Starting from a lead ore having an age of 1.3 x 10 9 years, an already chemically pre-enriched material up to a factor of about 2 to 3 x 10 8 was available for the search of the element 114 based on the properties predicted for eka lead. A further physical enrichment was undertaken using the Juelich high performance electromagnetic isotope separator. The exposed target material (synthetic quartz glass plates)in the mass range 278 to 290 in the mass separator was irradiated with thermal neutrons and the fission tracks were counted under an optical microscope. The background due to fissionable impurities in the quartz ( -13 atoms per SiO 2 molecule) and that due to the use of the mass separator were studied in preliminary experiments. The possible escape of the presumably volatile element 114 from the fission track detectors during irradiation as a result of nuclear γ-heating was also investigated in simulation experiments. The diffusion behaviour of carrier-free 203 Hg implanted into quartz plates in the mass separator, as determined by a radiometric analysis, showed that the expected losses are negligible below 200 0 C. The counting results from the fission track detectors gave a maximum value of 5.1 x 10 -22 barns for the product of the fission cross section sigmasub(f) and the number of eka-lead atoms per lead carrier atom. In order to be able to make an estimate of the absolute concentration limits, the fission cross sections of eka-lead for thermal neutrons were approximated using an extrapolation method. Assuming these approximate fission cross sections, the absolute concentration limits of 8 x 10sup(-24), 3 x 10 -22 and 1 x 10 -19 share of eka-lead atoms per carrier atom were obtained for the isotopes 295, 297 and 298 (sigma = 70 barns, 2 barns and 4 gbarns). (orig./LH) [de
Wittwer, D.; Abdullin, F.Sh.; Aksenov, N.V.; Albin, Yu.V.; Bozhikov, G.A.; Dmitriev, S.N.; Dressler, R.; Eichler, R.; Gaeggeler, H.W.; Henderson, R.A.; Huebener, S.; Kenneally, J.M.; Lebedev, V.Ya.; Lobanov, Yu.V.; Moody, K.J.; Oganessian, Yu.Ts.; Petrushkin, O.V.; Polyakov, A.N.; Piguet, D.; Rasmussen, P.
Currently, gas phase chemistry experiments with heaviest elements are usually performed with the gas-jet technique with the disadvantage that all reaction products are collected in a gas-filled thermalisation chamber adjacent to the target. The incorporation of a physical preseparation device between target and collection chamber opens up the perspective to perform new chemical studies. But this approach requires detailed knowledge of the stopping force (STF) of the heaviest elements in various materials. Measurements of the energy loss of mercury (Hg), radon (Rn), and nobelium (No) in Mylar and argon (Ar) were performed at low kinetic energies of around (40-270) keV per nucleon. The experimentally obtained values were compared with STF calculations of the commonly used program for calculating stopping and ranges of ions in matter (SRIM). Using the obtained data points an extrapolation of the STF up to element 114, eka-lead, in the same stopping media was carried out. These estimations were applied to design and to perform a first chemical experiment with a superheavy element behind a physical preseparator using the nuclear fusion reaction 244 Pu( 48 Ca; 3n) 289 114. One decay chain assigned to an atom of 285 112, the α-decay product of 289 114, was observed.