Isotopes of ununquadium

Ununquadium (Uuq) 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 ²⁸⁹Uuq in 1999 (or possibly 1998). Ununquadium has five confirmed isotopes, and possibly 2 nuclear isomers. The longest-lived isotope is ²⁸⁹Uuq with a half-life of 2.6 seconds.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin
	excitation energy
285Uuq	114	171	285.18370(111)#	125 ms	α	281Cn	3/2+#
286Uuq	114	172	286.18386(83)#	130 ms	SF (60%)	(variable)	0+
					α (40%)	282Cn
287Uuq	114	173	287.18560(83)#	510(+180-100) ms	α	283Cn
287mUuq				5.5s	α	283Cn
288Uuq	114	174	288.18569(91)#	.8(+27-16) s	α	284Cn	0+
289Uuq	114	175	289.18728(79)#	2.6(+12-7) s	α	285Cn	5/2+#
289mUuq				1.1 min	α	285Cn

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.
• It is theorized that ²⁹⁸Uuq will have a relatively long half-life

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.

Target	Projectile	CN	Attempt result
208Pb	76Ge	284Uuq	Failure to date
232Th	54Cr	286Uuq	Reaction yet to be attempted
238U	50Ti	288Uuq	Reaction yet to be attempted
244Pu	48Ca	292Uuq	Successful reaction
242Pu	48Ca	290Uuq	Successful reaction
239Pu	48Ca	287Uuq	Reaction yet to be attempted
248Cm	40Ar	288Uuq	Reaction yet to be attempted
249Cf	36S	285Uuq	Reaction yet to be attempted

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. The reaction was repeated in 1999 and a further two atoms of ununquadium were detected. The products were assigned to ²⁸⁸Uuq. 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 ²⁸⁹Uuq, twelve atoms of the new isotope ²⁸⁸Uuq, and one atom of the new isotope²⁸⁷Uuq. 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. 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 two atoms of²⁸⁸Uuq 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 nine atoms of the former isotope and four atoms of the latter.

²⁴²Pu(⁴⁸Ca,xn)^290−x114 (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 ²⁸⁷Uuq. The reaction was repeated in September 2003 in order to attempt to confirm the decay data for ²⁸⁷Uuq and ²⁸³Cn since conflicting data for²⁸³Cn 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.

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 two atoms of ununquadium, as²⁸⁷Uuq 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.

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 ²⁸³Cn was detected.

In December 2010, the team at the LBNL announced the synthesis of a single atom of the new isotope ²⁸⁵Uuq with the consequent observation of 5 new isotopes of daughter elements.

As a decay product

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

Evaporation residue	Observed Uuq isotope
293Uuh	289Uuq
292Uuh	288Uuq
291Uuh	287Uuq
294Uuo, 290Uuh	286Uuq

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-lifeof 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 discovery

Isotope	Year discovered	Discovery reaction
285Uuq	2010	242Pu(48Ca,5n)
286Uuq	2002	249Cf(48Ca,3n)
287aUuq	2002	244Pu(48Ca,5n)
287bUuq ??	1999	242Pu(48Ca,3n)
288Uuq	2002	244Pu(48Ca,4n)
289aUuq	1999	244Pu(48Ca,3n)
289bUuq ?	1998	244Pu(48Ca,3n)

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 between⁴⁸Ca and ⁵⁸Fe projectiles, indicating a possible future use of ⁵⁸Fe projectiles in superheavy element formation.

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 of²⁸³Cn. 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

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

Hot fusion

Projectile	Target	CN	2n	3n	4n	5n
48Ca	242Pu	290Uuq	0.5 pb, 32.5 MeV	3.6 pb, 40.0 MeV	4.5 pb, 40.0 MeV	<1.4 pb, 45.0 MeV
48Ca	244Pu	292Uuq		1.7 pb, 40.0 MeV	5.3 pb, 40.0 MeV	1.1 pb, 52.0 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.

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
208Pb	73Ge	281Uuq	1n (280Uuq)	0.2 pb	DNS
238U	50Ti	288Uuq	2n (286Uuq)	60 fb	DNS
244Pu	48Ca	292Uuq	4n (288Uuq)	4 pb	MD
242Pu	48Ca	290Uuq	3n (287Uuq)	3 pb	MD

Decay characteristics

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

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 for²⁹⁷Uup, 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 Q_alpha 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

While evidence for closed neutron shells can be deemed directly from the systematic variation of Q_alpha 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 pairings²⁸²Cn (T_SF1/2 = 0.8 ms) and ²⁸⁶Uuq (T_SF1/2 = 130 ms), and ²⁸⁴Cn (T_SF = 97 ms) and²⁸⁸Uuq (T_SF >800 ms). Further evidence would come from the measurement of partial SF half-lives of nuclei with Z>114, such as²⁹⁰Uuh 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:

204
80Hg + 136
54Xe → 298
114Uuq + 40
20Ca + 2 1
0

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 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:

244
94Pu(96
40Zr, 2n) → 338
134Utq → → 298
114Uuq + 10 4
2He

References

• Isotope masses from:
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf. 
• Isotopic compositions and standard atomic masses from:
  • J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683. http://www.iupac.org/publications/pac/75/6/0683/pdf/. 
  • M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry 78 (11): 2051–2066. doi:10.1351/pac200678112051. http://iupac.org/publications/pac/78/11/2051/pdf/. Lay summary. 
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf. 
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/. Retrieved September 2005. 
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859. 

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