Isotopes of flerovium

Isotopes of flerovium  (₁₁₄Fl)

Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 284Fl synth 2.5 ms [1] [2] SF – α 280Cn 285Fl synth 100 ms [3] α 281Cn 286Fl synth 105 ms [4] α55% 282Cn SF45% – 287Fl synth 360 ms [4] α 283Cn ε? [5] 287Nh 288Fl synth 653 ms α 284Cn 289Fl synth 2.1 s α 285Cn 290Fl synth 19 s? [6] [7] EC 290Nh α 286Cn

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Flerovium (₁₁₄Fl) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was ²⁸⁹Fl in 1999 (or possibly 1998). Flerovium has six known isotopes, along with the unconfirmed ²⁹⁰Fl, and possibly two nuclear isomers. The longest-lived isotope is ²⁸⁹Fl with a half-life of 1.9 seconds, but ²⁹⁰Fl may have a longer half-life of 19 seconds.

List of isotopes

Nuclide	Z	N	Isotopic mass (Da) [8] [n 1] [n 2]	Half-life [9]	Decay mode [9] [n 3]	Daughter isotope	Spin and parity [9] [n 4]
284Fl [1]	114	170	284.18119(70)#	3.1(13) ms	SF	(various)	0+
					α [10]	280Cn
285Fl	114	171	285.18350(43)#	100+60 −30 ms [3]	α	281Cn	3/2+#
286Fl	114	172	286.18423(59)#	105+17 −13 ms [4]	α (55%) [4]	282Cn	0+
					SF (45%)	(various)
287Fl	114	173	287.18672(66)#	360+45 −36 ms [4]	α	283Cn
					EC?	287Nh
288Fl	114	174	288.18778(82)#	653(113) ms	α	284Cn	0+
289Fl	114	175	289.19052(55)#	2.1(6) s	α	285Cn	5/2+#
290Fl [n 5]	114	176	290.19188(75)#	19 s?	EC	290Nh	0+
					α	286Cn
This table header & footer: view

1. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
2. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
3. Modes of decay:

   EC:	Electron capture
   SF:	Spontaneous fission

4. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
5. This isotope is unconfirmed

• It is theorized that ²⁹⁸Fl will have a relatively long half-life, as N = 184 is expected to correspond to a closed neutron shell.

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	284Fl	Failure to date
238U	50Ti	288Fl	Planned reaction [11]
238U	48Ti	286Fl	Reaction yet to be attempted
244Pu	48Ca	292Fl	Successful reaction
242Pu	48Ca	290Fl	Successful reaction [4]
240Pu	48Ca	288Fl	Successful reaction
239Pu	48Ca	287Fl	Successful reaction
250Cm	40Ar	290Fl	Reaction yet to be attempted
248Cm	40Ar	288Fl	Failure to date [12]

Cold fusion

This section deals with the synthesis of nuclei of flerovium 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−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. The team at RIKEN have indicated plans to study this reaction.

Hot fusion

This section deals with the synthesis of nuclei of flerovium 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.

²⁴⁸Cm(⁴⁰Ar,xn)^288-xFl

One of the first attempts at synthesis of superheavy elements was performed by Albert Ghiorso et al. and Stan Thompson et al. in 1968 at the Lawrence Berkeley National Laboratory using this reaction. No events attributable to superheavy nuclei were identified; this was expected as the compound nucleus ²⁸⁸Fl (with N = 174) falls ten neutrons short of the closed shell predicted at N = 184. ^[13] This first unsuccessful synthesis attempt provided early indications of cross-section and half-life limits for superheavy nuclei producible in hot fusion reactions. ^[12]

²⁴⁴Pu(⁴⁸Ca,xn)^292−xFl (x=2?,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 ²⁸⁹
Fl. ^[14] The reaction was repeated in 1999 and a further two atoms of flerovium were detected. The products were assigned to ²⁸⁸
Fl. ^[15] 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 ²⁸⁹
Fl, twelve atoms of the new isotope ²⁸⁸
Fl, and one atom of the new isotope ²⁸⁷Fl. Based on these results, the first atom to be detected was tentatively reassigned to ²⁹⁰
Fl or ^289mFl, whilst the two subsequent atoms were reassigned to ²⁸⁹
Fl and therefore belong to the unofficial discovery experiment. ^[16] In an attempt to study the chemistry of copernicium as the isotope ²⁸⁵
Cn, this reaction was repeated in April 2007. Surprisingly, a PSI-FLNR directly detected two atoms of ²⁸⁸
Fl forming the basis for the first chemical studies of flerovium.

