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Nuclear Theory·nucl-th

Wednesday·October 28, 2020

11 papers—7 primary·4 cross-listed

All11Primary7Cross-lists4
  1. 01

    [Submitted on 26 Oct 2020]

    Extension of the Hauser-Feshbach Fission Fragment Decay Model to Multi-Chance Fission

    A.E. Lovell · T. Kawano · S. Okumura · I. Stetcu · M.R. Mumpower · P. Talou

    The Hauser-Feshbach fission fragment decay model, , which calculates the statistical decay of fission fragments, has been expanded to include multi-chance fission, up to neutron incident energies of 20 MeV. The deterministic decay takes as input pre-scission quantities - fission probabilities and the average energy causing fission - and post-scission quantities - yields in mass, charge, total kinetic energy, spin, and parity. From these fission fragment initial conditions, the full decay is followed through both prompt and delayed particle emissions, allowing for the calculation of prompt neutron and properties, such as multiplicity and energy distributions, both independent and cumulative fission yields, and delayed neutron observables. In this work, we describe the implementation of multi-chance fission into the model, and show an example of prompt and delayed quantities beyond first-chance fission, using the example of neutron-induced fission on U. This expansion represents significant progress in consistently modeling the emission of prompt and delayed particles from fissile systems.

    Comments:
    15 pages, 11 figures, submitted to PRC
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2010.13919 [pdf]
    PRC(2021)·40 citations
  2. 02

    [Submitted on 24 Oct 2020]

    Scattering matrix pole expansions for complex wavenumbers in -matrix theory

    Pablo Ducru · Vladimir Sobes · Gerald Hale · Mark Paris · Benoit Forget

    In this follow-up article to [Shadow poles in the alternative parametrization of R-matrix theory, Ducru (2020)], we establish new results on scattering matrix pole expansions for complex wavenumbers in R-matrix theory. In the past, two branches of theoretical formalisms emerged to describe the scattering matrix in nuclear physics: R-matrix theory, and pole expansions. The two have been quite isolated from one another. Recently, our study of Brune's alternative parametrization of R-matrix theory has shown the need to extend the scattering matrix (and the underlying R-matrix operators) to complex wavenumbers. Two competing ways of doing so have emerged from a historical ambiguity in the definitions of the shift and penetration functions: the legacy Lane \& Thomas "force closure" approach, versus analytic continuation (which is the standard in mathematical physics). The R-matrix community has not yet come to a consensus as to which to adopt for evaluations in standard nuclear data libraries, such as ENDF. In this article, we argue in favor of analytic continuation of R-matrix operators. We bridge R-matrix theory with the Humblet-Rosenfeld pole expansions, and unveil new properties of the Siegert-Humblet radioactive poles and widths, including their invariance properties to changes in channel radii . We then show that analytic continuation of R-matrix operators preserves important physical and mathematical properties of the scattering matrix -- cancelling spurious poles and guaranteeing generalized unitarity -- while still being able to close channels below thresholds.

    Comments:
    Under review in Phys. Rev. C. 23 pages, 1 figure, 1 table. arXiv admin note: substantial text overlap with arXiv:1903.02661
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2010.14062 [pdf]
    PRC(2021)·3 citations
  3. 03

    [Submitted on 27 Oct 2020]

    Final state interaction in the pn and nn decay channels of He

    C.A. Bertulani · R. Lobato

    We study the effects of final state interactions in the non-mesonic weak decay (n is a neutron and N is either a neutron or a proton) of the hypernucleus He. Using a three-body model the effects of distortion of the interaction of the emitted nucleon pair with the residual nucleus is considered. We also study the influence of the final state interaction between the emitted nucleons using the Migdal-Watson model. The effect of spin symmetries in the final state of the pair is also considered. Based on our calculations, we conclude that final state interactions play a minor role in the kinetic energy spectrum of the emitted nucleon pair.

