Pasta nucleosynthesis: Molecular dynamics simulations of nuclear statistical equilibrium

Caplan, M. E.; Schneider, A.; Horowitz, C. J.; Berry, Don

doi:10.1103/physrevc.91.065802

Cited by 27 publications

(22 citation statements)

References 33 publications

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“…Thus, they cannot be formed in laboratory conditions and the only possible environment in which they can be produced is the ejecta of the mergers of neutron stars [73]. In a similar fashion, the regions of neutron stars with nuclear pasta phases [74][75][76] may be a breading ground for the formation of toroidal nuclei in the ejecta of the merger of neutron stars. The two-proton drip line for toroidal nuclei is characterized by neutron to proton ratio of N/Z ∼ 1.25.…”

Section: Discussionmentioning

confidence: 99%

Extension of the nuclear landscape to hyperheavy nuclei

et al. 2019

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The properties of hyperheavy nuclei and the extension of nuclear landscape to hyperheavy nuclei are extensively studied within covariant density functional theory. Axial reflection symmetric and reflection asymmetric relativistic Hartree-Bogoliubov (RHB) calculations are carried out. The role of triaxiality is studied within triaxial RHB and triaxial relativistic mean field + BCS frameworks. With increasing proton number beyond Z ∼ 130 the transition from ellipsoidal-like nuclear shapes to toroidal ones takes place. The description of latter shapes requires the basis which is typically significantly larger than the one employed for the description of ellipsoidal-like shapes. Many hyperheavy nuclei with toroidal shapes are expected to be unstable towards multifragmentation. However, three islands of stability of spherical hyperheavy nuclei have been predicted for the first time in Ref.[1]. Proton and neutron densities, charge radii, neutron skins and underlying shell structure of the nuclei located in the centers of these islands have been investigated in detail. Large neutron shell gaps at N = 228, 308 and 406 define approximate centers of these islands in neutron number. On the contrary, large proton gap appear only at Z = 154 in the (Z ∼ 156, N ∼ 310) island. As a result, this is the largest island of stability of spherical hyperheavy nuclei found in the calculations. The calculations indicate the stability of the nuclei in these islands with respect of octupole and triaxial distortions. The shape evolution of toroidal shapes along the fission path and the stability of such shapes with respect of fission have been studied. Fission barriers in neutron-rich superheavy nuclei are studied in triaxial RHB framework; the impact of triaxiality on the heights of fission barriers is substantial in some parts of this region. Based on the results obtained in the present work, the extension of nuclear landscape to hyperheavy nuclei is provided.

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Section: Discussionmentioning

confidence: 99%

Extension of the nuclear landscape to hyperheavy nuclei

et al. 2019

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“…In our simulations we consider cubic volumes with periodic boundary conditions and assume that each nucleon interacts solely with the nearest periodic image of other nucleons. All simulations were run on the Big Red 2 supercomputer of Indiana University using the IUMD CPU/GPU hybrid code detailed in References [25,26].…”

Section: Formalismmentioning

confidence: 99%

Effect of topological defects on “nuclear pasta” observables

Schneider¹,

Berry²,

Caplan³

et al. 2016

Phys. Rev. C

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Background The "pasta" phase of nuclear matter may play an important role in the structure and evolution of neutron stars. Recent works suggest nuclear pasta has a high resistivity which could be explained by the presence of long lived topological defects. The defects act as impurities that decrease thermal and electrical conductivity of the pasta.Purpose To quantify how topological defects affect transport properties of nuclear pasta and estimate this effect using an impurity parameter Qimp.Methods Contrast molecular dynamics simulations of up to 409 600 nucleons arranged in parallel nuclear pasta slabs (perfect pasta) with simulations of pasta slabs connected by topological defects (impure pasta). From these simulations compare the viscosity and heat conductivity of perfect and impure pasta to obtain an effective impurity parameter Qimp due to the presence of defects.Results Both the viscosity and thermal conductivity calculated for both perfect and impure pasta are anisotropic, peaking along directions perpendicular to the slabs and reaching a minimum close to zero parallel to them. In our 409 600 nucleon simulation topological defects connecting slabs of pasta reduce both the thermal conductivity and viscosity on average by about 37%. We estimate an effective impurity parameter due to the defects of order Qimp ∼ 30.Conclusions Topological defects in the pasta phase of nuclear matter have an effect similar to impurities in a crystal lattice. The irregularities introduced by the defects reduce the thermal and electrical conductivities and the viscosity of the system. This effect can be parameterized by a large impurity parameter Qimp ∼ 30.

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“…Multifragmentation in nuclear systems has been studied before [28,29], but mostly with nuclear matter (without Coulomb interaction). In a recent work by Caplan et al [30], expanding neutron star matter has been studied as possible explanations for nucleosynthesis in neutron star mergers.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of fragment formation in neutron-rich matter

Alcain

Dorso

2018

Phys. Rev. C

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Background: Neutron stars are astronomical systems with nucleons submitted to extreme conditions. Due to the longer range coulomb repulsion between protons, the system has structural inhomogeneities. Several interactions tailored to reproduce nuclear matter plus screened Coulomb term reproduce these inhomogeneities known as nuclear pasta. These structural inhomogeneities, located in the crust of neutron stars, can also arise in expanding systems depending on the thermodynamic conditions (temperature, proton fraction, . . . ) and the expansion velocity.Purpose: We aim to find the dynamics of the fragments formation for expanding systems simulated according to the little big bang model. This expansion resembles the evolution of neutron stars merger. Method:We study the dynamics of the nucleons with semiclassical molecular dynamics models. Starting with an equilibrium configuration, we expand the system homogeneously until we arrive to an asymptotic configuration (i. e. very low final densities). We study, with four different cluster recognition algorithms, the fragment distribution throughout this expansion and the dynamics of the cluster formation.Results: Studying the topology of the equilibrium states, before the expansion, we reproduced the known pasta phases plus a novel phase we called pregnocchi, consisting of proton aggregates embedded in a neutron sea. We have identified different fragmentation regimes, depending on the initial temperature and fragment velocity. In particular, for the already mentioned pregnocchi, a neutron cloud surrounds the clusters during the early stages of the expansion, resulting in systems that give rise to configurations compatibles with the emergence of r-proccess.Conclusions: These calculations pave the way to a comparision between Earth experiments and neutron star studies.

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Pasta nucleosynthesis: Molecular dynamics simulations of nuclear statistical equilibrium

Cited by 27 publications

References 33 publications

Extension of the nuclear landscape to hyperheavy nuclei

Extension of the nuclear landscape to hyperheavy nuclei

Effect of topological defects on “nuclear pasta” observables

Dynamics of fragment formation in neutron-rich matter

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