Chemical identification and properties of element 112

Abstract

The second experiment on the chemical identification of element 112 performed at the FLNR (Dubna) is reported. Similar to the first test in 2000, the 2 mg/cm sup 2 sup n sup a sup t U target was bombarded with the 262-MeV sup 4 sup 8 Ca ions aiming at the production of sup 2 sup 8 sup 3 112, which as reported earlier decays by SF with a half-life of 3 min. The bombardment products recoiling from the target were thermalized in flowing helium and transported by the gas to detectors 25 m apart. Of all the heavy elements, the reaction products, only Hg, Rn and At were efficiently transported and thus selectively isolated. This time the beam dose was much higher (2.8 centre dot 10 sup 1 sup 8) and two different devices for detecting fission fragments and alpha particles were employed. The device used earlier was an assembly of sixteen PIPS detectors coated with Au to detect 'Hg-like' nuclides being adsorbed on Au at ambient temperature. The new one was a flow-through ionization chamber, 5000 cm sup 3 in volume, which served for detecting the activities still remaining in the gas after passing through the PIPS detector channel. Both devices were placed into an assembly of 126 neutron counters to detect prompt fission neutrons. In 22.5 days of the bombardment, eight fission events in coincidence with neutrons were observed, all of them in the ionization chamber, while only one background count could be expected during that time. Hence, most of the observed decays can be attributed to element 112. The simultaneously produced 49-s alpha-active sup 1 sup 8 sup 5 Hg was completely deposited on the first PIPS detector. The values of adsorption enthalpy calculated from the experimental data confirm that the interaction of element 112 with the Au surface is much weaker than that of Hg. These facts point to the 'Rn-like' rather than 'Hg-like' behavior of element 112 in the given chemical environment. A production cross section of about 2 pb was evaluated for the nuclide unde