Ununquadium
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| Appearance | ||||||
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| General properties | ||||||
| Name, symbol, number | ununquadium, Uuq, 114 | |||||
| Pronunciation |  /uːn.uːn.ˈkwɒdiəm/oon-oon-kwod-ee-əm | |||||
| Category notes | Unknown, suspected to be a noble gas | |||||
| Group, period, block | 14, 7, p | |||||
| Standard atomic weight | [289] | |||||
| Electron configuration | perhaps [Rn] 5f 6d 7s 7p (guess based on lead) | |||||
| Electrons per shell | 2, 8, 18, 32, 32, 18, 4 (Image) | |||||
| Physical properties | ||||||
| Phase | Unknown | |||||
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| Miscellanea | ||||||
| CAS registry number | 54085-16-4 | |||||
| Most stable isotopes | ||||||
| Main article: Isotopes of ununquadium | ||||||
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Ununquadium ( About 80 decays of atoms of ununquadium have been observed to date, 50 directly and 30 from the decay of the heavier elements ununhexium and ununoctium. All decays have been assigned to the five neighbouring isotopes with mass numbers 285–289. The longest-lived isotope currently known is Uuq with a half-life of ~2.6 s, although there is evidence for a nuclear isomer, Uuq, with a half-life of ~66 s, that would be one of the longest-lived nuclei in the superheavy element region. Chemical studies performed in 2007 strongly indicate that ununquadium possesses non-eka-lead properties and appears to behave as the first superheavy element that portrays noble-gas-like properties due to relativistic effects. HistoryDiscoveryIn December 1998, scientists at Dubna (Joint Institute for Nuclear Research) in Russia bombarded a Pu target with Ca ions. A single atom of ununquadium, decaying by 9.67 MeV alpha-emission with a half-life of 30 s, was produced and assigned to 114. This observation was subsequently published in January 1999. However, the decay chain observed has not been repeated and the exact identity of this activity is unknown, although it is possible that it is due to a meta-stable isomer, namely Uuq. In March 1999, the same team replaced the Pu target with a Pu one in order to produce other isotopes. This time two atoms of ununquadium were produced, decaying by 10.29 MeV alpha-emission with a half-life of 5.5 s. They were assigned as Uuq. Once again, this activity has not been seen again and it is unclear what nucleus was produced. It is possible that it was a meta-stable isomer, namely Uuq. The now-confirmed discovery of ununquadium was made in June 1999 when the Dubna team repeated the Pu reaction. This time, two atoms of element 114 were produced decaying by emission of 9.82 MeV alpha particles with a half life of 2.6 s. This activity was initially assigned to Uuq in error, due to the confusion regarding the above observations. Further work in Dec 2002 has allowed a positive reassignment to 114.
In May 2009, the Joint Working Party (JWP) of IUPAC published a report on the discovery of copernicium in which they acknowledged the discovery of the isotope Cn. This therefore implies the de facto discovery of ununquadium, from the acknowledgment of the data for the synthesis of Uuq and Uuh (see below), relating to Cn. In 2011, IUPAC evaluated the Dubna team experiments of 1999–2007. Whereas they found the early data inconclusive, the results of 2004–2007 were accepted as identification of element 114. The discovery of ununquadium, as Uuq and Uuq, was confirmed in January 2009 at Berkeley. This was followed by confirmation of Uuq and Uuq in July 2009 at the GSI (see section 2.1.3). NamingUnunquadium (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. The discovery of ununquadium was recognized by JWG of IUPAC on 1 June 2011, along with that of ununhexium. According to the vice-director of JINR, the Dubna team would like to name element 114 flerovium, after Soviet physicist Georgy Flyorov (also spelled Flerov). Future experimentsThe team at RIKEN have indicated plans to study the cold fusion reaction:
The FLNR have future plans to study light isotopes of ununquadium, formed in the reaction between Pu and Ca. Isotopes and nuclear propertiesNucleosynthesisTarget-Projectile combinations leading to Z=114 compound nucleiThe below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 114. Cold fusionThis section deals with the synthesis of nuclei of ununquadium 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. Pb(Ge,xn)UuqThe first attempt to synthesise ununquadium in cold fusion reactions was performed at Grand accélérateur national d'ions lourds (GANIL), France in 2003. No atoms were detected providing a yield limit of 1.2 pb. Hot fusionThis section deals with the synthesis of nuclei of ununquadium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40–50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3–5 neutrons. Fusion reactions utilizing Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30–35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions. Pu(Ca,xn)Uuq (x=3,4,5)The first experiments on the synthesis of ununquadium were performed by the team in Dubna in November 1998. They were able to detect a single, long decay chain, assigned to Uuq. The reaction was repeated in 1999 and a further two atoms of ununquadium were detected. The products were assigned to Uuq. The team further studied the reaction in 2002. During the measurement of the 3n, 4n, and 5n neutron evaporation excitation functions they were able to detect three atoms of Uuq, twelve atoms of the new isotope Uuq, and one atom of the new isotope Uuq. Based on these results, the first atom to be detected was tentatively reassigned to Uuq or Uuq, whilst the two subsequent atoms were reassigned to Uuq and therefore belong to the unofficial discovery experiment. In an attempt to study the chemistry of copernicium as the isotope Cn, this reaction was repeated in April 2007. Surprisingly, a PSI-FLNR directly detected two atoms of Uuq forming the basis for the first chemical studies of ununquadium. In June 2008, the experiment was repeated in order to further assess the chemistry of the element using the Uuq isotope. A single atom was detected seeming to confirm the noble-gas-like properties of the element. During May–July 2009, the team at GSI studied this reaction for the first time, as a first step towards the synthesis of ununseptium. The team were able to confirm the synthesis and decay data for Uuq and Uuq, producing nine atoms of the former isotope and four atoms of the latter. Pu(Ca,xn)114 (x=2,3,4,5)The team at Dubna first studied this reaction in March–April 1999 and detected two atoms of ununquadium, assigned to Uuq. The reaction was repeated in September 2003 in order to attempt to confirm the decay data for Uuq and Cn since conflicting data for Cn had been collected (see copernicium). The Russian scientists were able to measure decay data for Uuq, Uuq and the new isotope Uuq from the measurement of the 2n, 3n, and 4n excitation functions. In April 2006, a PSI-FLNR collaboration used the reaction to determine the first chemical properties of copernicium by producing Cn as an overshoot product. In a confirmatory experiment in April 2007, the team were able to detect Uuq directly and therefore measure some initial data on the atomic chemical properties of ununquadium. The team at Berkeley, using the (BGS), continued their studies using newly acquired Pu targets by attempting the synthesis of ununquadium in January 2009 using the above reaction. In September 2009, they reported that they had succeeded in detecting two atoms of ununquadium, as Uuq and Uuq, confirming the decay properties reported at the FLNR, although the measured cross sections were slightly lower; however the statistics were of lower quality. In April 2009, the collaboration of Paul Scherrer Institute (PSI) and Flerov Laboratory of Nuclear Reactions (FLNR) of JINR carried out another study of the chemistry of ununquadium using this reaction. A single atom of Cn was detected. In December 2010, the team at the LBNL announced the synthesis of a single atom of the new isotope Uuq with the consequent observation of 5 new isotopes of daughter elements. As a decay productThe isotopes of ununquadium have also been observed in the decay chains of ununhexium and ununoctium. Retracted isotopesUuqIn the claimed synthesis of Uuo in 1999, the isotope Uuq was identified as decaying by 11.35 MeV alpha emission with a half-life of 0.58 ms. The claim was retracted in 2001. This isotope was finally created in 2010 and its decay properties supported the fabrication of the previously published decay data. Chronology of isotope discoveryFission of compound nuclei with an atomic number of 114Several experiments have been performed between 2000–2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus Uuq. The nuclear reaction used is Pu+Ca. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between Ca and Fe projectiles, indicating a possible future use of Fe projectiles in superheavy element formation. Nuclear isomerismUuqIn the first claimed synthesis of ununquadium, an isotope assigned as Uuq 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 Uuh, 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 Uuq, 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. UuqIn a manner similar to those for Uuq, first experiments with a Pu target identified an isotope Uuq 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 Cn. 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 isotopesThe 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 fusionHot fusionTheoretical calculationsEvaporation residue cross sectionsThe 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 Decay characteristicsTheoretical estimation of the alpha decay half-lives of the isotopes of the ununquadium supports the experimental data. The fission-survived isotope Uuq is predicted to have alpha decay half life around 17 days. In search for the island of stability: UuqAccording to macroscopic-microscopic (MM) theory, 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 Uuq as a strong candidate for the next spherical doubly magic nucleus, after Pb (Z=82, N=126). Uuq 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 Uup, 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 Uuq. 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. In addition, Uuq 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 shellWhile 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 Cn (TSF1/2 = 0.8 ms) and Uuq (TSF1/2 = 130 ms), and Cn (TSF = 97 ms) and Uuq (TSF >800 ms). Further evidence would come from the measurement of partial SF half-lives of nuclei with Z>114, such as Uuh and Uuo (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 UuqThe direct synthesis of the nucleus Uuq 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 (Ca), Z=50/N=82 (Sn) or Z=82/N=126 (Pb/Bi). If Z=114 does represent a closed shell, then the hypothetical reaction below may represent a method of synthesis:
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. It is also possible that Uuq 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:
Chemical propertiesExtrapolated chemical propertiesOxidation statesUnunquadium 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. ChemistryUnunquadium 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. Experimental chemistryAtomic gas phaseTwo 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 Pu(Ca,3n)Uuq and the second the reaction Pu(Ca,4n)Uuq. 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 Cn but also seemingly detected 1 atom of Uuq. 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 Uuq and possibly 1 atom of Uuq 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 Uuq was detected which gave data in agreement with previous data in support of ununquadium having a noble-gas-like interaction with gold. In April 2009, the FLNR-PSI collaboration synthesized a further atom of element 114. See alsoReferencesExternal links
Retrieved from : http://en.wikipedia.org/wiki/Ununquadium 
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