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Nuclear Theory·nucl-th

Wednesday·May 25, 2016

9 papers—7 primary·2 cross-listed

All9Primary7Cross-lists2
  1. 01

    [Submitted on 24 May 2016]

    Systematics of dynamic moment of inertia in super-deformed bands in Mass ~150 region

    S. Roy

    An empirical semi-classical model have been proposed to investigate the nature of dynamic moment-of-inertia , of the super-deformed (SD) bands in nuclei of mass 150 region. The model incorporates an additional frequency dependent distortion, to the dynamic moment-of-inertia term akin to a vibrational component to explain the extreme spin structure of these bands. Using this model two separate components to the dynamic moment of inertia, have been identified for the SD band structure for the mass 150 region. Three distinct nature of the moment-of-inertia, also have been identified using the two parameter model.

    Comments:
    13 pages, 4 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1605.07295 [pdf]
    0 citations
  2. 02

    [Submitted on 24 May 2016]

    Multipion correlations induced by isospin conservation of coherent emission

    Dhevan Gangadharan🇺🇸

    Recent measurements have revealed a significant suppression of multipion Bose-Einstein correlations in heavy-ion collisions at the LHC. The suppression may be explained by postulating coherent pion emission. Typically, the suppression of Bose-Einstein correlations due to coherence is taken into account with the coherent state formalism in quantum optics. However, since charged pion correlations are most often measured, the additional constraint of isospin conservation, which is absent in quantum optics, needs to be taken into account. As a consequence, correlations emerge between pions of opposite charge. A calculation of the correlations induced by isospin conservation of coherent emission is made for two, three- and four-pion correlation functions and compared to the data from the LHC.

    Comments:
    9 pages, 4 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1605.07296 [pdf]
    PLB(2016)·1 citation
  3. 03

    [Submitted on 24 May 2016]

    Quark confinement potential examined by excitation energy of the Lambda_c and Lambda_b baryons in a quark-diquark model

    Daisuke Jido🇯🇵 · Minori Sakashita🇯🇵

    The possibility to have diquark configuration in heavy baryons, such as Lambda_c and Lambda_b, is examined by a nonrelativistic potential model with a heavy quark and a light scalar diquark. Assuming that the Lambda_c and Lambda_b baryons are composed of the heavy quark and the point-like scalar-isoscalar ud diquark, we solve the two-body Schrodinger equation with the Coulomb plus linear potential and obtain the energy spectra for the heavy baryons. Contrary to our expectation, it is found that the potential determined by the quarkonium spectra fails to reproduce the excitation spectra of the Lambda_c and Lambda_b in the quark-diquark picture, while the Lambda_c and Lambda_b spectra is reproduced with a half strength of the confinement string tension than for the quarkonium. The finite size effect of the diquark is also examined and it is found that introduction of a finite size diquark would resolve the failure of the spectrum reproduction. The Xi_c excitation energy is also calculated and is found to be smaller than Lambda_c in the quark-diquark model. This is not consistent with the experimental observation.

    Comments:
    16 pages, 12 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1605.07339 [pdf]
    PTEP(2016)·17 citations
  4. 04

    [Submitted on 24 May 2016]

    The production of unknown neutron-rich isotopes in U+U collisions at near-barrier energy

    Kai Zhao🇨🇳 · Zhuxia Li🇨🇳 · Yingxun Zhang🇨🇳 · Ning Wang🇨🇳 · Qingfeng Li🇨🇳 · Caiwan Shen🇨🇳 · Yongjia Wang🇨🇳 · Xizhen Wu🇨🇳

    The production cross sections for primary and residual fragments with charge number from =70 to 120 produced in the collision of U+U at 7.0 MeV/nucleon are calculated by the improved quantum molecular dynamics (ImQMD) model incorporated with the statistical evaporation model (HIVAP code). The calculation results predict that about sixty unknown neutron-rich isotopes from element Ra (=88) to Db (=105) can be produced with the production cross sections above the lower bound of mb in this reaction. And almost all of unknown neutron-rich isotopes are emitted at the laboratory angles 60. Two cases, i.e. the production of the unknown uranium isotopes with 244 and that of rutherfordium with 269 are investigated for understanding the production mechanism of unknown neutron-rich isotopes. It is found that for the former case the collision time between two uranium nuclei is shorter and the primary fragments producing the residues have smaller excitation energies of 30 MeV and the outgoing angles of those residues cover a range of 30-60. For the later case, the longer collision time is needed for a large number of nucleons being transferred and thus it results in the higher excitation energies and smaller outgoing angles of primary fragments, and eventually results in a very small production cross section for the residues of Rf with 269 which have a small interval of outgoing angles of =40-50.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1605.07393 [pdf]
    PRC(2016)·61 citations
  5. 05

