgenium, roentgenium-272, can be synthesized directly this way, all the heavier roentgenium isotopes have only been observed as decay products of elements with higher atomic numbers.[8]

Depending on the energies involved, fusion reactions can be categorized as "hot" or "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.[9] 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.[8] The latter is a distinct concept from that of where nuclear fusion claimed to be achieved at room temperature conditions (see cold fusion).[10]

The table below contains various combinations of targets and projectiles which could be used to form compound nuclei with Z=111.

Target Projectile CN Attempt result
205Tl 70Zn 275Rg Failure to date
208Pb 65Cu 273Rg Successful reaction
209Bi 64Ni 273Rg Successful reaction
231Pa 48Ca 279Rg Reaction yet to be attempted
238U 41K 279Rg Reaction yet to be attempted
244Pu 37Cl 281Rg Reaction yet to be attempted
248Cm 31P 279Rg Reaction yet to be attempted
250Cm 31P 281Rg Reaction yet to be attempted

Cold fusion

Before the first successful synthesis of roentgenium in 1994 by the GSI team, a team at the Joint Institute for Nuclear Research in Dubna, Russia, also tried to synthesize roentgenium by bombarding bismuth-209 with nickel-64 in 1986. No roentgenium atoms were identified. After an upgrade of their facilities, the team at GSI successfully detected 3 atoms of 272Rg in their discovery experiment.[11] A further 3 atoms were synthesized in 2002.[12] The discovery of roentgenium was confirmed in 2003 when a team at RIKEN measured the decays of 14 atoms of 272Rg.[13]

The same roentgenium isotope was also observed by an American team at the Lawrence Berkeley National Laboratory (LBNL) from the reaction:

208
82Pb
 + 65
29Cu
 → 272
111Rg
 +
n

This reaction was conducted as part of their study of projectiles with odd atomic number in cold fusion reactions.[14]

The 205Tl(70Zn,n)274Rg reaction was tried by the RIKEN team in 2004 and repeated in 2010 in an attempt to secure the discovery of its parent 278Nh:[15]

205
81Tl
 + 70
30Zn
 → 274
111Rg
 +
n

Due to the weakness of the thallium target, they were unable to detect any atoms of 274Rg.[15]

As decay product

List of roentgenium isotopes observed by decay
Evaporation residue Observed roentgenium isotope
294Lv, 290Fl, 290Nh ? 286Rg ?[5]
287Fl, 287Nh ? 283Rg ?[4]
294Ts, 290Mc, 286Nh 282Rg[16]
293Ts, 289Mc, 285Nh 281Rg[16]
288Mc, 284Nh 280Rg[17]
287Mc, 283Nh 279Rg[17]
286Mc, 282Nh 278Rg[17]
278Nh 274Rg[18]

All the isotopes of roentgenium except roentgenium-272 have been detected only in the decay chains of elements with a higher atomic number, such as nihonium. Nihonium currently has six known isotopes, with two more unconfirmed; all of them undergo alpha decays to become roentgenium nuclei, with mass numbers between 274 and 286. Parent nihonium nuclei can be themselves decay products of moscovium and tennessine, and (via unconfirmed branches) flerovium and livermorium.[19] For example, in January 2010, the Dubna team (JINR) identified roentgenium-281 as a final product in the decay of tennessine via an alpha decay sequence:[16]

293
117Ts
 → 289
115Mc
 + 4
2He
289
115Mc
 → 285
113Nh
 + 4
2He
285
113Nh
 → 281
111Rg
 + 4
2He

Nuclear isomerism

274Rg

Two atoms of 274Rg have been observed in the decay chain of 278Nh. They decay by alpha emission, emitting alpha particles with different energies, and have different lifetimes. In addition, the two entire decay chains appear to be different. This suggests the presence of two nuclear isomers but further research is required.[18][failed verification]

272Rg

Four alpha particles emitted from 272Rg with energies of 11.37, 11.03, 10.82, and 10.40 MeV have been detected. The GSI measured 272Rg to have a half-life of 1.6 ms while recent data from RIKEN have given a half-life of 3.8 ms. The conflicting data may be due to nuclear isomers but the current data are insufficient to come to any firm assignments.[11][13]

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing roentgenium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile Target CN 1n 2n 3n
64Ni 209Bi 273Rg 3.5 pb, 12.5 MeV
65Cu 208Pb 273Rg 1.7 pb, 13.2 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; σ = cross section

Target Projectile CN Channel (product) σmax Model Ref
238U 41K 279Rg 4n (275Rg) 0.21 pb DNS [20]
244Pu 37Cl 281Rg 4n (277Rg) 0.33 pb DNS [20]
248Cm 31P 279Rg 4n (275Rg) 1.85 pb DNS [20]
250Cm 31P 281Rg 4n (277Rg) 0.41 pb DNS [20]

References

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Quelle: http://en.wikipedia.org/wiki/Roentgenium-278