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Sample records for 256no 270sg 271hs

  1. Chemical studies of elements with Z ⩾ 104 in gas phase

    Türler, Andreas; Eichler, Robert; Yakushev, Alexander

    2015-12-01

    Chemical investigations of superheavy elements in the gas-phase, i.e. elements with Z ≥ 104, allow assessing the influence of relativistic effects on their chemical properties. Furthermore, for some superheavy elements and their compounds quite unique gas-phase chemical properties were predicted. The experimental verification of these properties yields supporting evidence for a firm assignment of the atomic number. Prominent examples are the high volatility observed for HsO4 or the very weak interaction of Cn with gold surfaces. The unique properties of HsO4 were exploited to discover the doubly-magic even-even nucleus 270Hs and the new isotope 271Hs. The combination of kinematic pre-separation and gas-phase chemistry allowed gaining access to a new class of relatively fragile compounds, the carbonyl complexes of elements Sg through Mt. A not yet resolved issue concerns the interaction of Fl with gold surfaces. While competing experiments agree on the fact that Fl is a volatile element, there are discrepancies concerning its adsorption on gold surfaces with respect to its daughter Cn. The elucidation of these and other questions amounts to the fascination that gas-phase chemical investigations exert on current research at the extreme limits of chemistry today.

  2. Role of mass asymmetry in fusion of super-heavy nuclei

    By using well tested standard statistical model for calculating survival probabilities of super-heavy compound nuclei, Psurv, and reliably predicted capture cross sections σcap, “empirical” values of the fusion hindrance Pfus = σsyn/(σcap · Psurv) have been determined from the formation cross sections σsyn for production of super-heavy nuclei of 102 ≤ Z ≤ 113 measured at GSI Darmstadt and RIKEN. So determined fusion hindrance can be well reproduced with a simple model based on the Smoluchowski diffusion equation applied to describe thermal shape fluctuations of the fusing system. An applicability of this model for a wider class of fusing systems could be verified on data from an interesting experiment on the synthesis of isotopes of Hs (Z = 108) in the 136Xe + 136Xe reaction, scheduled to be carried out in Dubna this year. Synthesis cross sections for 269-271Hs isotopes, strongly reduced by the fusion hindrance effect in this symmetric fusion reaction, are predicted. (author)

  3. Production of Hs-isotopes (Z=108) in the reaction 26Mg+248Cm

    Chemical studies of superheavy elements (SHE) are most convincing if, after chemical isolation, a nuclide is unambiguously identified by its nuclear decay properties. Thus chemists contribute not only new data on chemical properties of SHE but also nuclear structure information. Since chemists usually work with neutron-rich, longer-lived isotopes of SHE which are accessible only in asymmetric reactions with actinide targets and thus hard to access with recoil separators, this contribution is especially valuable. We have used the so-called In-situ Volatilization and On-line detection (IVO) technique to study the excitation function of the reaction 248Cm(26Mg,xn)274-xHs (x-5) thereby measuring the decay properties of the new nuclide 270Hs and its daughter 266Sg. It appears as if in earlier experiments our tentative assignment of two decay chains to 270Hs was not correct. This assignment was based on the decay properties of 266Sg reported by Lazarev et al., where the discovery of265Sg and 266Sg was described. Our new data indicates now, that due to an isomeric state in 261Rf which decays mostly by spontaneous fission, two decay chains tentatively assigned earlier to 270Hs and 266Sg are actually due to 269Hs and 265Sg. In addition, we observed several decay chains which were tentatively assigned to 271Hs and its decay daughters. The measured cross sections are of the order of few picobarns. Prospects to apply the IVO technique to other nuclides of SHE will be discussed. In addition, an overview about the status of the gas-filled separator TASCA (TransActinide Separator and Chemistry Apparatus) which is currently under construction at Gesellschaft fuer Schwerionenforschung (GSI) will be presented

  4. Decay properties of nuclei close to Z = 108 and N = 162

    The goal of the research conducted in the frame of this thesis was to investigate the decay properties of the nuclides 269-271Hs and their daughters using an improved chemical separation and detection system. Shell stabilization was predicted in the region around Z=108 and N=162 in calculations, taking into account possible higher orders of deformations of the nuclei. The nucleus 270Hs with a closed proton and a closed neutron deformed shell, was predicted to be ''deformed doubly magic''. Nuclei around 270Hs can be produced only via fusion reactions at picobarn levels, resulting in a production rates of few atoms per day. Investigating short-lived nuclei using rapid chemical separation and subsequent on-line detection methods provides an independent and alternative means to electromagnetic on-line separators. Chemical separation of Hs in the form of HsO4 provides an excellent tool to study the formation reactions and nuclear structure in this region of the chart of nuclides due to a high overall efficiency and a very high purification factor. The goal was accomplished, as element 108, hassium, was produced in the reaction 248Cm(26Mg,xn)274-xHs and chemically isolated. After gas phase separation of HsO4, 26 genetically linked decay chains have been observed. These were attributed to decays of three different Hs isotopes produced in the 3-5n evaporation channels. The known decay chain of 269Hs, the 5n evaporation product, serves as an anchor point, thus allowing the unambiguous assignment of the observed decay chains to the 5n, 4n, and 3n channels, respectively. Decay properties of five nuclei have been unambiguously established for the first time, including the one for the the doubly-magic nuclide 270Hs. This hassium isotope is the next doubly magic nucleus after the well known 208Pb and the first experimentally observed even-even nucleus on the predicted N=162 neutron shell. The observed decay properties provide strong indications for enhanced nuclear stability in

