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= Livermorium =
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Introduction
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Livermorium is a synthetic chemical element; it has symbol Lv and
atomic number 116. It is an extremely radioactive element that has
only been created in a laboratory setting and has not been observed in
nature. The element is named after the Lawrence Livermore National
Laboratory in the United States, which collaborated with the Joint
Institute for Nuclear Research (JINR) in Dubna, Russia, to discover
livermorium during experiments conducted between 2000 and 2006. The
name of the laboratory refers to the city of Livermore, California,
where it is located, which in turn was named after the rancher and
landowner Robert Livermore. The name was adopted by IUPAC on May 30,
2012. Six isotopes of livermorium are known, with mass numbers of
288-293 inclusive; the longest-lived among them is livermorium-293
with a half-life of about 80 milliseconds. A seventh possible isotope
with mass number 294 has been reported but not yet confirmed.
In the periodic table, it is a p-block transactinide element. It is a
member of the 7th period and is placed in group 16 as the heaviest
chalcogen, but it has not been confirmed to behave as the heavier
homologue to the chalcogen polonium. Livermorium is calculated to have
some similar properties to its lighter homologues (oxygen, sulfur,
selenium, tellurium, and polonium), and be a post-transition metal,
though it should also show several major differences from them.
Unsuccessful synthesis attempts
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The first search for element 116, using the reaction between 248Cm and
48Ca, 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) in the Joint Institute for
Nuclear Research (JINR) subsequently attempted the reaction in 1978
and met failure. In 1985, in 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. Work on reactions with
48Ca, which had proved very useful in the synthesis of nobelium from
the natPb+48Ca reaction, nevertheless continued at Dubna, with a
superheavy element separator being developed in 1989, a search for
target materials and starting of collaborations with LLNL being
started in 1990, production of more intense 48Ca beams being started
in 1996, and preparations for long-term experiments with 3 orders of
magnitude higher sensitivity being performed in the early 1990s. This
work led directly to the production of new isotopes of elements 112 to
118 in the reactions of 48Ca with actinide targets and the discovery
of the 5 heaviest elements on the periodic table: flerovium,
moscovium, livermorium, tennessine, and oganesson.
In 1995, an international team led by Sigurd Hofmann at the
Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany
attempted to synthesise element 116 in a radiative capture reaction
(in which the compound nucleus de-excites through pure gamma emission
without evaporating neutrons) between a lead-208 target and
selenium-82 projectiles. No atoms of element 116 were identified.
Unconfirmed discovery claims
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In late 1998, Polish physicist Robert Smolańczuk published
calculations on the fusion of atomic nuclei towards the synthesis of
superheavy atoms, including elements 118 and 116. His calculations
suggested that it might be possible to make these two elements 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 elements 118 and
116, 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
: + → + → + α
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. The isotope 289Lv was finally
discovered in 2024 at the JINR.
Discovery
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Livermorium was first synthesized on July 19, 2000, when scientists at
Dubna (JINR) bombarded a curium-248 target with accelerated calcium-48
ions. A single atom was detected, decaying by alpha emission with
decay energy 10.54 MeV to an isotope of flerovium. The results were
published in December 2000.
: + → * → + 3 → + α
The daughter flerovium isotope had properties matching those of a
flerovium isotope first synthesized in June 1999, which was originally
assigned to 288Fl, implying an assignment of the parent livermorium
isotope to 292Lv. Later work in December 2002 indicated that the
synthesized flerovium isotope was actually 289Fl, and hence the
assignment of the synthesized livermorium atom was correspondingly
altered to 293Lv.
Road to confirmation
======================
Two further atoms were reported by the institute during their second
experiment during April-May 2001. In the same experiment they also
detected a decay chain which corresponded to the first observed decay
of flerovium in December 1998, which had been assigned to 289Fl. No
flerovium isotope with the same properties as the one found in
December 1998 has ever been observed again, even in repeats of the
same reaction. Later it was found that 289Fl has different decay
properties and that the first observed flerovium atom may have been
its nuclear isomer 289mFl. The observation of 289mFl in this series of
experiments may indicate the formation of a parent isomer of
livermorium, namely 293mLv, or a rare and previously unobserved decay
branch of the already-discovered state 293Lv to 289mFl. Neither
possibility is certain, and research is required to positively assign
this activity. Another possibility suggested is the assignment of the
original December 1998 atom to 290Fl, as the low beam energy used in
that original experiment makes the 2n channel plausible; its parent
could then conceivably be 294Lv, but this assignment would still need
confirmation in the 248Cm(48Ca,2n)294Lv reaction.
The team repeated the experiment in April-May 2005 and detected 8
atoms of livermorium. The measured decay data confirmed the assignment
of the first-discovered isotope as 293Lv. In this run, the team also
observed the isotope 292Lv for the first time. In further experiments
from 2004 to 2006, the team replaced the curium-248 target with the
lighter curium isotope curium-245. Here evidence was found for the two
isotopes 290Lv and 291Lv.
In May 2009, the IUPAC/IUPAP Joint Working Party reported on the
discovery of copernicium and acknowledged the discovery of the isotope
283Cn. This implied the 'de facto' discovery of the isotope 291Lv,
from the acknowledgment of the data relating to its granddaughter
283Cn, although the livermorium data was not absolutely critical for
the demonstration of copernicium's discovery. Also in 2009,
confirmation from Berkeley and the Gesellschaft für
Schwerionenforschung (GSI) in Germany came for the flerovium isotopes
286 to 289, immediate daughters of the four known livermorium
isotopes. In 2011, IUPAC evaluated the Dubna team experiments of
2000-2006. Whereas they found the earliest data (not involving 291Lv
and 283Cn) inconclusive, the results of 2004-2006 were accepted as
identification of livermorium, and the element was officially
recognized as having been discovered.
The synthesis of livermorium has been separately confirmed at the GSI
(2012) and RIKEN (2014 and 2016). In the 2012 GSI experiment, one
chain tentatively assigned to 293Lv was shown to be inconsistent with
previous data; it is believed that this chain may instead originate
from an isomeric state, 293mLv. In the 2016 RIKEN experiment, one atom
that may be assigned to 294Lv was seemingly detected, alpha decaying
to 290Fl and 286Cn, which underwent spontaneous fission; however, the
first alpha from the livermorium nuclide produced was missed, and the
assignment to 294Lv is still uncertain though plausible.
Naming
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Using Mendeleev's nomenclature for unnamed and undiscovered elements,
livermorium is sometimes called 'eka-polonium'. In 1979 IUPAC
recommended that the placeholder systematic element name 'ununhexium'
('Uuh') be used until the discovery of the element was confirmed and a
name was decided. Although widely used in the chemical community on
all levels, from chemistry classrooms to advanced textbooks, the
recommendations were mostly ignored among scientists in the field, who
called it "element 116", with the symbol of 'E116', '(116)', or even
simply '116'.
According to IUPAC recommendations, the discoverer or discoverers of a
new element have the right to suggest a name. The discovery of
livermorium was recognized by the Joint Working Party (JWP) of IUPAC
on 1 June 2011, along with that of flerovium. According to the
vice-director of JINR, the Dubna team originally wanted to name
element 116 'moscovium', after the Moscow Oblast in which Dubna is
located, but it was later decided to use this name for element 115
instead. The name 'livermorium' and the symbol 'Lv' were adopted on
May 23, 2012. The name recognises the Lawrence Livermore National
Laboratory, within the city of Livermore, California, US, 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. The naming ceremony for flerovium and
livermorium was held in Moscow on October 24, 2012.
Other routes of synthesis
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The synthesis of livermorium in fusion reactions using projectiles
heavier than 48Ca has been explored in preparation for synthesis
attempts of the yet-undiscovered element 120, as such reactions would
necessarily utilize heavier projectiles. In 2023, the reaction between
238U and 54Cr was studied at the JINR's Superheavy Element Factory in
Dubna; one atom of the new isotope 288Lv was reported, though more
detailed analysis has not yet been published. Similarly, in 2024, a
team at the Lawrence Berkeley National Laboratory reported the
synthesis of two atoms of 290Lv in the reaction between 244Pu and
50Ti. This result was described as "truly groundbreaking" by RIKEN
director Hiromitsu Haba, whose team plans to search for element 119.
The team at JINR studied the reaction between 242Pu and 50Ti in 2024
as a follow-up to the 238U+54Cr, obtaining additional decay data for
288Lv and its decay products and discovering the new isotope 289Lv.
Predicted properties
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Other than nuclear properties, no properties of livermorium or its
compounds have been measured; this is due to its extremely limited and
expensive production and the fact that it decays very quickly.
Properties of livermorium remain unknown and only predictions are
available.
Nuclear stability and isotopes
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Livermorium is expected to be near an island of stability centered on
copernicium (element 112) and flerovium (element 114). Due to the
expected high fission barriers, any nucleus within this island of
stability exclusively decays by alpha decay and perhaps some electron
capture and beta decay. While the known isotopes of livermorium do not
actually have enough neutrons to be on the island of stability, they
can be seen to approach the island, as the heavier isotopes are
generally the longer-lived ones.
Superheavy elements are produced by nuclear fusion. These fusion
reactions can be divided into "hot" and "cold" fusion, depending on
the excitation energy of the compound nucleus produced. In hot fusion
reactions, very light, high-energy projectiles are accelerated toward
very heavy targets (actinides), giving rise to compound nuclei at high
excitation energy (~40-50 MeV) that may either fission or evaporate
several (3 to 5) neutrons. In cold fusion reactions (which use heavier
projectiles, typically from the fourth period, and lighter targets,
usually lead and bismuth), the produced fused nuclei have a relatively
low excitation energy (~10-20 MeV), which decreases the probability
that these products will undergo fission reactions. As the fused
nuclei cool to the ground state, they require emission of only one or
two neutrons. Hot fusion reactions tend to produce more neutron-rich
products because the actinides have the highest neutron-to-proton
ratios of any elements that can presently be made in macroscopic
quantities.
Important information could be gained regarding the properties of
superheavy nuclei by the synthesis of more livermorium isotopes,
specifically those with a few neutrons more or less than the known
ones - 286Lv, 287Lv, 294Lv, and 295Lv. This is possible because there
are many reasonably long-lived isotopes of curium that can be used to
make a target. The light isotopes can be made by fusing curium-243
with calcium-48. They would undergo a chain of alpha decays, ending at
transactinide isotopes that are too light to achieve by hot fusion and
too heavy to be produced by cold fusion. The same neutron-deficient
isotopes are also reachable in reactions with projectiles heavier than
48Ca, which will be necessary to reach elements beyond atomic number
118 (or possibly 119); this is how 288Lv and 289Lv were discovered.
The synthesis of the heavy isotopes 294Lv and 295Lv could be
accomplished by fusing the heavy curium isotope curium-250 with
calcium-48. The cross section of this nuclear reaction would be about
1 picobarn, though it is not yet possible to produce 250Cm in the
quantities needed for target manufacture. Alternatively, 294Lv could
be produced via charged-particle evaporation in the 251Cf(48Ca,pn)
reaction. After a few alpha decays, these livermorium isotopes would
reach nuclides at the line of beta stability. Additionally, electron
capture may also become an important decay mode in this region,
allowing affected nuclei to reach the middle of the island. For
example, it is predicted that 295Lv would alpha decay to 291Fl, which
would undergo successive electron capture to 291Nh and then 291Cn
which is expected to be in the middle of the island of stability and
have a half-life of about 1200 years, affording the most likely hope
of reaching the middle of the island using current technology. A
drawback is that the decay properties of superheavy nuclei this close
to the line of beta stability are largely unexplored.
Other possibilities to synthesize nuclei on the island of stability
include quasifission (partial fusion followed by fission) of a massive
nucleus. Such nuclei tend to fission, expelling doubly magic or nearly
doubly magic fragments such as calcium-40, tin-132, lead-208, or
bismuth-209. 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, although formation of the
lighter elements nobelium or seaborgium is more favored. One last
possibility to synthesize isotopes near the island is to use
controlled nuclear explosions to create a neutron flux high enough to
bypass the gaps of instability at 258-260Fm and at mass number 275
(atomic numbers 104 to 108), mimicking the r-process in which the
actinides were first produced in nature and the gap of instability
around radon bypassed. Some such isotopes (especially 291Cn and 293Cn)
may even have been synthesized in nature, but would have decayed away
far too quickly (with half-lives of only thousands of years) and be
produced in far too small quantities (about 10−12 the abundance of
lead) to be detectable as primordial nuclides today outside cosmic
rays.
Physical and atomic
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In the periodic table, livermorium is a member of group 16, the
chalcogens. It appears below oxygen, sulfur, selenium, tellurium, and
polonium. Every previous chalcogen has six electrons in its valence
shell, forming a valence electron configuration of ns2np4. In
livermorium's case, the trend should be continued and the valence
electron configuration is predicted to be 7s27p4; therefore,
livermorium will have some similarities to its lighter congeners.
Differences are likely to arise; a large contributing effect is the
spin-orbit (SO) interaction--the mutual interaction between the
electrons' motion and spin. It is especially strong for the superheavy
elements, because their electrons move much faster than in lighter
atoms, at velocities comparable to the speed of light. In relation to
livermorium atoms, it lowers the 7s and the 7p electron energy levels
(stabilizing the corresponding electrons), but two of the 7p electron
energy levels are stabilized more than the other four. The
stabilization of the 7s electrons is called the inert pair effect, and
the effect "tearing" the 7p subshell into the more stabilized and the
less stabilized parts is called subshell splitting. Computation
chemists see the split as a change of the second (azimuthal) quantum
number 'l' from 1 to and for the more stabilized and less stabilized
parts of the 7p subshell, respectively: the 7p1/2 subshell acts as a
second inert pair, though not as inert as the 7s electrons, while the
7p3/2 subshell can easily participate in chemistry. For many
theoretical purposes, the valence electron configuration may be
represented to reflect the 7p subshell split as 7s7p7p.
Inert pair effects in livermorium should be even stronger than in
polonium and hence the +2 oxidation state becomes more stable than the
+4 state, which would be stabilized only by the most electronegative
ligands; this is reflected in the expected ionization energies of
livermorium, where there are large gaps between the second and third
ionization energies (corresponding to the breaching of the unreactive
7p1/2 shell) and fourth and fifth ionization energies. Indeed, the 7s
electrons are expected to be so inert that the +6 state will not be
attainable. The melting and boiling points of livermorium are expected
to continue the trends down the chalcogens; thus livermorium should
melt at a higher temperature than polonium, but boil at a lower
temperature. It should also be denser than polonium (α-Lv: 12.9 g/cm3;
α-Po: 9.2 g/cm3); like polonium it should also form an α and a β
allotrope.
The electron of a hydrogen-like livermorium atom (oxidized so that it
only has one electron, Lv115+) is expected to move so fast that it has
a mass 1.86 times that of a stationary electron, due to relativistic
effects. For comparison, the figures for hydrogen-like polonium and
tellurium are expected to be 1.26 and 1.080 respectively.
Chemical
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Livermorium is projected to be the fourth member of the 7p series of
chemical elements and the heaviest member of group 16 in the periodic
table, below polonium. While it is the least theoretically studied of
the 7p elements, its chemistry is expected to be quite similar to that
of polonium. The group oxidation state of +6 is known for all the
chalcogens apart from oxygen which cannot expand its octet and is one
of the strongest oxidizing agents among the chemical elements. Oxygen
is thus limited to a maximum +2 state, exhibited in the fluoride OF2.
The +4 state is known for sulfur, selenium, tellurium, and polonium,
undergoing a shift in stability from reducing for sulfur(IV) and
selenium(IV) through being the most stable state for tellurium(IV) to
being oxidizing in polonium(IV). This suggests a decreasing stability
for the higher oxidation states as the group is descended due to the
increasing importance of relativistic effects, especially the inert
pair effect. The most stable oxidation state of livermorium should
thus be +2, with a rather unstable +4 state. The +2 state should be
about as easy to form as it is for beryllium and magnesium, and the +4
state should only be achieved with strongly electronegative ligands,
such as in livermorium(IV) fluoride (LvF4). The +6 state should not
exist at all due to the very strong stabilization of the 7s electrons,
making the valence core of livermorium only four electrons. The
lighter chalcogens are also known to form a −2 state as oxide,
sulfide, selenide, telluride, and polonide; due to the destabilization
of livermorium's 7p3/2 subshell, the −2 state should be very unstable
for livermorium, whose chemistry should be essentially purely
cationic, though the larger subshell and spinor energy splittings of
livermorium as compared to polonium should make Lv2− slightly less
unstable than expected.
Livermorium hydride (LvH2) would be the heaviest chalcogen hydride and
the heaviest homolog of water (the lighter ones are H2S, H2Se, H2Te,
and PoH2). Polane (polonium hydride) is a more covalent compound than
most metal hydrides because polonium straddles the border between
metal and metalloid and has some nonmetallic properties: it is
intermediate between a hydrogen halide like hydrogen chloride (HCl)
and a metal hydride like stannane (SnH4). Livermorane should continue
this trend: it should be a hydride rather than a livermoride, but
still a covalent molecular compound. Spin-orbit interactions are
expected to make the Lv-H bond longer than expected from periodic
trends alone, and make the H-Lv-H bond angle larger than expected:
this is theorized to be because the unoccupied 8s orbitals are
relatively low in energy and can hybridize with the valence 7p
orbitals of livermorium. This phenomenon, dubbed "supervalent
hybridization", has some analogues in non-relativistic regions in the
periodic table; for example, molecular calcium difluoride has 4s and
3d involvement from the calcium atom. The heavier livermorium
dihalides are predicted to be linear, but the lighter ones are
predicted to be bent.
Experimental chemistry
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Unambiguous determination of the chemical characteristics of
livermorium has not yet been established. In 2011, experiments were
conducted to create nihonium, flerovium, and moscovium isotopes in the
reactions between calcium-48 projectiles and targets of americium-243
and plutonium-244. The targets included lead and bismuth impurities
and hence some isotopes of bismuth and polonium were generated in
nucleon transfer reactions. This, while an unforeseen complication,
could give information that would help in the future chemical
investigation of the heavier homologs of bismuth and polonium, which
are respectively moscovium and livermorium. The produced nuclides
bismuth-213 and polonium-212m were transported as the hydrides 213BiH3
and 212mPoH2 at 850 °C through a quartz wool filter unit held with
tantalum, showing that these hydrides were surprisingly thermally
stable, although their heavier congeners McH3 and LvH2 would be
expected to be less thermally stable from simple extrapolation of
periodic trends in the p-block. Further calculations on the stability
and electronic structure of BiH3, McH3, PoH2, and LvH2 are needed
before chemical investigations take place. Moscovium and livermorium
are expected to be volatile enough as pure elements for them to be
chemically investigated in the near future, a property livermorium
would then share with its lighter congener polonium, though the short
half-lives of all presently known livermorium isotopes means that the
element is still inaccessible to experimental chemistry.
External links
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* [
http://www.periodicvideos.com/videos/116.htm Livermorium] at 'The
Periodic Table of Videos' (University of Nottingham)
*
[
https://web.archive.org/web/20081205080201/http://www.cerncourier.com/main/article/41/8/17
'CERN Courier' - Second postcard from the island of stability]
* [
http://webelements.com/livermorium/ Livermorium at WebElements.com]
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=========
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Original Article:
http://en.wikipedia.org/wiki/Livermorium