    [Submitted on 24 May 2016]

    Comment on "Structure effects in the N(n,)N radiative capture reaction from the Coulomb dissociation of N"

    Peter Mohr

    In their recent study Neelam, Shubhchintak, and Chatterjee have claimed that "it would certainly be useful to perform a Coulomb dissociation experiment to find the low energy capture cross section for the reaction" N(n,)N. However, it is obvious that a Coulomb dissociation experiment cannot constrain this capture cross section because the dominating branchings of the capture reaction lead to excited states in N which do not contribute in a Coulomb dissociation experiment. An estimate of the total N(n,)N cross section from Coulomb dissociation of N requires a precise knowledge of the -ray branchings in the capture reaction. Surprisingly, the calculation of Neelam, Shubhchintak, and Chatterjee predicts a strongly energy-dependent ground state branching of the order of 0.05\% to 0.6\% at energies between 100 and 500 keV which is almost 2 orders of magnitude below calculations in the direct capture model. Additionally, this calculation of Neelam, Shubhchintak, and Chatterjee deviates significantly from the expected energy dependence for -wave capture.

    Comments:
    2 pages, 1 figure; Phys. Rev. C, Comment, accepted for publication
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1605.07499 [pdf]
    PRC(2016)·0 citations
  6. 06

    [Submitted on 24 May 2016]

    Nucleosynthesis of Nb and the relevance of the low-lying isomer at 135.5 keV

    Peter Mohr

    Background: Because of its half-life of about 35 million years, 92Nb is considered as a chronometer for nucleosynthesis events prior to the birth of our sun. The abundance of 92Nb in the early solar system can be derived from meteoritic data. It has to be compared to theoretical estimates for the production of 92Nb to determine the time between the last nucleosynthesis event before the formation of the early solar system. Purpose: The influence of a low-lying short-lived isomer on the nucleosynthesis of 92Nb is analyzed. The thermal coupling between the ground state and the isomer via so-called intermediate states affects the production and survival of 92Nb. Method: The properties of the lowest intermediate state in 92Nb are known from experiment. From the lifetime of the intermediate state and from its decay branchings, the transition rate from the ground state to the isomer and the effective half-life of 92Nb are calculated as a function of the temperature. Results: The coupling between the ground state and the isomer is strong. This leads to thermalization of ground state and isomer in the nucleosynthesis of 92Nb in any explosive production scenario and almost 100% survival of 92Nb in its ground state. However, the strong coupling leads to a temperature-dependent effective half-life of 92Nb which makes the 92Nb survival very sensitive to temperatures as low as about 8 keV, thus turning 92Nb at least partly into a thermometer. Conclusions: The low-lying isomer in 92Nb does not affect the production of 92Nb in explosive scenarios. In retrospect this validates all previous studies where the isomer was not taken into account. However, the dramatic reduction of the effective half-life at temperatures below 10 keV may affect the survival of 92Nb after its synthesis in supernovae which are the most likely astrophysical site for the nucleosynthesis of 92Nb.

    Comments:
    5 pages, 3 figures; Phys. Rev. C, accepted for publication
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1605.07502 [pdf]
    PRC(2016)·6 citations
  7. 07

    [Submitted on 17 May 2016]

    Competition between fermions and bosons in nuclear matter at low densities and finite temperatures

    J. Mabiala · H. Zheng · A. Bonasera · Z. Kohley · S.J. Yennello

    We derive the free energy for fermions and bosons from fragmentation data. Inspired by the symmetry and pairing energy of the Weizsacker mass formula we obtain the free energy of fermions (nucleons) and bosons (alphas and deuterons) using Landau's free energy approach. We confirm previously obtained results for fermions and show that the free energy for alpha particles is negative and very close to the free energy for ideal Bose gases. Deuterons behave more similarly to fermions (positive free energy) rather than bosons. This is due to their low binding energy, which makes them very 'fragile', i.e., easily formed and destroyed. We show that the {\alpha}-particle fraction is dominant at all temperatures and densities explored in this work. This is consistent with their negative free energy, which favors clusterization of nuclear matter into {\alpha}-particles at subsaturation densities and finite temperatures. The role of finite open systems and Coulomb repulsion is addressed.

    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1605.07555 [pdf]
    PRC(2016)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE