Livermorium

Livermorium, ₁₁₆Lv

Livermorium
Pronunciation	/ˌlɪvərˈmɔːriəm/ ​(LIV-ər-MOR-ee-əm)
Mass number	[293]
Livermorium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Po ↑ Lv ↓ (Usn) moscovium ← livermorium → tennessine
Atomic number (Z)	116
Group	group 16 (chalcogens)
Period	period 7
Block	p-block
Electron configuration	[Rn] 5f14 6d10 7s2 7p4 (predicted)
Electrons per shell	2, 8, 18, 32, 32, 18, 6 (predicted)
Physical properties
Phase at STP	solid (predicted)
Melting point	637–780 K ​(364–507 °C, ​687–944 °F) (extrapolated)
Boiling point	1035–1135 K ​(762–862 °C, ​1403–1583 °F) (extrapolated)
Density (near r.t.)	12.9 g/cm3 (predicted)
Heat of fusion	7.61 kJ/mol (extrapolated)
Heat of vaporization	42 kJ/mol (predicted)
Atomic properties
Oxidation states	(−2), (+2), (+4) (predicted)
Ionization energies	1st: 663.9 kJ/mol (predicted) 2nd: 1330 kJ/mol (predicted) 3rd: 2850 kJ/mol (predicted) (more)
Atomic radius	empirical: 183 pm (predicted)
Covalent radius	162–166 pm (extrapolated)
Other properties
Natural occurrence	synthetic
CAS Number	54100-71-9
History
Naming	after Lawrence Livermore National Laboratory, itself named partly after Livermore, California
Discovery	Joint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2000)
Isotopes of livermorium
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 290Lv synth 9 ms α 286Fl SF – 291Lv synth 26 ms α 287Fl 292Lv synth 16 ms α 288Fl 293Lv synth 70 ms α 289Fl 293mLv synth 80 ms α ?

Ununhexium is the temporary name of a synthetic superheavy element with the temporary symbol Uuh and atomic number 116. As of December 1, 2011, the name livermorium is in the IUPAC name approval process.

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 the heavier homologue to polonium.

It was first detected in 2000 and since the discovery about 30 atoms of ununhexium have been produced, either directly or as a decay product of ununoctium, and are associated with decays from the four neighbouring isotopes with masses 290–293. The most stable isotope to date is ununhexium-293 with a half-life of ~60 ms.

History

Discovery

On July 19, 2000, scientists at Dubna (JINR) detected a single decay from an atom of ununhexium 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 ²⁹²Uuh due to the correlation of the daughter to previously assigned ²⁸⁸Uuq. However, that assignment was later altered to ²⁸⁹Uuq, and hence this activity was correspondingly changed to ²⁹³Uuh. Two further atoms were reported by the institute during their second experiment between April–May 2001.

$\,_{20}^{48}\mathrm {Ca} +\,_{96}^{248}\mathrm {Cm} \to \,_{116}^{296}\mathrm {Uuh} ^{*}\to \,_{116}^{293}\mathrm {Uuh} +3\,_{0}^{1}\mathrm {n}$

In the same experiment they also detected a decay chain which corresponded to the first observed decay of ununquadium and assigned to ²⁸⁹Uuq. 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 ununhexium, namely ^293bUuh, or a rare decay branch of the already discovered isomer,^293aUuh, 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 ununhexium. The measured decay data confirmed the assignment of the discovery isotope as ²⁹³Uuh. In this run, the team also observed ²⁹²Uuh 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 ununhexium, as ²⁹¹Uuh (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

Ununhexium is historically known as eka-polonium. Ununhexium (Uuh) is a 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 ununhexium was recognized by JWG of IUPAC on 1 June 2011, along with that of ununquadium. According to the vice-director of JINR, the Dubna team would like to name element 116 moscovium, after the Moscow Oblast in which Dubna is located.

As of December 1, 2011, the name livermorium and the symbol Lv are in the IUPAC name approval process. The name recognises the Lawrence Livermore National Laboratory, in Livermore, California, USA, which collaborated with JINR on the discovery.

Current and future experiments

The GSI was to be running an experiment (June 24 – July 25, 2010) to study the formation of ^293,292Uuh in the ²⁴⁸Cm(⁴⁸Ca,xn) reaction as a first step in their future program with a ²⁴⁸Cm target, aiming towards a synthesis of unbinilium.

