Flerovium

Flerovium
114Fl
Pb ↑ Fl ↓ (Uho) Periodic table ununtrium ← flerovium → ununpentium
Appearance
unknown
General properties
Name, symbol, number	flerovium, Fl, 114
Pronunciation	/ f l ɨ ˈ r oʊ v i ə m / fli-ROH-vee-əm
Element category	unknown
Group, period, block	14, 7, p
Standard atomic weight	[289]
Electron configuration	[Rn] 5f14 6d10 7s2 7p2 (predicted) 2, 8, 18, 32, 32, 18, 4 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (1999)
Physical properties
Phase	solid (predicted)
Density (near r.t.)	22 (predicted) g·cm−3
Melting point	340 K, 70 °C, 160 (predicted) °F
Boiling point	420 K, 150 °C, 300 (predicted) °F
Atomic properties
Oxidation states	2, 4 (prediction)
Ionization energies	1st: 823.9 (prediction) kJ·mol−1
	2nd: 1621.0 (prediction) kJ·mol−1
Atomic radius	160 (estimated) pm
Covalent radius	143 (estimated) pm
Miscellanea
CAS registry number	54085-16-4
Most stable isotopes
Main article: Isotopes of flerovium
iso NA half-life DM DE ( MeV) DP 289Fl syn 2.6 s α 9.82,9.48 285Cn 289mFl ? syn 1.1 min α 9.67 285mCn ? 288Fl syn 0.8 s α 9.94 284Cn 287Fl syn 0.48 s α 10.02 283Cn 287mFl ?? syn 5.5 s α 10.29 283mCn ?? 286Fl syn 0.13 s 40% α 10.19 282Cn 60% SF 285Fl syn 125 ms α 281Cn

Flerovium is the radioactive chemical element with the symbol "Fl" and atomic number 114. The element is named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna, Russia, where the element was discovered. The name of the laboratory, in turn, honours the Russian physicist Georgy Flyorov. The name was adopted by IUPAC on May 30, 2012.

About 80 decays of atoms of flerovium have been observed to date, 50 directly and 30 from the decay of the heavier elements livermorium and ununoctium. All decays have been assigned to the five neighbouring isotopes with mass numbers 285–289. The longest-lived isotope currently known is ²⁸⁹Fl with a half-life of ~2.6 s, although there is evidence for a nuclear isomer, ^289bFl, 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 2007–2008 indicate that flerovium is unexpectedly volatile for a group 14 element; in preliminary results it even seemed to exhibit noble-gas-like properties due to relativistic effects.

History

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 flerovium, decaying by 9.67 MeV alpha-emission with a half-life of 30 s, was produced and assigned to ²⁸⁹Fl. 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 ^289mFl.

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 flerovium were produced, decaying by 10.29 MeV alpha-emission with a half-life of 5.5 s. They were assigned as ²⁸⁷Fl. 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 ^287mFl.

The now-confirmed discovery of flerovium 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.

This activity was initially assigned to ²⁸⁸Fl in error, due to the confusion regarding the above observations. Further work in Dec 2002 has allowed a positive reassignment to ²⁸⁹Fl.

244
94Pu + 48
20Ca → 292
114Fl → 289
114Fl + 3 1
0n

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. This therefore implies the de facto discovery of flerovium, from the acknowledgment of the data for the synthesis of ²⁸⁷Fl and ²⁹¹Lv (see below), relating to ²⁸³Cn. 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 flerovium, as ²⁸⁷Fl and ²⁸⁶Fl, was confirmed in January 2009 at Berkeley. This was followed by confirmation of ²⁸⁸Fl and ²⁸⁹Fl in July 2009 at the GSI (see section 2.1.3).

Naming

Ununquadium (Uuq) was the 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 chose to name element 114 flerovium (symbol Fl), after the founder of the Russian institute, Flerov Laboratory of Nuclear Reactions, the Soviet physicist Georgy Flyorov (also spelled Flerov). However, IUPAC officially named flerovium after the Flerov Laboratory of Nuclear Reactions, not after Flerov himself. Flerov is known for writing to Stalin in April 1942 and pointing out the conspicuous silence in scientific journals within the field of nuclear fission in the United States, Great Britain, and Germany. Flyorov deduced that this research must have become classified information in those countries. Flyorov's work and urgings led to the eventual development of the USSR's own atomic bomb project.

Future experiments

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

208
82Pb + 76
32Ge → 284
114Fl → ?

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

Nucleosynthesis

Target-projectile combinations leading to Z=114 compound nuclei

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

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

Cold fusion

This section deals with the synthesis of nuclei of flerovium by so-called "cold" fusion reactions. These processes 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−xFl

The first attempt to synthesise flerovium 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 flerovium by so-called "hot" fusion reactions. These processes 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−xFl (x=3,4,5)

The first experiments on the synthesis of flerovium were performed by the team in Dubna in November 1998. They were able to detect a single, long decay chain, assigned to ²⁸⁹Fl. The reaction was repeated in 1999 and a further two atoms of flerovium were detected. The products were assigned to ²⁸⁸Fl. 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 ²⁸⁹Fl, twelve atoms of the new isotope ²⁸⁸Fl, and one atom of the new isotope ²⁸⁷Fl. Based on these results, the first atom to be detected was tentatively reassigned to ²⁹⁰Fl or ^289mFl, whilst the two subsequent atoms were reassigned to ²⁸⁹Fl 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 of ²⁸⁸Fl forming the basis for the first chemical studies of flerovium.

