Utente:KeyboardSpellbounder/Eptafluoropropano

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Voci in creazione[modifica | modifica wikitesto]

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History[modifica | modifica wikitesto]

Naming[modifica | modifica wikitesto]

Ununquadium (Uuq) is a temporary IUPAC systematic element name. The element is often referred to as element 114, for its atomic number.

According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name.[1] The discovery of ununquadium was recognized by JWG of IUPAC on 1 June 2011, along with that of ununhexium.[2] According to the vice-director of JINR,[3] the Dubna team would like to name element 114 flerovium,[4] after Soviet physicist Georgy Flyorov (also spelled Flerov).

Future experiments[modifica | modifica wikitesto]

The team at RIKEN have indicated plans to study the cold fusion reaction:

20882Pb + 7632Ge → 284114Uuq* → ?

The FLNR have future plans to study light isotopes of ununquadium, formed in the reaction between 239Pu and 48Ca.

Isotopes and nuclear properties[modifica | modifica wikitesto]

Nucleosynthesis[modifica | modifica wikitesto]

Fission of compound nuclei with an atomic number of 114[modifica | modifica wikitesto]

Several experiments have been performed between 2000–2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus 292Uuq. The nuclear reaction used is 244Pu+48Ca. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as 132Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between 48Ca and 58Fe projectiles, indicating a possible future use of 58Fe projectiles in superheavy element formation.[5]

Nuclear isomerism[modifica | modifica wikitesto]

289Uuq[modifica | modifica wikitesto]

In the first claimed synthesis of ununquadium, an isotope assigned as 289Uuq decayed by emitting a 9.71 MeV alpha particle with a lifetime of 30 seconds. This activity was not observed in repetitions of the direct synthesis of this isotope. However, in a single case from the synthesis of 293Uuh, a decay chain was measured starting with the emission of a 9.63 MeV alpha particle with a lifetime of 2.7 minutes. All subsequent decays were very similar to that observed from 289Uuq, presuming that the parent decay was missed. This strongly suggests that the activity should be assigned to an isomeric level. The absence of the activity in recent experiments indicates that the yield of the isomer is ~20% compared to the supposed ground state and that the observation in the first experiment was a fortunate (or not as the case history indicates). Further research is required to resolve these issues.

287Uuq[modifica | modifica wikitesto]

In a manner similar to those for 289Uuq, first experiments with a 242Pu target identified an isotope 287Uuq decaying by emission of a 10.29 MeV alpha particle with a lifetime of 5.5 seconds. The daughter spontaneously fissioned with a lifetime in accord with the previous synthesis of 283Cn. Both these activities have not been observed since (see copernicium). However, the correlation suggests that the results are not random and are possible due to the formation of isomers whose yield is obviously dependent on production methods. Further research is required to unravel these discrepancies.

Yields of isotopes[modifica | modifica wikitesto]

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

Cold fusion[modifica | modifica wikitesto]

Projectile Target CN 1n 2n 3n
76Ge 208Pb 284Uuq <1.2 pb

Theoretical calculations[modifica | modifica wikitesto]

Evaporation residue cross sections[modifica | modifica wikitesto]

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.

MD = multi-dimensional; DNS = Dinuclear system; σ = cross section

Target Projectile CN Channel (product) σmax Model Ref
208Pb 76Ge 284Uuq 1n (283Uuq) 60 fb DNS [6]
208Pb 73Ge 281Uuq 1n (280Uuq) 0.2 pb DNS [6]
238U 50Ti 288Uuq 2n (286Uuq) 60 fb DNS [7]
244Pu 48Ca 292Uuq 4n (288Uuq) 4 pb MD [8]
242Pu 48Ca 290Uuq 3n (287Uuq) 3 pb MD [8]

Decay characteristics[modifica | modifica wikitesto]

Theoretical estimation of the alpha decay half-lives of the isotopes of the ununquadium supports the experimental data.[9][10] The fission-survived isotope 298Uuq is predicted to have alpha decay half life around 17 days.[11][12]

In search for the island of stability: 298Uuq[modifica | modifica wikitesto]

According to macroscopic-microscopic (MM) theory[senza fonte], Z=114 is the next spherical magic number. This means that such nuclei are spherical in their ground state and should have high, wide fission barriers to deformation and hence long SF partial half-lives.

In the region of Z=114, MM theory indicates that N=184 is the next spherical neutron magic number and puts forward the nucleus 298Uuq as a strong candidate for the next spherical doubly magic nucleus, after 208Pb (Z=82, N=126). 298Uuq is taken to be at the centre of a hypothetical "island of stability". However, other calculations using relativistic mean field (RMF) theory propose Z=120, 122, and 126 as alternative proton magic numbers depending upon the chosen set of parameters. It is possible that rather than a peak at a specific proton shell, there exists a plateau of proton shell effects from Z=114–126.

It should be noted that calculations suggest that the minimum of the shell-correction energy and hence the highest fission barrier exists for 297Uup, caused by pairing effects. Due to the expected high fission barriers, any nucleus within this island of stability will exclusively decay by alpha-particle emission and as such the nucleus with the longest half-life is predicted to be 298Uuq. The expected half-life is unlikely to reach values higher than about 10 minutes, unless the N=184 neutron shell proves to be more stabilising than predicted, for which there exists some evidence.[senza fonte] In addition, 297Uuq may have an even-longer half-life due to the effect of the odd neutron, creating transitions between similar Nilsson levels with lower Qalpha values.

In either case, an island of stability does not represent nuclei with the longest half-lives but those which are significantly stabilized against fission by closed-shell effects.

Evidence for Z=114 closed proton shell[modifica | modifica wikitesto]

While evidence for closed neutron shells can be deemed directly from the systematic variation of Qalpha values for ground-state to ground-state transitions, evidence for closed proton shells comes from (partial) spontaneous fission half-lives. Such data can sometimes be difficult to extract due to low production rates and weak SF branching. In the case of Z=114, evidence for the effect of this proposed closed shell comes from the comparison between the nuclei pairings 282Cn (TSF1/2 = 0.8 ms) and 286Uuq (TSF1/2 = 130 ms), and 284Cn (TSF = 97 ms) and 288Uuq (TSF >800 ms). Further evidence would come from the measurement of partial SF half-lives of nuclei with Z>114, such as 290Uuh and 292Uuo (both N=174 isotones). The extraction of Z=114 effects is complicated by the presence of a dominating N=184 effect in this region.

Difficulty of synthesis of 298Uuq[modifica | modifica wikitesto]

The direct synthesis of the nucleus 298Uuq by a fusion-evaporation pathway is impossible since no known combination of target and projectile can provide 184 neutrons in the compound nucleus.

It has been suggested that such a neutron-rich isotope can be formed by the quasifission (partial fusion followed by fission) of a massive nucleus. Such nuclei tend to fission with the formation of isotopes close to the closed shells Z=20/N=20 (40Ca), Z=50/N=82 (132Sn) or Z=82/N=126 (208Pb/209Bi). If Z=114 does represent a closed shell, then the hypothetical reaction below may represent a method of synthesis:

20480Hg + 13654Xe → 298114Uuq + 4020Ca + 2 10

Recently it has been shown that the multi-nucleon transfer reactions in collisions of actinide nuclei (such as uranium and curium) might be used to synthesize the neutron rich superheavy nuclei located at the island of stability.[13]

It is also possible that 298Uuq can be synthesized by the alpha decay of a massive nucleus. Such a method would depend highly on the SF stability of such nuclei, since the alpha half-lives are expected to be very short. The yields for such reactions will also most likely be extremely small. One such reaction is:

24494Pu(9640Zr, 2n) → 338134Utq → → 298114Uuq + 10 42He

Chemical properties[modifica | modifica wikitesto]

Extrapolated chemical properties[modifica | modifica wikitesto]

Oxidation states[modifica | modifica wikitesto]

Ununquadium is projected to be the second member of the 7p series of chemical elements and the heaviest member of group 14 (IVA) in the Periodic Table, below lead. Each of the members of this group show the group oxidation state of +IV and the latter members have an increasing +II chemistry due to the onset of the inert pair effect. Tin represents the point at which the stability of the +II and +IV states are similar. Lead, the heaviest member, portrays a switch from the +IV state to the +II state. Ununquadium should therefore follow this trend and a possess an oxidising +IV state and a stable +II state.

Chemistry[modifica | modifica wikitesto]

Ununquadium should portray eka-lead chemical properties and should therefore form a monoxide, UuqO, and dihalides, UuqF2, UuqCl2, UuqBr2, and UuqI2. If the +IV state is accessible, it is likely that it is only possible in the oxide, UuqO2, and fluoride, UuqF4. It may also show a mixed oxide, Uuq3O4, analogous to Pb3O4.

