Element 112 was discovered in 1996. It should be a heavy homolog of the elements mercury, cadmium, and zinc, and is expected to be the last element in the 6d shell. See also: Cadmium; Half-life; Mercury (element); Zinc
A long-standing claim to having synthesized element 112 is made by a Jerusalem-European Organization for Nuclear Research (CERN) collaboration. A spontaneous fission emitter with a half-life of several weeks was found in 1971 in a tungsten-beam stop at CERN. It followed the chemistry of mercury, and was assigned to element 112. A two-step reaction mechanism was proposed. From the tungsten-beam stop of the 24-GeV particle accelerator strontium-88 is produced by high-energy fission of fissionable spallation products. In a second reaction the 88Sr ions induce a fusion reaction with another tungsten nucleus. The nucleus 272112 (the isotope of element 112) is synthesized at very low excitation energy by radiative capture and is detected after chemical separation by its fission. See also: Nuclear reaction; Spallation reaction; Strontium; Tungsten
Element 112 was discovered on February 9, 1996, at GSI (Gesellschaft für Schwerionenforschung), Darmstadt, Germany, by detection of 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. The fused system was observed at an excitation energy of 12 MeV. Sequential alpha decays to darmstadtium-273, 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 0.7 ms, and it is produced with a cross section of 0.5 × 10−37 cm2. The new isotopes of darmstadtium and hassium are of special interest. Their half-lives differ by more than four orders of magnitude, and alpha energies are very different, which is characteristic of a closed-shell crossing. At the neutron number N = 162, a closed shell was theoretically predicted, and this 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: Alpha particles; Darmstadtium; Hassium; Lead; Neutron; Nobelium; Nuclear structure; Radioisotope; Rutherfordium; Seaborgium
The methods used to produce element 112 were the same as those used for darmstadtium and roentgenium. The decay chain of the new element was observed in an irradiation time of about 3 weeks. The trend toward smaller cross sections has continued. See also: Roentgenium
In May 2000, a decay chain of 277112 was detected by the GSI group, ending by spontaneous fission decay. In 2004, two more decay chains ending by spontaneous fission of 261Rf were found at RIKEN, Japan. The decay chain of 277112 feeds the isotope 269Hs, which was produced in the reaction 248Cm(26Mg,5n) by the GSI nuclear chemistry group in 2003. The decay chains observed confirm the pattern of isotopes from 277112.
Theoretical model calculations of the element 112 chemistry indicate that it may exhibit rather unusual properties. On the basis of its projected position in group 12 of the periodic table it should behave like a heavy metal similar to its homolog mercury (atomic number 80). However, it is predicted that an extra stabilization of its binding electrons may result in a relatively high volatility, giving rise to some similarity with the noble gas radon (atomic number 86). See also: Radon