The team at Dubna have indicated plans to synthesize ununhexium 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 with 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 ²⁹⁴Uuh. In addition, they have future plans to complete the excitation function of the 4n channel product, ²⁹²Uuh, which will allow them to assess the stabilizing effect of the N=184 shell on the yield of evaporation residues.

Isotopes and nuclear properties

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.

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

Cold fusion

²⁰⁸Pb(⁸²Se,xn)^290−xUuh

In 1998, the team at GSI attempted the synthesis of ²⁹⁰Uuh 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 ununhexium 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−xUuh

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−xUuh (x=3,4)

The first attempt to synthesise ununhexium 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 ununhexium. 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 ununhexium, assigned to the isotope ²⁹²Uuh. 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 ²⁹³Uuh 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 ²⁹²Uuh. On this basis, the original data were reassigned to ²⁹³Uuh. The tentative chain is therefore possibly associated with a rare decay branch of this isotope. In this reaction, 2 further atoms of ²⁹³Uuh were detected.

²⁴⁵Cm(⁴⁸Ca,xn)^293−x116 (x=2,3)

In order to assist in the assignment of isotope mass numbers for ununhexium, in March–May 2003 the Dubna team bombarded a ²⁴⁵Cm target with ⁴⁸Ca ions. They were able to observe two new isotopes, assigned to ²⁹¹Uuh and ²⁹⁰Uuh. 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 a decay product

Ununhexium 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 ununhexium.

The observation of ²⁹⁰Uuh 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 ^296,294,290Uuh. Four nuclear reactions have been used, namely ²⁴⁸Cm+⁴⁸Ca, ²⁴⁶Ca+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 ²⁹⁴Uuh using ⁴⁸Ca and ⁵⁰Ti projectiles, the yield from fusion-fission was ~3x less for ⁵⁰Ti, also suggesting a future use in SHE production

Retracted isotopes

²⁸⁹Uuh

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 ²⁸⁹Uuh 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 ununhexium is currently unknown.

Chronology of isotope discovery

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

Yields of isotopes

Hot fusion

The table below provides cross-sections and excitation energies for hot fusion reactions producing ununhexium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile	Target	CN	2n	3n	4n	5n
48Ca	248Cm	296Uuh		1.1 pb, 38.9 MeV	3.3 pb, 38.9 MeV
48Ca	245Cm	293Uuh	0.9 pb, 33.0 MeV	3.7 pb, 37.9 MeV

Theoretical calculations

Decay characteristics

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

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.

DNS = Di-nuclear system; σ = cross section

Target	Projectile	CN	Channel (product)	σmax	Model	Ref
208Pb	82Se	290Uuh	1n (289Uuh)	0.1 pb	DNS
208Pb	79Se	287Uuh	1n (286Uuh)	0.5 pb	DNS
238U	54Cr	292Uuh	2n (290Uuh)	0.1 pb	DNS
250Cm	48Ca	298Uuh	4n (294Uuh)	5 pb	DNS
248Cm	48Ca	296Uuh	4n (292Uuh)	2 pb	DNS
247Cm	48Ca	295Uuh	3n (292Uuh)	3 pb	DNS
245Cm	48Ca	293Uuh	3n (290Uuh)	1.5 pb	DNS

Chemical properties

Extrapolated chemical properties

Oxidation states

Ununhexium 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 +VI is known for all the members apart from oxygen which lacks available d-orbitals for expansion and is limited to a maximum +II state, exhibited in the fluoride OF₂. The +IV 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 ununhexium should portray an oxidizing +IV state and a more stable +II state. The lighter members are also known to form a −II state as oxide, sulfide, selenide, telluride, and polonide.

Chemistry

The possible chemistry of ununhexium can be extrapolated from that of polonium. It should therefore undergo oxidation to a dioxide, UuhO₂, although a trioxide, UuhO₃ is plausible, but unlikely. The stability of a +II state should manifest itself in the formation of a simple monoxide, UuhO. Fluorination will likely result in a tetrafluoride, UuhF₄ and/or a difluoride, UuhF₂. Chlorination and bromination may well stop at the corresponding dihalides, UuhCl₂ and UuhBr₂. Oxidation by iodine should certainly stop at UuhI₂ and may even be inert to this element.

See also

• Island of stability

External links

• Second postcard from the island of stability