Unbihexium

Unbihexium and Ubh are the temporary IUPAC name and symbol, respectively, until the element is discovered, confirmed, and a permanent name is decided upon.

[2] Early interest in possible increased stability led to the first attempted synthesis of unbihexium in 1971 and searches for it in nature in subsequent years.

Despite several reported observations, more recent studies suggest that these experiments were insufficiently sensitive; hence, no unbihexium has been found naturally or artificially.

Unbihexium is predicted to be a chemically active superactinide, exhibiting a variety of oxidation states from +1 to +8, and possibly being a heavier congener of plutonium.

[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.

[j] The first and only attempt to synthesize unbihexium, which was unsuccessful, was performed in 1971 at CERN (European Organization for Nuclear Research) by René Bimbot and John M. Alexander using the hot fusion reaction:[2][46] High-energy (13-15 MeV) alpha particles were observed and taken as possible evidence for the synthesis of unbihexium.

[47] A study in 1976 by a group of American researchers from several universities proposed that primordial superheavy elements, mainly livermorium, unbiquadium, unbihexium, and unbiseptium, with half-lives exceeding 500 million years[48] could be a cause of unexplained radiation damage (particularly radiohalos) in minerals.

A group led by Tom Cahill, a professor at the University of California at Davis, claimed in 1976 that they had detected alpha particles and X-rays with the right energies to cause the damage observed, supporting the presence of these elements, especially unbihexium.

[50] In particular, they cited that the magic number N = 228 necessary for enhanced stability would create a neutron-excessive nucleus in unbihexium that might not be beta-stable, although several calculations suggest that 354Ubh may indeed be stable against beta decay.

[51] This activity was also proposed to be caused by nuclear transmutations in natural cerium, raising further ambiguity upon this claimed observation of superheavy elements.

[52] Unbihexium has received particular attention in these investigations, for its speculated location in the island of stability may increase its abundance relative to other superheavy elements.

[48] Any naturally occurring unbihexium is predicted to be chemically similar to plutonium and may exist with primordial 244Pu in the rare earth mineral bastnäsite.

[55] A recent hypothesis tries to explain the spectrum of Przybylski's Star by naturally occurring flerovium, unbinilium, and unbihexium.

[56][57] Using the 1979 IUPAC recommendations, the element should be temporarily called unbihexium (symbol Ubh) until it is discovered, the discovery is confirmed, and a permanent name chosen.

[66] These reactions approached the limit of current technology; for example, the synthesis of tennessine required 22 milligrams of 249Bk and an intense 48Ca beam for six months.

[70] One calculation suggests that the cross section for producing unbihexium from 249Cf and 64Ni may be as low as nine orders of magnitude lower than the detection limit; such results are also suggested by the non-observation of unbinilium and unbibium in reactions with heavier projectiles and experimental cross section limits.

[2] This notion of an "island of stability" comprising longer-lived superheavy nuclei was popularized by University of California professor Glenn Seaborg in the 1960s.

[l] The extent of stabilizing effects in the region of unbihexium is uncertain, however, due to predictions of shifting or weakening of the proton shell closure and possible loss of double magicity.

Earlier models suggested the existence of long-lived nuclear isomers resistant to spontaneous fission in the region near 310Ubh, with half-lives on the order of millions or billions of years.

Instead, 310Ubh is thought to be very neutron-deficient and susceptible to alpha decay and spontaneous fission in less than a microsecond, and it may even lie at or beyond the proton drip line.

[80] This study and a quantum tunneling model predict alpha-decay half-lives under a microsecond for isotopes lighter than 318Ubh, rendering them impossible to identify experimentally.

As with the other early superactinides, it is predicted that unbihexium will be able to lose all eight valence electrons in chemical reactions, rendering a variety of oxidation states up to +8 possible.

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 ]
This nuclear chart used by the Japan Atomic Energy Agency predicts the decay modes of nuclei up to Z = 149 and N = 256. At Z = 126 (top right), the beta-stability line passes through a region of instability towards spontaneous fission (half-lives less than 1 nanosecond ) and extends into a "cape" of stability near the N = 228 shell closure, where an island of stability centered at the possibly doubly magic isotope 354 Ubh may exist. [ 74 ]
This diagram depicts shell gaps in the nuclear shell model. Shell gaps are created when more energy is required to reach the shell at the next higher energy level, thus resulting in a particularly stable configuration. For protons, the shell gap at Z = 82 corresponds to the peak of stability at lead, and while there is disagreement of the magicity of Z = 114 and Z = 120, a shell gap appears at Z = 126, thus suggesting that there may be a proton shell closure at unbihexium. [ 75 ]