Ununquadium

Ununquadium (pronounced /uːn.uːn.ˈkwɒdiəm/ [1] oon-oon-KWOD-ee-əm) is the temporary name of a radioactive chemical element with the temporary symbol Uuq and atomic number 114.

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 four neighbouring isotopes with mass numbers 286-289. The longest-lived isotope currently known is 289Uuq with a half-life of ~2.6 s, although there is evidence for an isomer, 289bUuq, with a half-life of ~66 s, that would be one of the longest-lived nuclei in the superheavy element region.

Recent chemistry experiments have strongly indicated 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.[2]

History
De facto discovery

In December 1998, scientists at Dubna (Joint Institute for Nuclear Research) in Russia bombarded a 244Pu target with 48Ca 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 289114. This observation was subsequently published in January 1999.[3] 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 289mUuq.

In March 1999, the same team replaced the 244Pu target with a 242Pu 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 287Uuq.[4] 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 287mUuq.

The now-confirmed discovery of ununquadium was made in June 1999 when the Dubna team repeated the 244Pu 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.[5]

This activity was initially assigned to 288Uuq in error, due to the confusion regarding the above observations. Further work in Dec 2002 has allowed a positive reassignment to 289114.[6]

24494Pu + 4820Ca → 292114Uuq* → 289114Uuq + 3 10n

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 283Cn.[7] This therefore implies the de facto discovery of ununquadium, from the acknowledgment of the data for the synthesis of 287Uuq and 291Uuh (see below), relating to 283Cn, although this may not be determined as the first synthesis of the element. An impending report by the JWP will discuss these issues.

The discovery of ununquadium, as 287Uuq and 286Uuq, was confirmed in January 2009 at Berkeley. This was followed by confirmation of 288Uuq and 289Uuq in July 2009 at the GSI (see section 2.1.3).
Naming

Ununquadium (Uuq) is a temporary IUPAC systematic element name. Research scientists usually[citation needed] refer to the element simply as element 114.

According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name.[8] No naming suggestions have yet been given by the (claimant) discoverers.
Current experiments

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. Results are not yet available.
Future experiments

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

²⁰⁸₈₂Pb + ⁷⁶₃₂Ge → ²⁸⁴₁₁₄Uuq* → ?

The Transactinide Separator and Chemistry Apparatus (TASCA) collaboration based at the Gesellschaft für Schwerionenforschung (GSI) will perform their first chemistry experiments on ununquadium starting in August 2009, following their successful production of the element in April 2009.

The FLNR have future plans to study light isotopes of ununquadium, formed in the reaction between 239Pu and 48Ca.
Isotopes and nuclear properties
Nucleosynthesis
Target-Projectile combinations leading to Z=114 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 114.

Cold fusion

This 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.

²⁰⁸Pb(⁷⁶Ge,xn)^284−xUuq

The 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 fusion

This 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 48Ca 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.

²⁴⁴Pu(⁴⁸Ca,xn)^292−xUuq (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 289Uuq.[3] The reaction was repeated in 1999 and a further 2 atoms of ununquadium were detected. The products were assigned to 288Uuq.[5] 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 3 atoms of 289Uuq, 12 atoms of the new isotope 288Uuq, and 1 atom of the new isotope 287Uuq. Based on these results, the first atom to be detected was tentatively reassigned to 290Uuq or 289mUuq, whilst the two subsequent atoms were reassigned to 289Uuq and therefore belong to the unofficial discovery experiment.[6] In an attempt to study the chemistry of copernicium as the isotope 285Cn, this reaction was repeated in April 2007. Surprisingly, a PSI-FLNR directly detected 2 atoms of 288Uuq 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 289Uuq 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 288Uuq and 289Uuq, producing 9 atoms of the former isotope and 4 atoms of the latter.[9]

²⁴²Pu(⁴⁸Ca,xn)^290−x114 (x=2,3,4)

The team at Dubna first studied this reaction in March-April 1999 and detected two atoms of ununquadium, assigned to 287Uuq.[4] The reaction was repeated in September 2003 in order to attempt to confirm the decay data for 287Uuq and 283Cn since conflicting data for 283Cn had been collected (see copernicium). The Russian scientists were able to measure decay data for 288Uuq, 287Uuq and the new isotope 286Uuq from the measurement of the 2n, 3n, and 4n excitation functions. [10] [11]
In April 2006, a PSI-FLNR collaboration used the reaction to determine the first chemical properties of copernicium by producing 283Cn as an overshoot product. In a confirmatory experiment in April 2007, the team were able to detect 287Uuq directly and therefore measure some initial data on the atomic chemical properties of ununquadium.
The team at Berkeley, using the Berkeley gas-filled separator (BGS), continued their studies using newly acquired 242Pu 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 2 atoms of ununquadium, as 287Uuq and 286Uuq, confirming the decay properties reported at the FLNR, although the measured cross sections were slightly lower; however the statistics were of lower quality.[12]
As a decay product

The isotopes of ununquadium have also been observed in the decay chains of ununhexium and ununoctium.

Retracted isotopes
285Uuq

In the claimed synthesis of 293Uuo in 1999, the isotope 285Uuq was identified as decaying by 11.35 MeV alpha emission with a half-life of 0.58 ms. The claim was retracted in 2001 and hence this ununquadium isotope is currently unknown or unconfirmed.
Chronology of isotope discovery

Fission of compound nuclei with an atomic number of 114

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.[15]
Nuclear isomerism
289Uuq

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

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

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

Hot fusion

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.

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

Decay characteristics

Theoretical estimation of the alpha decay half-lives of the isotopes of the ununquadium supports the experimental data.[19][20] The fission-survived isotope 298Uuq is predicted to have alpha decay half life around 17 days.[21][22]
In search for the island of stability: 298Uuq

According to macroscopic-microscopic (MM) theory[citation needed], 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.[citation needed] 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

Whilst 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

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 10n

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.[23]

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
Extrapolated chemical properties
Oxidation states

Ununquadium is projected to be the second member of the 7p series of non-metals 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

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.[2]
Experimental chemistry
Atomic gas phase

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.[24]
See also

* Island of stability: Ununquadium–Unbinilium–Unbihexium
* Lead
* Periodic table (extended)
* Isotopes of ununquadium

References

1. ^ J. Chatt (1979). "Recommendations for the Naming of Elements of Atomic Numbers Greater than 100". Pure Appl. Chem. 51: 381–384. doi:10.1351/pac197951020381.
2. ^ a b Gas Phase Chemistry of Superheavy Elements, lecture by Heinz W. Gäggeler, Nov. 2007. Last accessed on Dec. 12, 2008.
3. ^ a b Oganessian, Yu. Ts. (1999). "Synthesis of Superheavy Nuclei in the ^{48}Ca+ ^{244}Pu Reaction". Physical Review Letters 83: 3154. doi:10.1103/PhysRevLett.83.3154.
4. ^ a b Yeremin, A. V. (1999). "Synthesis of nuclei of the superheavy element 114 in reactions induced by 48Ca". Nature 400: 242. doi:10.1038/22281.
5. ^ a b Oganessian, Yu. Ts. (2000). "Synthesis of superheavy nuclei in the 48Ca+244Pu reaction: 288114". Physical Review C 62: 041604. doi:10.1103/PhysRevC.62.041604.
6. ^ a b c Oganessian, Yu. Ts. (2004). "Measurements of cross sections for the fusion-evaporation reactions 244Pu(48Ca,xn)292−x114 and 245Cm(48Ca,xn)293−x116". Physical Review C 69: 054607. doi:10.1103/PhysRevC.69.054607.
7. ^ R.C.Barber; H.W.Gaeggeler;P.J.Karol;H. Nakahara; E.Verdaci; E. Vogt (2009). "Discovery of the element with atomic number 112" (IUPAC Technical Report). Pure Appl. Chem. 81: 1331. doi:10.1351/PAC-REP-08-03-05. http://media.iupac.org/publications/pac/asap/pdf/PAC-REP-08-03-05.pdf.
8. ^ Koppenol, W. H. (2002). "Naming of new elements(IUPAC Recommendations 2002)" (PDF). Pure and Applied Chemistry 74: 787. doi:10.1351/pac200274050787. http://media.iupac.org/publications/pac/2002/pdf/7405x0787.pdf.
9. ^ Element 114 - Heaviest Element at GSI Observed at TASCA
10. ^ Oganessian, Yu. Ts. (2004). "Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactions 233,238U, 242Pu, and 248Cm+48Ca". Physical Review C 70: 064609. doi:10.1103/PhysRevC.70.064609.
11. ^ a b c "Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactions 233,238U , 242Pu , and 248Cm+48Ca", Oganessian et al., JINR preprints, 2004. Retrieved on 2008-03-03
12. ^ Stavsetra, L. (2009). "Independent Verification of Element 114 Production in the 48Ca+242Pu Reaction". Physical Review Letters 103: 132502. doi:10.1103/PhysRevLett.103.132502.
13. ^ see ununhexium
14. ^ a b see ununoctium
15. ^ see Flerov lab annual reports 2000-2006
16. ^ a b Feng, Zhao-Qing (2007). "Formation of superheavy nuclei in cold fusion reactions". Physical Review C 76: 044606. doi:10.1103/PhysRevC.76.044606. http://arxiv.org/pdf/0707.2588.
17. ^ Feng, Z (2009). "Production of heavy and superheavy nuclei in massive fusion reactions". Nuclear Physics A 816: 33. doi:10.1016/j.nuclphysa.2008.11.003. http://arxiv.org/pdf/0803.1117.
18. ^ a b Zagrebaev, V (2004). "Fusion-fission dynamics of super-heavy element formation and decay" (PDF). Nuclear Physics A 734: 164. doi:10.1016/j.nuclphysa.2004.01.025. http://nrv.jinr.ru/pdf_file/npa_04.pdf.
19. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu (January 26, 2006). "α decay half-lives of new superheavy elements". Phys. Rev. C 73: 014612. doi:10.1103/PhysRevC.73.014612.
20. ^ C. Samanta, P. Roy Chowdhury and D.N. Basu (2007). "Predictions of alpha decay half lives of heavy and superheavy elements". Nucl. Phys. A 789: 142–154. doi:10.1016/j.nuclphysa.2007.04.001.
21. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2008). "Search for long lived heaviest nuclei beyond the valley of stability". Phys. Rev. C 77: 044603. doi:10.1103/PhysRevC.77.044603.
22. ^ P. Roy Chowdhury, C. Samanta, and D. N. Basu (2008). "Nuclear half-lives for α-radioactivity of elements with 100 ≤ Z ≤ 130". At. Data & Nucl. Data Tables 94: 781–806. doi:10.1016/j.adt.2008.01.003.
23. ^ Zagrebaev, V; Greiner, W (2008). "Synthesis of superheavy nuclei: A search for new production reactions". Physical Review C 78: 034610. doi:10.1103/PhysRevC.78.034610. http://arxiv.org/pdf/0807.2537v1.
24. ^ Flerov Lab

External links

* WebElements.com: Ununquadium
* First postcard from the island of nuclear stability
* Second postcard from the island of stability