element 112

n.
An artificially produced radioactive element with atomic number 112 whose isotope has a mass number of 277 and a half-life of 280 milliseconds. Also called ununbium.

Element 112 was discovered in 1996. It should be a heavy homolog of the elements mercury, cadmium, and zinc. It is expected to be the last element in the 6d shell. No chemistry is possible in the near future as all cross sections are in the range of 10⁻³⁶ cm² and the half-lives are short. See also Cadmium; Half-life; Periodic table; Zinc.

Element 112 was discovered on February 9, 1996, at GSI (Gesellschaft für Schwerionenforschung), Darmstadt, Germany, by detection of the isotope ²⁷⁷112, which was produced by fusion of a zinc-70 projectile and a lead-208 target nucleus following the cooling down of the fused system by emission of a single neutron. Sequential alpha decays to ²⁷³110, hassium-269, seaborgium-265, rutherfordium-261, and nobelium-257 allowed unambiguous identification by using the known decay properties of the last three members of the chain. In the decay chain (see illustration), the first three members are new isotopes. Isotope ²⁷⁷112 has a half-life of 0.24 ms, and it is produced with a cross section of 1.0 × 10⁻³⁶ cm² (the smallest observed in the production of heavy elements). The new isotopes of darmstadtium and hassium are of special interest. Their half-lives and alpha energies are very different, as is characteristic of a closed-shell crossing. At the neutron number N = 162, a closed shell was theoretically predicted, and this closed shell is verified in the decay chain observed. Isotope ²⁶⁹Hs has a half-life of 9 s, which is long enough to allow studies on the chemistry of this element. The crossing of the neutron shell at N = 162 is an important achievement in the field of research on superheavy elements. The stabilization of superheavy elements is based on high fission barriers, which are due to corrections in the binding energies found near closed shells. The shell at N = 162 is the first such shell predicted, and is now verified. See also Darmstadtium; Element 111; Hassium; Lead; Neutron; Nobelium; Rutherfordium; Seaborgium.

Sequence of decay chains that document the discovery of element 112. Numbers below boxes are alpha energies and correlation times. Element 112 is produced in the reaction ⁷⁰Zn + ²⁰⁸Pb → ²⁷⁷112 + 1n.

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