Some studies also suggest that the chemical behaviour of ununquadium might in fact be closer to that of the noble gas radon, than to that of lead.[14]

Experimental chemistry[modifica | modifica wikitesto]

Atomic gas phase[modifica | modifica wikitesto]

Two experiments were performed in April–May 2007 in a joint FLNR-PSI collaboration aiming to study the chemistry of copernicium. The first experiment involved the reaction 242Pu(48Ca,3n)287Uuq and the second the reaction 244Pu(48Ca,4n)288Uuq. The adsorption properties of the resultant atoms on a gold surface were compared with those of radon. The first experiment allowed detection of 3 atoms of 283Cn but also seemingly detected 1 atom of 287Uuq. This result was a surprise given the transport time of the product atoms is ~2 s, so ununquadium atoms should decay before adsorption. In the second reaction, 2 atoms of 288Uuq and possibly 1 atom of 289Uuq were detected. Two of the three atoms portrayed adsorption characteristics associated with a volatile, noble-gas-like element, which has been suggested but is not predicted by more recent calculations. These experiments did however provide independent confirmation for the discovery of copernicium, ununquadium, and ununhexium via comparison with published decay data. Further experiments were performed in 2008 to confirm this important result and a single atom of 289Uuq was detected which gave data in agreement with previous data in support of ununquadium having a noble-gas-like interaction with gold.[15] In April 2009, the FLNR-PSI collaboration synthesized a further atom of element 114.

See also[modifica | modifica wikitesto]

References[modifica | modifica wikitesto]

  1. ^ Koppenol, W. H., Naming of new elements(IUPAC Recommendations 2002) (PDF), in Pure and Applied Chemistry, vol. 74, 2002, p. 787, DOI:10.1351/pac200274050787.
  2. ^ Barber, Robert C.; Karol, Paul J; Nakahara, Hiromichi; Vardaci, Emanuele; Vogt, Erich W., Discovery of the elements with atomic numbers greater than or equal to 113 (IUPAC Technical Report), in Pure Appl. Chem., 2011, DOI:10.1351/PAC-REP-10-05-01.
  3. ^ Russian Physicists Will Suggest to Name Element 116 Moscovium, su rian.ru, 2011. URL consultato l'8 maggio 2011.: Mikhail Itkis, the vice-director of JINR stated: "We would like to name element 114 after Georgy Flerov – flerovium, and another one [element 116] – moscovium, not after Moscow, but after Moscow Oblast".
  4. ^ (English) Mark Brown, Two Ultraheavy Elements Added to Periodic Table, Wired, June 6, 2011. URL consultato il 7 June 2011. Lingua sconosciuta: English (aiuto)
  5. ^ see Flerov lab annual reports 2000–2006
  6. ^ a b Feng, Zhao-Qing, Formation of superheavy nuclei in cold fusion reactions, in Physical Review C, vol. 76, 2007, p. 044606, DOI:10.1103/PhysRevC.76.044606.
  7. ^ Feng, Z, Production of heavy and superheavy nuclei in massive fusion reactions, in Nuclear Physics A, vol. 816, 2009, DOI:10.1016/j.nuclphysa.2008.11.003.
  8. ^ a b Zagrebaev, V, Fusion-fission dynamics of super-heavy element formation and decay (PDF), in Nuclear Physics A, vol. 734, 2004, DOI:10.1016/j.nuclphysa.2004.01.025.
  9. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu, α decay half-lives of new superheavy elements, in Phys. Rev. C, vol. 73, January 26, 2006, p. 014612, DOI:10.1103/PhysRevC.73.014612.
  10. ^ C. Samanta, P. Roy Chowdhury and D.N. Basu, Predictions of alpha decay half lives of heavy and superheavy elements, in Nucl. Phys. A, vol. 789, 2007, pp. 142–154, DOI:10.1016/j.nuclphysa.2007.04.001.
  11. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu, Search for long lived heaviest nuclei beyond the valley of stability, in Phys. Rev. C, vol. 77, 2008, p. 044603, DOI:10.1103/PhysRevC.77.044603.
  12. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu, Nuclear half-lives for α-radioactivity of elements with 100 ≤ Z ≤ 130, in At. Data & Nucl. Data Tables, vol. 94, 2008, pp. 781–806, DOI:10.1016/j.adt.2008.01.003.
  13. ^ Zagrebaev, V; Greiner, W, Synthesis of superheavy nuclei: A search for new production reactions, in Physical Review C, vol. 78, 2008, p. 034610, DOI:10.1103/PhysRevC.78.034610.
  14. ^ Errore nelle note: Errore nell'uso del marcatore <ref>: non è stato indicato alcun testo per il marcatore tanm
  15. ^ Flerov Lab

External links[modifica | modifica wikitesto]

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