Livermorium

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; about 35 livermorium atoms had been made . 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. 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 beginning in 1990, production of more intense ⁴⁸Ca beams beginning 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

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. 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.

: + → * → + 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, 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. 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. 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.

Naming

thumb|upright|[[Robert Livermore, the indirect namesake of livermorium]]

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. The discovery of livermorium was recognized by the Joint Working Party (JWP) of IUPAC on 1 June 2011, along with that of flerovium. 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.

Other routes of synthesis

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. 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 (two new chains) and discovering the new isotope ²⁸⁹Lv (three chains). and the fact that it decays very quickly. Properties of livermorium remain unknown and only predictions are available.

Nuclear stability and isotopes

right|thumb|upright=1.8|The expected location of the island of stability is marked by the white circle. The dotted line is the line of [[beta decay|beta stability.]]

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. 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 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. 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. 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. 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 7p_1/2 subshell acts as a second inert pair, though not as inert as the 7s electrons, while the 7p_3/2 subshell can easily participate in chemistry. 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. 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

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.

Notes

References

Bibliography

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External links

• Livermorium at The Periodic Table of Videos (University of Nottingham)
• CERN Courier – Second postcard from the island of stability
• Livermorium at WebElements.com