In June 2008, the experiment was repeated in order to further assess the chemistry of the element using the ²⁸⁹
Fl 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 tennessine. The team were able to confirm the synthesis and decay data for ²⁸⁸
Fl and ²⁸⁹
Fl, producing nine atoms of the former isotope and four atoms of the latter. ^{[17] [18]}

²⁴²Pu(⁴⁸Ca,xn)^290−xFl (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. ^[19] The reaction was repeated in September 2003 in order 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. ^{[20] [21]}

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 ²⁴²
Pu 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 ²⁸⁷
Fl and ²⁸⁶
Fl, confirming the decay properties reported at the FLNR, although the measured cross sections were slightly lower; however the statistics were of lower quality. ^[22]

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.

^239,240Pu(⁴⁸Ca,xn)^287,288−xFl (x=3 for ²³⁹Pu; x=3, 4 for ²⁴⁰Pu)

The FLNR had plans to study light isotopes of flerovium, formed in the reaction between ²³⁹Pu or ²⁴⁰Pu and ⁴⁸Ca: in particular, the decay products of ²⁸³Fl and ²⁸⁴Fl were expected to fill in the gap between the isotopes of the lighter superheavy elements formed by cold fusion with ²⁰⁸Pb and ²⁰⁹Bi targets and those formed by hot fusion with ⁴⁸Ca projectiles. These reactions were studied in 2015. One new isotope was found in both the ²⁴⁰Pu(⁴⁸Ca,4n) and ²³⁹Pu(⁴⁸Ca,3n) reactions, the rapidly spontaneously fissioning ²⁸⁴Fl, giving a clear demarcation of the neutron-poor edge of the island of stability. Three atoms of ²⁸⁵Fl were also produced. ^[23] The Dubna team repeated their investigation of the ²⁴⁰Pu+⁴⁸Ca reaction in 2017, observing three new consistent decay chains of ²⁸⁵Fl, an additional decay chain from this nuclide that may pass through some isomeric states in its daughters, a chain that could be assigned to ²⁸⁷Fl (likely stemming from ²⁴²Pu impurities in the target), and some spontaneous fission events of which some could be from ²⁸⁴Fl, though other interpretations including side reactions involving the evaporation of charged particles are also possible. ^[24]

As a decay product

Most of the isotopes of flerovium have also been observed in the decay chains of livermorium and oganesson.

Evaporation residue	Observed Fl isotope
294Lv ??	290Fl ?
293Lv	289Fl [21] [25]
292Lv	288Fl [21]
291Lv	287Fl [16]
294Og, 290Lv	286Fl [26]
288Lv	284Fl [27]

Retracted isotopes

²⁸⁵Fl

In the claimed synthesis of ²⁹³Og 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. 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
284Fl	2015	239Pu(48Ca,3n) 240Pu(48Ca,4n)
285Fl	2010	242Pu(48Ca,5n)
286Fl	2002	249Cf(48Ca,3n) [26]
287Fl	2002	244Pu(48Ca,5n)
288Fl	2002	244Pu(48Ca,4n)
289Fl	1999	244Pu(48Ca,3n)
290Fl ?	1998	244Pu(48Ca,2n)

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 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. ^[28]

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.

It is possible that these decays are due to ²⁹⁰Fl, as the beam energies in these early experiments were set quite low, low enough to make the 2n channel plausible. This assignment necessitates the postulation of undetected electron capture to ²⁹⁰Nh, because it would otherwise be difficult to explain the long half-lives of the daughters of ²⁹⁰Fl to spontaneous fission if they are all even-even. This would suggest that the erstwhile isomeric ^289mFl, ^285mCn, ^281mDs, and ^277mHs are thus actually ²⁹⁰Nh (electron capture of ²⁹⁰Fl having been missed, as current detectors are not sensitive to this decay mode), ²⁸⁶Rg, ²⁸²Mt, and the spontaneously fissioning ²⁷⁸Bh, creating some of the most neutron-rich superheavy isotopes known to date: this fits well with the systematic trend of increasing half-life as neutrons are added to superheavy nuclei towards the beta-stability line, which this chain would then terminate very close to. The livermorium parent could then be assigned to ²⁹⁴Lv, which would have the highest neutron number (178) of all known nuclei, but all these assignments need further confirmation through experiments aimed at reaching the 2n channel in the ²⁴⁴Pu+⁴⁸Ca and ²⁴⁸Cm+⁴⁸Ca reactions. ^[6]

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. It is also possible that this activity is due to the electron capture of a ²⁸⁷Fl residue and actually stems from ²⁸⁷Nh and its daughter ²⁸³Rg. ^[5]

Summary of observed alpha decay chains from superheavy elements with Z = 114, 116, 118, or 120 as of 2016. Assignments for dotted nuclides (including the early Dubna chains 5 and 8 containing Nh and Nh as alternative explanations instead of isomerism in Fl and Fl) are tentative. (Another analysis suggests that chain 3, starting from element 120, is not a real decay chain but a random sequence of events.)

Yields of isotopes

The tables below provide cross-sections and excitation energies for fusion reactions producing flerovium 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	284Fl	<1.2 pb

Hot fusion

Projectile	Target	CN	2n	3n	4n	5n
48Ca	242Pu	290Fl	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	292Fl		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	284Fl	1n (283Fl)	60 fb	DNS	[30]
208Pb	73Ge	281Fl	1n (280Fl)	0.2 pb	DNS	[30]
238U	50Ti	288Fl	2n (286Fl)	60 fb	DNS	[31]
238U	48Ti	286Fl	2n (284Fl)	45.1 fb	DNS	[32]
244Pu	48Ca	292Fl	4n (288Fl)	4 pb	MD	[33]
242Pu	48Ca	290Fl	3n (287Fl)	3 pb	MD	[33]
250Cm	40Ar	290Fl	4n (286Fl)	79.6 fb	DNS	[32]
248Cm	40Ar	288Fl	4n (284Fl)	35 fb	DNS	[32]

Decay characteristics

Theoretical estimation of the alpha decay half-lives of the isotopes of the flerovium supports the experimental data. ^{[34] [35]} The fission-survived isotope ²⁹⁸Fl is predicted to have alpha decay half-life around 17 days. ^{[36] [37]}

In search for the island of stability: ²⁹⁸Fl

Further information: Island of stability

According to macroscopic-microscopic (MM) theory, Z = 114 might be the next spherical magic number. ^{[38] [39]} 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 center of a hypothetical "island of stability" comprising longer-lived superheavy nuclei. 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, and some entirely omit Z = 114 or N = 184. ^{[38] [39]} It is also possible that rather than a peak at a specific proton shell, there exists a plateau of proton shell effects from Z = 114–126.

The island of stability near ²⁹⁸Fl is predicted to enhance stability for its constituent nuclei, especially against spontaneous fission as a consequence of greater fission barrier heights near the shell closure. ^{[38] [40]} Due to the expected high fission barriers, any nucleus within this island of stability will exclusively decay by alpha emission, and as such, the nucleus with the longest half-life may be ²⁹⁸Fl; predictions for the half-life of this nucleus range from minutes to billions of years. ^[41] It may be possible, however, that the longest-lived nuclide is not ²⁹⁸Fl, but instead ²⁹⁷Fl (with N = 183), with the unpaired neutron of the latter nuclide conferring additional stability. ^[42] Other calculations suggest that stability instead peaks in beta-stable isotopes of darmstadtium or copernicium in the vicinity of N = 184 (with half-lives of several hundred years), with flerovium at the upper limit of the stability region. ^{[40] [43]}

Evidence for Z=114 closed proton shell

While evidence for closed neutron shells can be deemed directly from the systematic variation of Q _α 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 ²⁹⁰ Lv and ²⁹² Og (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 with current technology, as no combination of available projectiles and targets may be used to populate nuclei with enough neutrons to be within the island of stability, and radioactive beams (such as ⁴⁴S) cannot be produced with sufficient intensities to make an experiment feasible. ^[43]

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). 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, especially if there are strong shell effects in the region of Z = 114. ^{[43] [44]} If this is indeed possible, one such reaction might be: ^[45]

²³⁸
₉₂U
+ ²³⁸
₉₂U
→ ²⁹⁸
₁₁₄Fl
+ ¹⁷⁸
₇₀Yb

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• Half-life, spin, and isomer data selected from the following sources.
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