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Nuclear Theory·nucl-th

Wednesday·March 14, 2018

7 papers—4 primary·3 cross-listed

All7Primary4Cross-lists3
  1. 01

    [Submitted on 13 Mar 2018]

    Calculation of multidimensional potential energy surfaces for even-even transuranium nuclei: Systematic investigation of the triaxiality effect on fission barrier

    Qing-Zhen Chai · Wei-Juan Zhao · Min-Liang Liu · Hua-Lei Wang

    Static fission barriers for 95 even-even transuranium nuclei with charge number have been systematically investigated by means of pairing self-consistent Woods-Saxon-Strutinsky calculations using the potential energy surface approach in multidimensional (, , ) deformation space. Taking the heavier Cf nucleus (with the available fission barrier from experiment) as an example, the formation of the fission barrier and the influence of macroscopic, shell and pairing correction energies on it are analyzed. The results of the present calculated values and barrier heights are compared with previous calculations and available experiments. The role of triaxiality in the region of the first saddle is discussed. It is found that the second fission barrier is also considerably affected by the triaxial deformation degree of freedom in some nuclei (e.g., the isotopes). Based on the potential energy curves, general trends of the evolution of the fission barrier heights and widths as a function of the nucleon numbers are investigated. In addition, the effects of Woods-Saxon potential parameter modifications (e.g., the strength of the spin-orbit coupling and the nuclear surface diffuseness) on the fission barrier are briefly discussed.

    Comments:
    12 pages, 8 figures, 1 table. It has been published in Chinese Physics C (2018)
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1803.04616 [pdf]
    CPC(2018)·22 citations
  2. 02

    [Submitted on 13 Mar 2018]

    Coupled-channels analyses for Li + Pb fusion reactions with multi-neutron transfer couplings

    Ki-Seok Choi · Myung-Ki Ceoun · W. Y. So · K. Hagino · K. S. Kim

    We discuss the role of two-neutron transfer processes in the fusion reaction of the Li + Pb systems. We first analyze the Li + Pb reaction by taking into account the coupling to the Li + Pb channel. To this end, we assume that two neutrons are directly transferred to a single effective channel in Pb and solve the coupled-channels equations with the two channels. By adjusting the coupling strength and the effective -value, we successfully reproduce the experimental fusion cross sections for this system. We then analyze the Li + Pb reaction in a similar manner, that is, by taking into account three effective channels with Li + Pb, Li + Pb, and Li + Pb partitions. In order to take into account the halo structure of the Li nucleus, we construct the potential between Li and Pb with a double folding procedure, while we employ a Wood-Saxon type potential with the global Akyüz-Winther parameters for the other channels. Our calculation indicates that the multiple two-neutron transfer process plays a crucial role in the Li + Pb fusion reaction at energies around the Coulomb barrier.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1803.04618 [pdf]
    PLB(2018)·7 citations
  3. 03

    [Submitted on 13 Mar 2018]

    Ground state properties of and nuclei at equilibrium and at large static compression at zero temperature using Nijmegen and Reid Soft Core nucleon-nucleon interactions

    Iyad Alhagaish · Ali Abu-Nada · Feras Afaneh · Mahmoud Hasan

    In this paper, we investigate the ground state properties ( binding energy, nuclear radius, radial density distribution and single particle energies) for and nuclei at equilibrium and at large static compression at zero temperature by using two realistic different potentials namely, Nijmegen and Reid Soft Core (RSC)potentials. We carry out the calculations in No-Core Shell Model space consisting of six major oscillator shells within the framework of the Constrained Spherical Hartree- Fock (CSHF) approximations. We find out that, the computed equilibrium root mean square radii and the Hartree Fock energies for 4He and 12C with those two different potentials are very close to the experimental values of the nuclear radii and nuclear binding energies for the same nuclei.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1803.04650 [pdf]
    1 citation
  4. 04

    [Submitted on 13 Mar 2018]

    Gamow-Teller transitions and neutron-proton-pair transfer reactions

    P. Van Isacker🇫🇷 · A.O. Macchiavelli🇺🇸

    We propose a schematic model of nucleons moving in spin--orbit partner levels, , to explain Gamow--Teller and two-nucleon transfer data in nuclei above Ca. Use of the coupling scheme provides a more transparent approach to interpret the structure and reaction data.We apply the model to the analysis of charge-exchange, Ca(He,t)Sc, and np-transfer, Ca(He,p)Sc, reactions data to define the elementary modes of excitation in terms of both isovector and isoscalar pairs, whose properties can be determined by adjusting the parameters of the model (spin--orbit splitting, isovector pairing strength and quadrupole matrix element) to the available data. The overall agreement with experiment suggests that the approach captures the main physics ingredients and provides the basis for a boson approximation that can be extended to heavier nuclei. Our analysis also reveals that the SU(4)-symmetry limit is not realized in Sc.

