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Nuclear Theory·nucl-th

Thursday·November 5, 2015

9 papers—4 primary·5 cross-listed

All9Primary4Cross-lists5
  1. 01

    Fusion and quasi-fission dynamics in nearly-symmetric reactions

    Ning Wang · Kai Zhao · Zhuxia Li

    Some nearly-symmetric fusion reactions are systematically investigated with the improved quantum molecular dynamics (ImQMD) model. By introducing two-body inelastic scattering in the Fermi constraint procedure, the stability of an individual nucleus and the description of fusion cross sections at energies near the Coulomb barrier can be further improved. Simultaneously, the quasi-fission process in Sm+Gd is also investigated with the microscopic dynamics model for the first time. We find that at energies above the Bass barrier, the fusion probability is smaller than for this reaction, and the nuclear contact-time is generally smaller than fm/c. From the central collisions of Sm+Gd, the neutron-rich fragments such as Gd, W can be produced in the ImQMD simulations, which implies that the quasi-fission reaction could be an alternative way to synthesize new neutron-rich heavy nuclei.

    nucl-thSCPMA(2015)·13 citations
  2. 02

    Quark and gluon distribution functions in a viscous quark-gluon plasma medium and dilepton production via -- annihilation

    Vinod Chandra🇮🇳 · V. Sreekanth🇮🇳

    Viscous modifications to the thermal distributions of quark-antiquarks and gluons have been studied in a quasi-particle description of the quark-gluon-plasma medium created in relativistic heavy-ion collision experiments. The model is described in terms of quasi-partons that encode the hot QCD medium effects in their respective effective fugacities. Both shear and bulk viscosities have been taken in to account in the analysis and the modifications to thermal distributions have been obtained by modifying the the energy momentum tensor in view of the non-trivial dispersion relations for the gluons and quarks. The interactions encoded in the equation of state induce significant modifications to the thermal distributions. As an implication, dilepton production rate in the annihilation process has been investigated. The equation of state is found to have significant impact on the dilepton production rate along with the viscosities.

    nucl-thPRD(2015)·16 citations
  3. 03

    Neutron and spin--orbit splittings in Ca, S, and Si isotones: tensor--induced and pure spin--orbit effects

    M. Grasso🇫🇷 · M. Anguiano🇪🇸

    Neutron and spin--orbit splittings were recently measured in the isotones S and Si by transfer reactions. Values were reported by using the major fragments of the states. An important reduction of the splitting was observed, from S to Si, associated to a strong modification of the spin--orbit potential in the central region of the nucleus Si. We analyze and neutron spin--orbit splittings in the isotones Ca, S, and Si. We employ several Skyrme and Gogny interactions, to reliably isolate pure spin--orbit and tensor--induced contributions, within the mean--field approximation. We use interactions (i) without the tensor force; (ii) with the tensor force and with tensor parameters adjusted on top of existing parametrizations; (iii) with the tensor force and with tensor and spin--orbit parameters adjusted simultaneously on top of existing parametrizations. We predict in cases (ii) and (iii) a non negligible reduction of both and splittings, associated to neutron--proton tensor effects, from Ca to S. The two splittings are further decreased for the three types of interactions, going from S to Si. This reduction is produced by the spin--orbit force and is not affected by tensor--induced contributions. For both reductions, from Ca to S and from S to Si, we predict in all cases that the modification is more pronounced for than for splittings. The measurement of the centroids for neutron and states in the nuclei S and Si would be interesting to validate this prediction experimentally. We show the importance of using interactions of type (iii), because they provide and splittings in the nucleus Ca which are in agreement with the corresponding experimental values.

    nucl-thPRC(2015)·11 citations
  4. 04

    On microscopic theory of radiative nuclear reaction characteristics

    Sergei Kamerdzhiev · Oleg Achakovskiy · Alexander Avdeenkov · Stephane Goriely

    A survey of some results in the modern microscopic theory of properties of nuclear reactions with gamma-rays is given. First of all, we discuss the impact of phonon coupling (PC) on the photon strength function (PSF) because it represents the most natural physical source of additional strength found for Sn isotopes in recent experiments that could not be explained within the stan- dard HFB+QRPA approach. The self-consistent version of the Extended Theory of Finite Fermi Systems in the Quasiparticle Time Blocking Approximation, or simply QTBA, is applied. It uses the HFB mean field and includes both the QRPA and PC effects on the basis of the SLy4 Skyrme force. With our microscopic E1 PSFs, the following properties have been calculated for many stable and unstable even-even semi-magic Sn and Ni isotopes as well as for double-magic 132Sn and 208Pb using the reaction codes EMPIRE and TALYS with several nuclear level density (NLD) models: 1) the neutron capture cross sections, 2) the corresponding neutron capture gamma spectra, 3) the av- erage radiative widths of neutron resonances. In all the properties considered, the PC contribution turned out to be significant, as compared with the standard QRPA one, and necessary to explain the available experimental data. The results with the phenomenological so-called generalized super- fluid NLD model turned out to be worse, on the whole, than those obtained with the microscopic HFB+combinatorial NLD model. Finally, we also discuss the modern microscopic NLD models based on the self-consistent HFB method and show their relevance to explain experimental data as compared with the phenomeno- logical models. The use of these self-consistent microscopic approaches is of particular relevance for nuclear astrophysics, but also for the study of double-magic nuclei.

    nucl-thnucl-exPhys.Atom.Nucl.(2016)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE