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Nuclear Theory·nucl-th

Thursday·June 9, 2016

4 papers—3 primary·1 cross-listed

All4Primary3Cross-lists1
  1. 01

    [Submitted on 6 Jun 2016]

    Fission waves can oscillate

    Andrew G Osborne · Mark R Deinert

    Under the right conditions, self sustaining fission waves can form in fertile nuclear materials. These waves result from the transport and absorption of neutrons and the resulting production of fissile isotopes. When these fission, additional neutrons are produced and the chain reaction propagates until it is poisoned by the buildup of fission products. It is typically assumed that fission waves are soliton-like and self stabilizing. However, we show that in uranium, coupling of the neutron field to the 239U->239Np->239Pu decay chain can lead to a Hopf bifurcation. The fission reaction then ramps up and down, along with the wave velocity. The critical driver for the instability is a delay, caused by the half-life of 239U, between the time evolution of the neutron field and the production of 239Pu. This allows the 239Pu to accumulate and burn out in a self limiting oscillation that is characteristic of a Hopf bifurcation. Time dependent results are obtained using a numerical implementation of a reduced order reaction-diffusion model for a fast neutron field. Monte Carlo simulations in combination with a linear stability analysis are used to confirm the results for the full system and to establish the parameter space where the Hopf occurs.

    Comments:
    13 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th); nlin.PS (nlin.PS)
    arXiv:
    1606.02557 [pdf]
    0 citations
  2. 02

    [Submitted on 7 Jun 2016]

    Landau theory of nuclear level density and its application in description of nuclear level density in the region of discrete and s-wave neutron resonance energies

    A.Elmas · H.Ahmadov · B.Gonul

    In this work, the reliability of the Landau expression for the nuclear level density calculations is tested, for the first-time, to describe nuclear level densities of some light, intermediate mass and heavy nuclei at excitations corresponding to discrete and s-wave neutron resonance energies. The chi-2 minimizing method is used in treatment of the experimental data for the two suggested energy range of discrete energies given by Nuclear Data Sheet [1] and by the systematic for nuclear level density parametrization in [2]. Our comparison with the related data in the discrete energy range has shown that the results obtained by the Landau expression are better than those of back-shifted Fermi-gas model and constant temperature approximation. This result is also valid for some nuclei of interest when the s-wave neutron resonance level density is included to check theoretical prescriptions in the energy range from initial bound states to unbound states near the neutron binding energy.

    Comments:
    12 pages, 3 tables, 12 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1606.02575 [pdf]
    0 citations
  3. 03

    [Submitted on 8 Jun 2016]

    Rapidity Correlation Structure in Nuclear Collisions

    Sean Gavin🇺🇸 · George Moschelli🇺🇸 · Christopher Zin🇺🇸

    We show that measurements of the rapidity dependence of transverse momentum correlations can be used to determine the characteristic time that dictates the rate of isotropization of the stress energy tensor, as well as the shear viscosity . We formulate methods for computing these correlations using second order dissipative hydrodynamics with noise. Current data are consistent with , but targeted measurements can improve this precision.

    Comments:
    18 pages, 6 figures, version accepted for publication in Phys. Rev. C
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1606.02692 [pdf]
    PRC(2016)·21 citations

Affiliations

first authorsco-authorsvia INSPIRE