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Nuclear Theory·nucl-th

Thursday·August 22, 2024

8 papers—3 primary·5 cross-listed

All8Primary3Cross-lists5
  1. 01

    [Submitted on 18 Aug 2024]

    Semiclassical Features of Wobbling and Chiral Properties in Nuclei

    Apolodor Aristotel Raduta · Cristian Mircea Raduta · Robert Poenaru

    A semiclassical approach is used to describe the wobbling and chiral motion in even-even and odd-even nuclei The trial function involved in the variational equation for the quantal action is a coherent state for the SU(2 ) group associated to a triaxial rotor for the case of an even-even system and a coherent state for the group SU(2) SU(2) describing the particle-core system. Application is made for Er and Lu, Pr. Th parameters involved in the coherent state expression are complex numbers depending on time and play the role of the phase space generalized conjugate coordinates whose equation of motion may be brought to the Hamilton canonical form.Within a harmonic approximation one analytically obtains the wobbling frequencies which are further used to calculate the excitation energies for the states forming a band. A new procedure to quantize the classical orbitals is proposed. In the new picture the electromagnetic transition probabilities are calculated both for the in-band and the intraband transitions. Additionally, for odd systems, some other observable like aligned angular momentum, excitation energies relative to a reference spectrum, dynamic moment of energies are calculated and compared with the corresponding experimental data.In the parameter space one identified several nuclear phases with specific properties. An example is given where the wobbling and chiral motions coexist. The existence of a transversal wobbling is widely commented. A new boson representation for the angular momenta is proposed. The approach was successfully applied to Pr. One concludes that semiclassical description is an efficient tool to account quantitatively for the wobbling and chiral properties in nuclei.

    Comments:
    arXiv admin note: text overlap with arXiv:1711.01425
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2408.11073 [pdf]
    0 citations
  2. 02

    [Submitted on 21 Aug 2024]

    Role of momentum in the generator-coordinate method applied to barrier penetration

    K. Hagino · G.F. Bertsch

    Nuclear fission at barrier-top energies is conventionally modeled by a one-dimensional Schrödinger equation applied to internal fission channels, but that treatment is hard to justify in the configuration-interaction approach to nuclear Hamiltonians. Here we show that inclusion of states of finite momentum by the Generator Coordinate Method (GCM) considerably extends the range of energies at which GCM-based Hamiltonians could reproduce the Schrödinger treatment. The transmission probabilities for crossing the barrier are calculated by a discrete version of Kohn's variational method, which may also be useful for other systems of interacting fermions.

    Comments:
    7 pages, 4 figures. To appear in Phys. Rev. C
    Subjects:
    Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph); physics.chem-ph (physics.chem-ph); Quantum Physics (quant-ph)
    arXiv:
    2408.11427 [pdf]
    PRC(2024)·5 citations
  3. 03

    [Submitted on 21 Aug 2024]

    Capture Rates of Highly Degenerate Neutrons

    B. Knight · O. L. Caballero · H. Schatz

    At the low temperature and high density conditions of a neutron star crust neutrons are degenerate. In this work, we study the effect of this degeneracy on the capture rates of neutrons on neutron rich nuclei in accreted crusts. We use a statistical Hauser-Feshbach model to calculate neutron capture rates and find that neutron degeneracy can increase rates significantly. Changes increase from a factor of a few to many orders of magnitude near the neutron drip line. We also quantify uncertainties due to model inputs for masses, -strength functions, and level densities. We find that uncertainties increase dramatically away from stability and that degeneracy tends to increase these uncertainties further, except for cases near the neutron drip line where degeneracy leads to more robustness. As in the case of capture of classically distributed neutrons, variations in the mass model have the strongest impact. Corresponding variations in the reaction rates can be as high as 3 to 4 orders of magnitude, and be more than 5 times larger than under classical conditions. To ease the incorporation of neutron degeneracy in nucleosynthesis networks, we provide tabulated results of capture rates as well as analytical expressions as function of temperature and neutron chemical potential, for proton numbers between , derived from fits to our numerical results. Fits are based on a new parametrization that complements previously employed power law approximations with additional Lorentzian terms that account for low energy resonances, significantly improving accuracy.

    Comments:
    16 pages, 11 figures. Tabulated reaction rates can be found at https://github.com/Nyrb1001/Degenerate-Neutron-Captures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
    arXiv:
    2408.11639 [pdf]
    J.Phys.G(2024)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE