Isotopes of livermorium

The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 116.

In 1995, the team at GSI attempted the synthesis of ²⁹⁰Lv as a radiative capture (x=0) product. No atoms were detected during a six-week experimental run, reaching a cross section limit of 3 pb.^[8]

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.

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.^[9]

In 2023, this reaction was studied again at the JINR's Superheavy Element Factory in Dubna, in preparation for a future synthesis attempt of element 120 using ⁵⁴Cr projectiles. One atom of ²⁸⁸Lv was reported; it underwent alpha decay with a lifetime of less than 1 millisecond.^[10] The cross-section was measured as 36+46
−24 fb for the 4n channel.^[5]

In 2024, this reaction was performed at the LBNL, in preparation for a future synthesis attempt of element 120 using ⁵⁰Ti projectiles. Two atoms of the known isotope ²⁹⁰Lv were successfully produced.^[11][12][13] This was the first successful synthesis of a superheavy element using ⁵⁰Ti projectiles and an actinide target; the cross-section was reported to be 0.44+0.58
−0.28 pb.^[14]

In 2024, this reaction was studied at the JINR, as a next step after the successful ²³⁸U+⁵⁴Cr reaction. Two atoms of ²⁸⁸Lv were detected, as well as three atoms of the new alpha-decaying isotope ²⁸⁹Lv. One atom of ²⁸⁹Mc was found in the p2n channel, which was the first time any pxn channel had been detected in a reaction of actinides with ⁴⁸Ca, ⁵⁰Ti, or ⁵⁴Cr projectiles.^[6] The cross-section was reported to be 320+340
−180 fb for the 3n channel, and 220+270
−150 fb for the 4n channel.^[5]

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.^[15] Yuri Oganessian and his team at the Flerov Laboratory of Nuclear Reactions (FLNR) subsequently attempted the reaction in 1978 and met 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.^[16]

In 2000, Russian scientists at Dubna finally succeeded in detecting a single atom of livermorium, assigned to the isotope ²⁹²Lv.^[17] 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.^[18] 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 or an isomer, ^293mLv; given the possible reassignment of its daughter to ²⁹⁰Fl instead of ²⁸⁹Fl, it could also conceivably be ²⁹⁴Lv, although all these assignments are tentative and need confirmation in future experiments aimed at the 2n channel.^[19][20] In this reaction, two additional atoms of ²⁹³Lv were detected.^[21]

In 2007, in a GSI-SHIP experiment, besides four ²⁹²Lv chains and one ²⁹³Lv chain, another chain was observed, initially not assigned but later shown to be ²⁹¹Lv. However, it is unclear whether it comes from the ²⁴⁸Cm(⁴⁸Ca,5n) reaction or from a reaction with a lighter curium isotope (present in the target as an admixture), such as ²⁴⁶Cm(⁴⁸Ca,3n).^[22][23]

In an experiment run at the GSI during June–July 2010, scientists detected six atoms of livermorium; two atoms of ²⁹³Lv and four atoms of ²⁹²Lv. They were able to confirm both the decay data and cross sections for the fusion reaction.^[24]

A 2016 experiment at RIKEN aimed at studying the ⁴⁸Ca+²⁴⁸Cm reaction seemingly detected one atom that may be assigned to ²⁹⁴Lv alpha decaying to ²⁹⁰Fl and ²⁸⁶Cn, which underwent spontaneous fission; however, the first alpha from the livermorium nuclide produced was missed.^[7]

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.^[25] This experiment was successfully repeated in February–March 2005 where 10 atoms were created with identical decay data to those reported in the 2003 experiment.^[26]

Livermorium has also been observed in the decay of oganesson. In October 2006 it was announced that three atoms of oganesson had been detected by the bombardment of californium-249 with calcium-48 ions, which then rapidly decayed into livermorium.^[26]

The observation of the daughter ²⁹⁰Lv allowed the assignment of the parent to ²⁹⁴Og and confirmed the synthesis of oganesson.

Several experiments have been performed between 2000 and 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 roughly three times smaller for ⁵⁰Ti, also suggesting a future use in SHE production.^[27]

In 1999, researchers at Lawrence Berkeley National Laboratory announced the synthesis of ²⁹³Og (see oganesson), in a paper published in Physical Review Letters.^[28] 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.^[29] 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. This isotope of livermorium was finally discovered in 2024 by the JINR, in the ²⁴²Pu(⁵⁰Ti,3n) reaction.^[6]

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. + represents an observed exit channel.

Theoretical calculation in a quantum tunneling model supports the experimental data relating to the synthesis of ²⁹³Lv and ²⁹²Lv.^[30][31]

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