In June 2008, the experiment was repeated to further assess the chemistry of the element using the ²⁸⁹Fl 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 ²⁸⁸Fl and ²⁸⁹Fl, 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 flerovium, assigned to ²⁸⁷Fl. The reaction was repeated in September 2003 to attempt to confirm the decay data for ²⁸⁷Fl and ²⁸³Cn since conflicting data for ²⁸³Cn had been collected (see copernicium). The Russian scientists were able to measure decay data for ²⁸⁸Fl, ²⁸⁷Fl and the new isotope ²⁸⁶Fl 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 ²⁸⁷Fl directly and therefore measure some initial data on the atomic chemical properties of flerovium.

The team at Berkeley, using the Berkeley gas-filled separator (BGS), continued their studies using newly acquired ²⁴²Pu targets by attempting the synthesis of flerovium in January 2009 using the above reaction. In September 2009, they reported that they had succeeded in detecting two atoms of flerovium, as ²⁸⁷Fl and ²⁸⁶Fl, 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 flerovium 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 ²⁸⁵Fl with the consequent observation of 5 new isotopes of daughter elements.

As a decay product

The isotopes of flerovium have also been observed in the decay chains of livermorium and ununoctium.

Evaporation residue	Observed Fl isotope
293Lv	289Fl
292Lv	288Fl
291Lv	287Fl
294Uuo, 290Lv	286Fl

Isotopes and nuclear properties

Chronology of isotope discovery

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

Retracted isotopes

²⁸⁵Fl

In the claimed synthesis of ²⁹³Uuo in 1999, the isotope ²⁸⁵Fl was identified as decaying by 11.35 MeV alpha emission with a half-life of 0.58 ms. The claim was retracted in 2001 after it was discovered that the data has been fabricated. This isotope was finally created in 2010 and its decay properties did not match the retracted decay data.

Fission of compound nuclei with an atomic number of 114

Several experiments have been performed between 2000 and 2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus ²⁹²Fl. The nuclear reaction used is 244
94Pu +  48
20Ca. 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.

Nuclear isomerism

²⁸⁹Fl

In the first claimed synthesis of flerovium, an isotope assigned as ²⁸⁹Fl 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 ²⁹³Lv, 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 ²⁸⁹Fl, 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.

²⁸⁷Fl

In a manner similar to those for ²⁸⁹Fl, first experiments with a ²⁴²Pu target identified an isotope ²⁸⁷Fl 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.

Decay characteristics

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

In search for the island of stability: ²⁹⁸Fl

According 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 ²⁹⁸Fl as a strong candidate for the next spherical doubly magic nucleus, after ²⁰⁸Pb (Z=82, N=126). ²⁹⁸Fl 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 exclusively decays by alpha-particle emission and, as such, the nucleus with the longest half-life is predicted to be ²⁹⁸Fl. 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, ²⁹⁷Fl 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 that 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 pairings ²⁸²Cn (T_SF1/2 = 0.8 ms) and ²⁸⁶Fl (T_SF1/2 = 130 ms), and ²⁸⁴Cn (T_SF = 97 ms) and ²⁸⁸Fl (T_SF > 800 ms). Further evidence would come from the measurement of partial SF half-lives of nuclei with Z>114, such as ²⁹⁰Lv 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 ²⁹⁸Fl

The direct synthesis of the nucleus ²⁹⁸Fl 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
114Fl + 40
20Ca + 2 1
0n

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 ²⁹⁸Fl 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
114Fl + 10 4
2He

Chemical properties

Extrapolated chemical properties

Oxidation states

Flerovium 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. Flerovium should therefore follow this trend and a possess an oxidising +IV state and a stable +II state.

Chemistry

Flerovium should portray eka-lead chemical properties and should therefore form a monoxide, FlO, and dihalides, FlF₂, FlCl₂, FlBr₂, and FlI₂. If the +IV state is accessible, it is likely that it is only possible in the oxide, FlO₂, and fluoride, FlF₄. It may also show a mixed oxide, Fl₃O₄, analogous to Pb₃O₄.

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

Calculations suggest that flerovium will not form a tetrafluoride, FlF₄, but will form a difluoride (FlF₂) that is soluble in water.

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)²⁸⁷Fl and the second the reaction ²⁴⁴Pu(⁴⁸Ca,4n)²⁸⁸Fl. 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 ²⁸⁷Fl. This result was a surprise given the transport time of the product atoms is ~2 s, so flerovium atoms should decay before adsorption. In the second reaction, 2 atoms of ²⁸⁸Fl and possibly 1 atom of ²⁸⁹Fl 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, flerovium, and livermorium via comparison with published decay data. Further experiments in 2008 to confirm this important result detected a single atom of ²⁸⁹Fl—which provided data that agreed with previous data that supported flerovium having a noble-gas-like interaction with gold.

In April 2009, the FLNR-PSI collaboration synthesized a further atom of flerovium.