    Comments:
    9 pages, 1 figure
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1803.04704 [pdf]
    PLB(2018)·6 citations
  5. 05

    [Submitted on 13 Mar 2018] (cross-list from astro-ph.HE)

    Current status and desired accuracy of the isotopic production cross sections relevant to astrophysics of cosmic rays I. Li, Be, B, C, N

    Yoann Genolini🇧🇪 · David Maurin🇫🇷 · Igor V. Moskalenko🇺🇸 · Michael Unger🇩🇪

    The accuracy of the current generation of cosmic-ray (CR) experiments, such as AMS-02, PAMELA, CALET, and ISS-CREAM, is now reaching 1--3\% in a wide range in energy per nucleon from GeV/n to multi-TeV/n. Their correct interpretation could potentially lead to discoveries of new physics and subtle effects that were unthinkable just a decade ago. However, a major obstacle in doing so is the current uncertainty in the isotopic production cross sections that can be as high as 20--50\% or even larger in some cases. While there is a recently reached consensus in the astrophysics community that new measurements of cross sections are desirable, no attempt to evaluate the importance of particular reaction channels and their required accuracy has been made yet. It is, however, clear that it is a huge work that requires an incremental approach. The goal of this study is to provide the ranking of the isotopic cross sections contributing to the production of the most astrophysically important CR Li, Be, B, C, and N species. In this paper, we (i) rank the reaction channels by their importance for a production of a particular isotope, (ii) provide comparisons plots between the models and data used, and (iii) evaluate a generic beam time necessary to reach a 3\% precision in the production cross-sections pertinent to the AMS-02 experiment. This first roadmap may become a starting point in the planning of new measurement campaigns that could be carried out in several nuclear and/or particle physics facilities around the world. A comprehensive evaluation of other isotopes will be a subject of follow-up studies.

    Comments:
    37 pages, many figures and tables. Comments are welcome
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Experiment (hep-ex); High Energy Physics — Theory (hep-th); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1803.04686 [pdf]
    PRC(2018)·121 citations
  6. 06

    [Submitted on 13 Mar 2018] (cross-list from nucl-ex)

    Effect of direct reaction channels on deep sub-barrier fusion in asymmetric systems

    Md. Moin Shaikh · S. Nath · J. Gehlot · Tathagata Banerjee · Ish Mukul · R.Dubey · A. Shamlath · P. V. Laveen · M. Shareef · A. Jhingan · N. Madhavan · Tapan Rajbongshi and 5 other authors

    A steeper fall of fusion excitation function, compared to the predictions of coupled-channels models, at energies below the lowest barrier between the reaction partners, is termed as deep sub-barrier fusion hindrance. This phenomenon has been observed in many symmetric and nearly-symmetric systems. Different physical origins of the hindrance have been proposed. This work aims to study the probable effects of direct reactions on deep sub-barrier fusion cross sections. Fusion (evaporation residue) cross sections have been measured for the system F+Ta, from above the barrier down to the energies where fusion hindrance is expected to come into play. Coupled-channels calculation with standard Woods-Saxon potential gives a fair description of the fusion excitation function down to energies below the barrier for the present system. This is in contrast with the observation of increasing fusion hindrance in asymmetric reactions induced by increasingly heavier projectiles, \textit{viz.} Li, B, C and O. The asymmetric reactions, which have not shown any signature of fusion hindrance within the measured energy range, are found to be induced by projectiles with lower break-up threshold, compared to the reactions which have shown signatures of fusion hindrance. In addition, most of the -values for light particles pick-up channels are negative for the reactions which have exhibited strong signatures of fusion hindrance, \textit{viz.} C+Pt and O+Pb. Thus, break-up of projectile and particle transfer channels with positive -values seem to compensate for the hindrance in fusion deep below the barrier. Inclusion of break-up and transfer channels within the framework of coupled-channels calculation would be of interest.

    Comments:
    6 Pages 3 figures
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1803.04710 [pdf]
    0 citations
  7. 07

    [Submitted on 13 Mar 2018] (cross-list from hep-ph)

    Dark decay of the neutron

    James M. Cline🇨🇦 · Jonathan M. Cornell🇨🇦

    New decay channels for the neutron into dark matter plus other particles have been suggested for explaining a long-standing discrepancy between the neutron lifetime measured from trapped neutrons versus those decaying in flight. Many such scenarios are already ruled out by their effects on neutron stars, and the decay into dark matter plus photon has been experimentally excluded. Here we explore the decay into a dark Dirac fermion and a dark photon , which can be consistent with all constraints if is a subdominant component of the dark matter. Neutron star constraints are evaded if the dark photon mass to coupling ratio is MeV, depending upon the nuclear equation of state. and the kinetic mixing between U(1) and electromagnetism are tightly constrained by direct and indirect dark matter detection, supernova constraints, and cosmological limits.

    Comments:
    10 pages, 2 figures. v2: Clarifications and references added. Submitted to JHEP. v3: Dark matter self scattering cross section and constraints from direct detection corrected, additional constraints added. v4: Typos corrected. Matches published version
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
    arXiv:
    1803.04961 [pdf]
    JHEP(2018)·80 citations

Affiliations

first authorsco-authorsvia INSPIRE