  5. Reaction 48Ca+208Pb: the capture-fission cross-sections and the mass-energy distributions of fragments above and deep below the Coulomb barrier

    Prokhorova, E. V.; Cherepanov, E. A.; Itkis, M.G.; Kondratiev, N. A.; Kozulin, E. M.; Krupa, L.; Oganessian, Yu.Ts.; Pashkevich, V. V.; Pokrovsky, I. V.; Rusanov, A. Ya.

    2003-01-01

    The capture-fission cross-sections in an energy range of 206-242 MeV of 48Ca-projectiles and mass-energy distributions (MEDs) of reaction products in an energy range of 211-242 MeV have been measured in the 48Ca+208Pb reaction using the double-arm time-of-flight spectrometer CORSET. The MEDs of fragments for heated fission were shown to consist of two components. One component, which is due to classical fusion-fission, is associated with the symmetric fission of the 256No compound nucleus. Th...

  6. Redes booleanas como modelos discretos da realidade

    Freitas, José António Fernandes de

    2010-01-01

    É conhecido que, no caso dos autómatos celulares elementares unidimensionais, o espaço das regras possui cardinalidade 256. No entanto, rapidamente se observou que, na realidade, este espaço podia ser reduzido devido à introdução de certas transformações de equivalência dinâmica. O número de regras não equivalentes, isto é, o número de classes de equivalência de regras, passa então para apenas 88. Motivados por estas pesquisas, começamos por estudar as diferentes transformações dinamica...

  7. The fusion fission and quasi-fission processes in the reaction 48Ca + 208Pb at energies near the Coulomb barrier

    Prokhorova, E. V.; Bogachev, A. A.; Itkis, M. G.; Itkis, I. M.; Knyazheva, G. N.; Kondratiev, N. A.; Kozulin, E. M.; Krupa, L.; Oganessian, Yu. Ts.; Pokrovsky, I. V.; Pashkevich, V. V.; Rusanov, A. Ya.

    2008-04-01

    Mass-energy distributions (MEDs) and capture-fission cross sections have been measured in the reaction 48Ca + 208Pb → 256No at the energies E=206-242 MeV using a double-arm time-of-flight spectrometer CORSET. It has been observed that MED of the fragments consists of two parts, namely, the classical fusion-fission process corresponding to the symmetric fission of 256No and quasi-fission "shoulders" corresponding to the light fragment masses ˜60-90 u and complimentary heavy fragment masses. The quasi-fission "shoulders" have a higher total kinetic energy (TKE) as compared with that expected for the classical fission. A mathematical formalism was employed for the MEDs fragment decomposition into fusion-fission and quasi-fission components. In the fusion-fission process a high-energy Super-Short mode has been discovered for the masses M=130-135 u and the TKE of ≈233 MeV.

  8. The fusion-fission and quasi-fission processes in the reaction 48Ca + 208Pb at energies near the Coulomb barrier

    Mass-energy distributions (MEDs) and capture-fission cross sections have been measured in the reaction 48Ca + 208Pb →256No at the energies Elab=206-242 MeV using a double-arm time-of-flight spectrometer CORSET. It has been observed that MED of the fragments consists of two parts, namely, the classical fusion-fission process corresponding to the symmetric fission of 256No and quasi-fission 'shoulders' corresponding to the light fragment masses ∼60-90 u and complimentary heavy fragment masses. The quasi-fission 'shoulders' have a higher total kinetic energy (TKE) as compared with that expected for the classical fission. A mathematical formalism was employed for the MEDs fragment decomposition into fusion-fission and quasi-fission components. In the fusion-fission process a high-energy Super-Short mode has been discovered for the masses MH=130-135 u and the TKE of ∼233 MeV

  9. Theory of competition between fusion and quasi-fission in a heavy fusing system

    Díaz-Torres, A

    2006-01-01

    A theory of the competition between fusion and quasi-fission in a heavy fusing system is proposed, which is based on a master equation and the two-center shell model. Fusion and quasi-fission arise from a diffusion process in an ensemble of nuclear shapes evolving towards the thermal equilibrium. The master equation describes the diffusion of the nuclear shapes due to quantum and thermal fluctuations. Other crucial physical effects like dissipation, ground-state shell effects, diabatic effects and rotational effects are also incorporated into the theory. The fusing system moves in a dynamical (time-dependent) collective potential energy surface which is initially diabatic and gradually becomes adiabatic. The microscopic ingredients of the theory are obtained with a realistic two-center shell model based on Woods-Saxon potentials. Numerical calculations for several reactions leading to $^{256}$No are discussed. Among other important conclusions, the results indicate that (i) the diabatic effects play a very im...