    Comments:
    10 pages, 4 figures, version to appear in Eur. J. Phys. A
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2010.14083 [pdf]
    EPJA(2021)·1 citation
  4. 04

    [Submitted on 27 Oct 2020]

    Symmetry-projected variational calculations with the numerical suite TAURUS I. Variation after particle-number projection

    Benjamin Bally🇪🇸 · Adrián Sánchez-Fernández🇪🇸 · Tomás R. Rodríguez🇪🇸

    We present the numerical code TAURUS_vap that solves the variation after particle-number projection equations for symmetry-unrestricted real Bogoliubov quasiparticle states represented in a spherical harmonic oscillator basis. The model space considered is invariant under spatial and isospin rotations but no specific set of orbits is assumed such that the code can carry out both valence-space and no-core calculations. In addition, no number parity is assumed for the Bogoliubov quasiparticle states such that the code can be used to describe even-even, odd-even and odd-odd nuclei. The variational procedure can be performed under several simultaneous constraints on the expectation values of a variety of operators such as the multipole deformations, the pairing field or the components of the angular momentum. To demonstrate the potential and versatility of the code, we perform several example calculations using an empirical shell-model interaction as well as a chiral interaction. The ability to perform advanced variational Bogoliubov calculations offered by this code will, we hope, be beneficial to the shell model and ab initio communities.

    Comments:
    22 pages, 3 figures Accepted version (with some typo corrections)
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2010.14169 [pdf]
    EPJA(2021)·29 citations
  5. 05

    [Submitted on 24 Oct 2020]

    Roton instabilities in the superfluid outer core of neutron stars

    J. A. Gil Granados · A. Muñoz Mateo · X. Viñas

    We study the superfluid dynamics of the outer core of neutron stars by means of a hydrodynamic model made of a neutronic superfluid and a protonic superconductor, coupled by both the dynamic entrainment and the Skyrme SLy4 nucleon-nucleon interactions. The resulting nonlinear equations of motion are probed in the search for dynamical instabilities triggered by the relative motion of the superfluids that could be related to observed timing anomalies in pulsars. Through linear analysis, the origin and expected growth of the instabilities is explored for varying nuclear-matter density. Differently from previous findings, the dispersion of linear excitations in our model shows rotonic structures below the pair-breaking energy threshold, which lies at the origin of the dynamical instabilities, and could eventually lead to emergent vorticity along with modulations of the superfluid density.

    Comments:
    10 pages, 5 figures. v2: minor changes
    Subjects:
    Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas)
    arXiv:
    2010.14222 [pdf]
    PRC(2021)·1 citation
  6. 06

    [Submitted on 27 Oct 2020]

    Constraining the density dependence of the symmetry energy: the isospin transport ratio revisited

    S. Mallik · F. Gulminelli

    The isospin diffusion of the quasi-projectile formed in the on reactions in the Fermi energy domain is investigated in the framework of the Boltzmann-Uehling-Uhlenbeck transport model. The well known isospin transport ratio observable is revisited, with the aim of insuring an optimal comparison between experimental data and theoretical calculations and reducing the present uncertainties in the extraction of empirical equation of state parameters. We show that isospin transport ratios are sensitive to all the low order isovector parameters (, and ). We demonstrate that realistic models of the equation of state, covering the uncertainty that presently affects the theoretical description of neutron stars static observables, can be effectively discriminated by isospin diffusion experiments, provided the neutron to proton ratio of the projectile remnant is precisely measured as a function of centrality.

    Comments:
    5 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2010.14369 [pdf]
    J.Phys.G(2022)·9 citations
  7. 07

    [Submitted on 27 Oct 2020]

    Investigation of low-lying resonances in breakup of halo nuclei within the time-dependent approach

    D.S. Valiolda · D.M. Janseitov · V.S. Melezhik

    We investigate the Coulomb breakup of Be halo nuclei on a heavy target from intermediate (70 MeV/nucleon) to low energies (5 MeV/nucleon) within the non-perturbative time-dependent approach. The convergence of the computational scheme is demonstrated in this energy range including \textit{n}+Be low-lying resonances in different partial and spin states. We have found a considerable contribution of the resonance (= 1.23 MeV) to the breakup cross section at 30 MeV/nucleon and lower, while at higher energies, the resonant states and (with = 2.78 and 3.3 MeV) make most visible contributions. The obtained results are in good agreement with experimental data available at 69 and 72 MeV/nucleon. Comparison with the existing theoretical calculations of other authors for 20 and 30 MeV/nucleon is also made. The developed computational scheme opens new possibilities in the investigation of the Coulomb, as well as nuclear, breakup of other halo nuclei on heavy and light targets.

    Comments:
    23 pages, 12 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2010.14435 [pdf]
    EPJA(2022)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE