Unbiunium

Unbiunium and Ubu are the temporary systematic IUPAC name and symbol respectively, which are used until the element is discovered, confirmed, and a permanent name is decided upon.

[14] The definition by the IUPAC/IUPAP Joint Working Party (JWP) states that a chemical element can only be recognized as discovered if a nucleus of it has not decayed within 10−14 seconds.

This value was chosen as an estimate of how long it takes a nucleus to acquire electrons and thus display its chemical properties.

However, its range is very short; as nuclei become larger, its influence on the outermost nucleons (protons and neutrons) weakens.

In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets (actinides), giving rise to compound nuclei at high excitation energies (~40–50 MeV) that may fission or evaporate several (3 to 5) neutrons.

[48] In cold fusion reactions (which use heavier projectiles, typically from the fourth period, and lighter targets, usually lead and bismuth), the fused nuclei produced have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions.

[49] Attempts to synthesize elements 119 and 120 push the limits of current technology, due to the decreasing cross sections of the production reactions and their probably short half-lives,[46] expected to be on the order of microseconds.

[46] Where this one-microsecond border of half-lives lies is not known, and this may allow the synthesis of some isotopes of elements 121 through 124, with the exact limit depending on the model chosen for predicting nuclide masses.

[53] The synthesis of unbiunium was first attempted in 1977 by bombarding a target of uranium-238 with copper-65 ions at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany: No atoms were identified.

[46] The multiplicity of excited states populated by the alpha decay of odd nuclei may however preclude clear cross-bombardment cases, as was seen in the controversial link between 293Ts and 289Mc.

[58][63][64] These two laboratories are best suited to these experiments as they are the only ones in the world where long beam times are accessible for reactions with such low predicted cross-sections.

Using the 1979 IUPAC recommendations, the element should be temporarily called unbiunium (symbol Ubu) until it is discovered, the discovery is confirmed, and a permanent name chosen.

[68][69] In fact, the very existence of elements heavier than rutherfordium can be attested to shell effects and the island of stability, as spontaneous fission would rapidly cause such nuclei to disintegrate in a model neglecting such factors.

Only the isotopes from 309Ubu to 314Ubu would have long enough alpha-decay lifetimes to be detected in laboratories, starting decay chains terminating in spontaneous fission at moscovium, tennessine, or ununennium.

[71] Calculations in 2016 and 2017 by the same authors on elements 123 and 125 suggest a less bleak outcome, with alpha decay chains from the more reachable nuclides 300–307Ubt passing through unbiunium and leading down to bohrium or nihonium.

[73][74][75] Unbiunium is predicted to be the first element of an unprecedentedly long transition series, called the superactinides in analogy to the earlier actinides.

[76][1] Based on the Aufbau principle, one would expect the 5g subshell to begin filling at the unbiunium atom.

It is predicted that a similar situation of delayed "radial" collapse might happen for unbiunium so that the 5g orbitals do not start filling until around element 125, even though some 5g chemical involvement may begin earlier.

[78] Unbiunium is expected to fill the 8p1/2 orbital due to its relativistic stabilization, with a configuration of [Og] 8s2 8p1.

A similar large reduction in ionization energy is also seen in lawrencium, another element having an anomalous s2p configuration due to relativistic effects.

[1] Despite the change in electron configuration and possibility of using the 5g shell, unbiunium is not expected to behave chemically very differently from lanthanum and actinium.

Unbiunium may hence be somewhat like lawrencium in having an anomalous s2p configuration that does not affect its chemistry: the bond dissociation energies, bond lengths, and polarizabilities of the UbuF molecule are expected to continue the trend through scandium, yttrium, lanthanum, and actinium, all of which have three valence electrons above a noble gas core.

[1][2][77] Relativistic effects appear to be small for the unbiunium trihalides, with UbuBr3 and LaBr3 having very similar bonding, though the former should be more ionic.

A graphic depiction of a nuclear fusion reaction
A graphic depiction of a nuclear fusion reaction. Two nuclei fuse into one, emitting a neutron . Reactions that created new elements to this moment were similar, with the only possible difference that several singular neutrons sometimes were released, or none at all.
Apparatus for creation of superheavy elements
Scheme of an apparatus for creation of superheavy elements, based on the Dubna Gas-Filled Recoil Separator set up in the Flerov Laboratory of Nuclear Reactions in JINR. The trajectory within the detector and the beam focusing apparatus changes because of a dipole magnet in the former and quadrupole magnets in the latter. [ 29 ]
A 2D graph with rectangular cells colored in black-and-white colors, spanning from the llc to the urc, with cells mostly becoming lighter closer to the latter
Chart of nuclide stability as used by the Dubna team in 2010. Characterized isotopes are shown with borders. Beyond element 118 (oganesson, the last known element), the line of known nuclides is expected to rapidly enter a region of instability, with no half-lives over one microsecond after element 121. The elliptical region encloses the predicted location of the island of stability. [ 46 ]
Predicted decay modes of superheavy nuclei. The line of synthesized proton-rich nuclei is expected to be broken soon after Z = 120, because of the shortening half-lives until around Z = 124, the increasing contribution of spontaneous fission instead of alpha decay from Z = 122 onward until it dominates from Z = 125, and the proton drip line around Z = 130. Beyond this is a region of slightly increased stability of second-living nuclides around Z = 124 and N = 198, but it is separated from the mainland of nuclides that may be obtained with current techniques. The white ring denotes the expected location of the island of stability; the two squares outlined in white denote 291 Cn and 293 Cn, predicted to be the longest-lived nuclides on the island with half-lives of centuries or millennia. [ 55 ] [ 50 ]