  10. Dynamical collective potential energy landscape: its impact on the competition between fusion and quasi-fission in a heavy fusing system

    Díaz-Torres, A

    2006-01-01

    A realistic microscopically-based quantum approach to the competition between fusion and quasi-fission in a heavy fusing system is applied to several reactions leading to $^{256}$No. Fusion and quasi-fission are described in terms of a diffusion process of nuclear shapes through a dynamical collective potential energy landscape which is initially diabatic and gradually becomes adiabatic. The microscopic ingredients of the theory are obtained with a realistic two-center shell model based on Woods-Saxon potentials. The results indicate that (i) the diabatic effects play a very important role in the onset of fusion hindrance for heavy systems, and (ii) very asymmetric reactions induced by closed shell nuclei seem to be the best suited to synthesize the heaviest compound nuclei.

  11. Role of the second barrier upon mass division in the spontaneous fission of the heaviest elements

    In the region where theorists had earlier predicted the disappearance of the outer fission barrier or of it dropping below the ground-state, we have measured the mass and total-kinetic-energy distributions from spontaneous fission of 252No, 254No, 256[104], and 258[104]. The results, in combination with earlier measurements for 256No, 258No, and 262No, show a sharp transition from asymmetrical mass division in 256No to symmetrical ones for 258No and 262No. On-the-other-hand, all isotopes of element 104 including 260[104] appear to yield broadly symmetrical mass distributions. The total-kinetic energies around 200 MeV for the 104 isotopes indicate they fission by the low-energy mode of bimodal fission. Based on the hypothesis that the second barrier is responsible for asymmetrical mass distributions and when it disappears, for symmetrical ones, these observations for the isotopes of element 104 are in accord with 1976 calculations of the heights of the second fission barrier relative to the ground-state. Some recent calculations of static potential-energy surfaces and of barrier heights deduced from half-lives for spontaneous fission indicate the second barrier is from 0 to 2.9 MeV above the ground-state for the No and 104 isotopes. However, shape degrees-of-freedom have been limited in these calculations so that they fail to provide realistic heights for the outer fission barrier. For the few cases where higher-order asymmetrical deformations are included, this barrier height is well below the ground-state and, for these nuclides, we observe symmetric mass division only. Without more extensive calculations of potential-energy surfaces for comparison with our findings, we are unable reach a firm conclusion on the role of the second barrier upon mass division in fission

  12. Is baby-friendly breastfeeding support in maternity hospitals associated with breastfeeding satisfaction among Japanese mothers?

    Hongo, Hiroko; Nanishi, Keiko; Shibanuma, Akira; Jimba, Masamine

    2015-06-01

    While the World Health Organization's Baby-Friendly Hospital Initiative has increased breastfeeding duration and exclusivity, a survey found that only 8.5 % of maternity hospitals in 31 developed countries could be designated baby-friendly. Baby-friendly breastfeeding support is sometimes criticized as mother unfriendly. This study examined whether baby-friendly breastfeeding support was associated with breastfeeding satisfaction, duration, and exclusivity among Japanese mothers. In this cross-sectional study, 601 breastfeeding Japanese mothers completed questionnaires at their infants' 4-month health checkups at two wards in Yokohama, Japan; 363 were included in the analysis. Baby-friendly breastfeeding support was measured based on the WHO's "Ten Steps to Successful Breastfeeding." We measured satisfaction using two subscales of the Japanese version of the Maternal Breastfeeding Evaluation Scale. The association of baby-friendly support with maternal satisfaction was assessed using multiple linear regression, while the prevalence ratios (PRs) for breastfeeding were estimated using Poisson regression. Mothers were stratified by prepartum exclusive breastfeeding intention (yes, n = 256; no, n = 107). Mothers who experienced early skin-to-skin contact with their infants were more likely to report breastfeeding satisfaction than those who did not. Among mothers without exclusive breastfeeding intention, those who were encouraged to feed on demand were more likely to be breastfeeding without formula at 1 month (PR 2.66 [95 % CI 1.32, 5.36]) and to perceive breastfeeding as beneficial for their baby (regression coefficient = 3.14 [95 % CI 0.11, 6.17]) than those who were not so encouraged. Breastfeeding satisfaction was a useful measure of breastfeeding outcome. Early skin-to-skin contact and encouragement to feed on demand in the hospital facilitate breastfeeding satisfaction. PMID:25366103