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Nuclear Theory·nucl-th

Wednesday·May 22, 2024

5 papers—4 primary·1 cross-listed

All5Primary4Cross-lists1
  1. 01

    [Submitted on 17 May 2024]

    The Kohn-Luttinger Effect in Dense Matter and its Implications for Neutron Stars

    Mia Kumamoto · Sanjay Reddy

    Repulsive short-range interactions can induce p-wave attraction between fermions in dense matter and lead to Cooper pairing at the Fermi surface. We investigate this phenomenon, well-known as the Kohn-Luttinger effect in condensed matter physics, in dense matter with strong short-range repulsive interactions. We find that repulsive interactions required to stabilize massive neutron stars can induce p-wave pairing in neutron and quark matter. When massive vector bosons mediate the interaction between fermions, the induced interaction favors Cooper pairing in the 3P2 channel. For the typical strength of the interaction favored by massive neutron stars, the associated pairing gaps in neutrons can be in the range of 10 keV to 10 MeV. Strong and attractive spin-orbit and tensor forces between neutrons can result in repulsive induced interactions that greatly suppress the 3P2 pairing gap in neutron matter. In quark matter, the induced interaction is too small to result in pairing gaps of phenomenological relevance.

    Comments:
    34 pages, 11 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Superconductivity (cond-mat.supr-con)
    arXiv:
    2405.12243 [pdf]
    PRC(2024)·4 citations
  2. 02

    [Submitted on 21 May 2024]

    Prompt fission neutron spectra of 240Pu(n, F)

    V.M. Maslov

    Variation of fission neutron spectra of 240Pu (sf) and 240Pu (n, F) for E up to 20 MeV predicted.Features of angle-integrated prompt fission neutron spectra of 240Pu (n, F) stem from simultaneous analysis of data for 238U (n, F), 239Pu (n, F) and available data on 240Pu (n, F) prompt fission neutron spectra.The data on average energies of 240Pu (n, F) prompt fission neutron spectra support the approach pursued in case of 238U (n, F) and 239Pu (n, F). Soft influence of exclusive neutron spectra on prompt fission neutron spectra observed in case of 240Pu (n, F) and 240Pu (n, xnf) at E = 7-8 MeV. The largest relative amplitude of exclusive neutron spectra 240Pu (n, xnf) is envisaged at E = 6-6.25 MeV. Prompt fission neutron spectra of 240Pu (n, F) are harder than those of 238U (n,F), but softer than prompt fission neutron spectra for 239Pu(n, F). 240Pu (n, F) prompt fission neutron spectra 240Pu shape is rather close to that of 239Pu(n, F), though the contribution of pre-fission neutrons is relatively higher. Exclusive neutron spectra (n, xnf) are consistent with (n,F) cross sections of 237-240Pu(n, F), as well as neutron emissive spectra of 239Pu(n, xn) at E = 14 MeV. We predict the exclusive pre-fission neutron spectra, exclusive neutron spectra of (n,xn) reactions, average total kinetic energy TKE of fission fragments and products, partials of of average prompt fission neutron number and observed prompt fission neutron spectra.

    Comments:
    5 pages, 6 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2405.12693 [pdf]
    0 citations
  3. 03

    [Submitted on 21 May 2024]

    Small cross section of the synthesis of darmstadtium in the Ca+Th reaction

    A. K. Nasirov · A. Yusupov · B. M. Kayumov

    The smallness of the cross section of evaporation residues formed in the hot fusion reaction Ca+Th is analyzed by the dinuclear system model (DNS). The capture probability has been calculated by solving the dynamical equations of motion for the relative distance between the centers-of-mass of the DNS nuclei. Fusion of nuclei is considered as evolution of the DNS to a stable compound nucleus. The fusion probability has a bell-like shape and quasifission is one of reasons causing smallness of the yield of the evaporation residues products. Another reason is the decrease of the fission barrier for the isotopes Dm related with the shell effects in the neutron structure. The agreement of the theoretical results obtained for the yield of the evaporation residues with the experimental data measured in the Factory of superheavy elements of Joint Institute for Nuclear Research is well.

    Comments:
    9 pages, 9 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2405.12932 [pdf]
    PRC(2024)·6 citations
  4. 04

    [Submitted on 21 May 2024]

    Improved predictions of phenomenological nuclear charge radius formulae with Bayesian optimization approach

    Song-Bo Zhao · Lu Sun · Cai-Xin Yuan · Ying-Chen Mao

    The model inputs play a key role in the performance of the Bayesian optimization approach. In this paper, we investigate the influence of the inputs on the improved predictions of phenomenological nuclear charge radius formulas using an approach combining those original formulas and the Bayesian neural network (BNN). We find that there is no improvement in predictions after the abnormal odd-even staggering effect of 181,183,185Hg is injected into the BNN, while the original phenomenological formulas themselves possess rich physical information or rigid constraints. It indicates the abundance and intensity of physical inputs affect the performance of the Bayesian optimization approach as well as the robustness of the BNN. We further demonstrate that, by ensuring that the number of neurons in the hidden layer is larger than the number of NN inputs, adding hidden layers into the BNN can significantly improve the predictions of nuclear charge radii formulas within the Bayesian optimization approach.

    Comments:
    10 pages,4 figures, 4 talbes
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2405.12936 [pdf]
    1 citation