Livermorium

Livermorium
116Lv
Po ↑ Lv ↓ (Usn) Periodic table ununpentium ← livermorium → ununseptium
Appearance
unknown
General properties
Name, symbol, number	livermorium, Lv, 116
Pronunciation	/ ˌ l ɪ v ər ˈ m ɔər i ə m / LIV-ər-MOHR-ee-əm
Element category	unknown
Group, period, block	16 (chalcogens), 7, p
Standard atomic weight	[293]
Electron configuration	[Rn] 5f14 6d10 7s2 7p4 (predicted) 2, 8, 18, 32, 32, 18, 6 (predicted)
History
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2000)
Physical properties
Density (near r.t.)	12.9 (predicted) g·cm−3
Atomic properties
Oxidation states	2, 4 (prediction)
Ionization energies	1st: 723.6 (prediction) kJ·mol−1
Covalent radius	175 (estimated) pm
Miscellanea
CAS registry number	54100-71-9
Most stable isotopes
Main article: Isotopes of livermorium
iso NA half-life DM DE ( MeV) DP 293Lv syn 61 ms α 10.54 289Fl 292Lv syn 18 ms α 10.66 288Fl 291Lv syn 18 ms α 10.74 287Fl 290Lv syn 7.1 ms α 10.84 286Fl

Livermorium is the synthetic superheavy element with the symbol Lv and atomic number 116. The name was adopted by IUPAC on May 31, 2012.

It is placed as the heaviest member of group 16 (VIA) although a sufficiently stable isotope is not known at this time to allow chemical experiments to confirm its position as a heavier homologue to polonium.

It was first detected in 2000. Since then, about 35 atoms of livermorium have been produced, either directly or as a decay product of ununoctium, belonging to the four neighbouring isotopes with masses 290–293. The most stable isotope known is livermorium-293 with a half-life of ~60 ms.

History

Unsuccessful synthesis attempts

In late 1998, Polish physicist Robert Smolańczuk published calculations on the fusion of atomic nuclei towards the synthesis of superheavy atoms, including ununoctium. His calculations suggested that it might be possible to make ununoctium and livermorium by fusing lead with krypton under carefully controlled conditions.

In 1999, researchers at Lawrence Berkeley National Laboratory made use of these predictions and announced the discovery of livermorium and ununoctium, in a paper published in Physical Review Letters, and very soon after the results were reported in Science. The researchers reported to have performed the reaction

86
36Kr + 208
82Pb → 293
118Uuo + n.

The following year, they published a retraction after researchers at other laboratories were unable to duplicate the results and the Berkeley lab itself was unable to duplicate them as well. In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by principal author Victor Ninov.

Discovery

On July 19, 2000, scientists at Dubna ( JINR) detected a single decay from an atom of livermorium following the irradiation of a Cm-248 target with Ca-48 ions. The results were published in December 2000. This 10.54 MeV alpha-emitting activity was originally assigned to ²⁹²Lv due to the correlation of the daughter to previously assigned ²⁸⁸Fl. That assignment was later altered to ²⁸⁹Fl, and hence this activity was correspondingly changed to ²⁹³Lv. Two further atoms were reported by the institute during their second experiment between April–May 2001.

In the same experiment they also detected a decay chain which corresponded to the first observed decay of flerovium and assigned to ²⁸⁹Fl. This activity has not been observed again in a repeat of the same reaction. However, its detection in this series of experiments indicates the possibility of the decay of an isomer of livermorium, namely ^293bLv, or a rare decay branch of the already discovered isomer,^293aLv, in which the first alpha particle was missed. Further research is required to positively assign this activity.

The team repeated the experiment in April–May 2005 and detected 8 atoms of livermorium. The measured decay data confirmed the assignment of the discovery isotope as ²⁹³Lv. In this run, the team also observed ²⁹²Lv in the 4n channel for the first time.

In May 2009, the Joint Working Party reported on the discovery of copernicium and acknowledged the discovery of the isotope ²⁸³Cn. This implied the de facto discovery of livermorium, as ²⁹¹Lv (see below), from the acknowledgment of the data relating to the granddaughter ²⁸³Cn, although the actual discovery experiment may be determined as that above.

In 2011, the IUPAC evaluated the Dubna team results and accepted them as a reliable identification of element 116.

Naming

Livermorium is historically known as eka-polonium. Ununhexium (Uuh) was the temporary IUPAC systematic element name. Scientists usually refer to the element simply as element 116 (or E116). According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name.

The discovery of livermorium was recognized by JWG of IUPAC on 1 June 2011, along with that of flerovium. According to the vice-director of JINR, the Dubna team wanted to name element 116 moscovium, after the Moscow Oblast in which Dubna is located. However, the name livermorium and the symbol Lv were adopted on May 31, 2012 after an approval process by the IUPAC. The name recognises the Lawrence Livermore National Laboratory, within the city of Livermore, California, USA, which collaborated with JINR on the discovery. The city in turn is named after the American rancher Robert Livermore, a naturalized Mexican citizen of English birth.

Current and future experiments

The team at Dubna have indicated plans to synthesize livermorium using the reaction between plutonium-244 and titanium-50. This experiment will allow them to assess the feasibility of using projectiles with Z > 20 required in the synthesis of superheavy elements in the eighth period (Z > 118). Although initially scheduled for 2008, the reaction looking at the synthesis of evaporation residues has not been conducted to date.

There are also plans to repeat the Cm-248 reaction at different projectile energies in order to probe the 2n channel, leading to the new isotope ²⁹⁴Lv. In addition, they have future plans to complete the excitation function of the 4n channel product, ²⁹²Lv, which will allow them to assess the stabilizing effect of the N=184 shell on the yield of evaporation residues.

Nucleosynthesis

Target-projectile combinations leading to Z=116 compound nuclei

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 116. The table below provides cross-sections and excitation energies for hot fusion reactions producing livermorium isotopes directly. Data in bold represent maxima derived from excitation function measurements. The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels.

Target	Projectile	CN	Attempt result
208Pb	82Se	290Lv	Failure to date
232Th	58Fe	290Lv	Reaction yet to be attempted
238U	54Cr	292Lv	Failure to date
244Pu	50Ti	294Lv	Reaction yet to be attempted
248Cm	48Ca	296Lv	Successful reaction
246Cm	48Ca	294Lv	Reaction yet to be attempted
245Cm	48Ca	293Lv	Successful reaction
249Cf	40Ar	289Lv	Reaction yet to be attempted

Cold fusion

²⁰⁸Pb(⁸²Se,xn)^290−xLv

In 1998, the team at GSI attempted the synthesis of ²⁹⁰Lv as a radiative capture (x=0) product. No atoms were detected providing a cross section limit of 4.8 pb.

Hot fusion

This section deals with the synthesis of nuclei of livermorium 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.

²³⁸U(⁵⁴Cr,xn)^292−xLv

There are sketchy indications that this reaction was attempted by the team at GSI in 2006. There are no published results on the outcome, presumably indicating that no atoms were detected. This is expected from a study of the systematics of cross sections for ²³⁸U targets.

²⁴⁸Cm(⁴⁸Ca,xn)^296−xLv (x=3,4)

The first attempt to synthesise livermorium was performed in 1977 by Ken Hulet and his team at the Lawrence Livermore National Laboratory (LLNL). They were unable to detect any atoms of livermorium. Yuri Oganessian and his team at the Flerov Laboratory of Nuclear Reactions (FLNR) subsequently attempted the reaction in 1978 and were met by failure. In 1985, a joint experiment between Berkeley and Peter Armbruster's team at GSI, the result was again negative with a calculated cross-section limit of 10–100 pb.

In 2000, Russian scientists at Dubna finally succeeded in detecting a single atom of livermorium, assigned to the isotope ²⁹²Lv. In 2001, they repeated the reaction and formed a further 2 atoms in a confirmation of their discovery experiment. A third atom was tentatively assigned to ²⁹³Lv on the basis of a missed parental alpha decay. In April 2004, the team ran the experiment again at higher energy and were able to detect a new decay chain, assigned to ²⁹²Lv. On this basis, the original data were reassigned to ²⁹³Lv. The tentative chain is therefore possibly associated with a rare decay branch of this isotope. In this reaction, 2 further atoms of ²⁹³Lv were detected.

In an experiment run at the GSI between June-July 2010, scientists detected six atoms of livermorium; two atoms of ²⁹³116 and four atoms of ²⁹²116. They were able to confirm both the decay data and cross sections for the fusion reaction.

²⁴⁵Cm(⁴⁸Ca,xn)^293−x116 (x=2,3)

In order to assist in the assignment of isotope mass numbers for livermorium, in March–May 2003 the Dubna team bombarded a ²⁴⁵Cm target with ⁴⁸Ca ions. They were able to observe two new isotopes, assigned to ²⁹¹Lv and ²⁹⁰Lv. This experiment was successfully repeated in Feb–March 2005 where 10 atoms were created with identical decay data to those reported in the 2003 experiment.

As decay product

Livermorium has also been observed in the decay of ununoctium. In October 2006 it was announced that 3 atoms of ununoctium had been detected by the bombardment of californium-249 with calcium-48 ions, which then rapidly decayed into livermorium.

The observation of ²⁹⁰Lv allowed the assignment of the product to ²⁹⁴Uuo and proved the synthesis of ununoctium.

Fission of compound nuclei with Z=116

Several experiments have been performed between 2000–2006 at the Flerov laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nuclei ^296,294,290Lv. Four nuclear reactions have been used, namely ²⁴⁸Cm+⁴⁸Ca, ²⁴⁶Cm+⁴⁸Ca, ²⁴⁴Pu+⁵⁰Ti and ²³²Th+⁵⁸Fe. 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. In addition, in comparative experiments synthesizing ²⁹⁴Lv using ⁴⁸Ca and ⁵⁰Ti projectiles, the yield from fusion-fission was ~3x less for ⁵⁰Ti, also suggesting a future use in SHE production.

Isotopes and nuclear properties

Chronology of isotope discovery

Isotope	Year discovered	Discovery reaction
290Lv	2002	249Cf(48Ca,3n)
291Lv	2003	245Cm(48Ca,2n)
292Lv	2004	248Cm(48Ca,4n)
293Lv	2000	248Cm(48Ca,3n)

Theoretical calculation in a quantum tunneling model supports the experimental data relating to the synthesis of ^293,292Lv.

Retracted isotope

²⁸⁹Lv

In 1999, researchers at Lawrence Berkeley National Laboratory announced the synthesis of ²⁹³Uuo (see ununoctium), in a paper published in Physical Review Letters. The claimed isotope ²⁸⁹Lv decayed by 11.63 MeV alpha emission with a half-life of 0.64 ms. The following year, they published a retraction after other researchers were unable to duplicate the results. In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by the principal author Victor Ninov. As such, this isotope of livermorium is currently unknown.

Chemical properties

Extrapolated chemical properties

Oxidation states

Livermorium is projected to be the fourth member of the 7p series of non-metals and the heaviest member of group 16 (VIA) in the Periodic Table, below polonium. The group oxidation state of +6 is known for all the members apart from oxygen which lacks available d- orbitals for expansion and is limited to a maximum +2 state, exhibited in the fluoride OF₂. The +4 is known for sulfur, selenium, tellurium, and polonium, undergoing a shift in stability from reducing for S(IV) and Se(IV) to oxidizing in Po(IV). Tellurium(IV) is the most stable for this element. This suggests a decreasing stability for the higher oxidation states as the group is descended and livermorium should portray an oxidizing +4 state and a more stable +2 state. The lighter members are also known to form a −2 state as oxide, sulfide, selenide, telluride, and polonide.

Chemistry

The possible chemistry of livermorium can be extrapolated from that of polonium. It should therefore undergo oxidation to a dioxide, LvO₂, although a trioxide, LvO₃ is plausible, but unlikely. The stability of a +2 state should manifest itself in the formation of a simple monoxide, LvO. Fluorination will likely result in a tetrafluoride, LvF₄ and/or a difluoride, LvF₂; a hexafluoride, LvF₆, is possible but unlikely. Chlorination and bromination may well stop at the corresponding dihalides, LvCl₂ and LvBr₂. Oxidation by iodine should certainly stop at LvI₂ and may even be inert to this element. The heavier livermorium dihalides are predicted to be linear, but the lighter ones are predicted to be bent.