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Nuclear Theory·nucl-th

Wednesday·December 9, 2020

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    Study of angular momentum effects in fission

    R. Vogt (LLNL and UC Davis) · J. Randrup (LBNL)

    Background: The role of angular momentum in fission has long been discussed but the observable effects are difficult to quantify. Purpose: We discuss a variety of effects associated with angular momentum in fission and present quantitative illustrations. Methods: We employ the fission simulation model which is well suited for this purpose because it obeys all conservation laws, including linear and angular momentum conservation at each step of the process. We first discuss the implementation of angular momentum in and then assess particular observables, including various correlated observables. We also study potential effects of neutron-induced fission of the low-lying isomeric state of U relative to the ground state. Results: The fluctuations inherent in the fission process ensure that the spin of the initial compound nucleus has only a small influence on the fragment spins which are therefore nearly uncorrelated. There is a marked correlation between the spin magnitude of the fission fragments and the photon multiplicity. We also consider the dynamical anisotropy caused by the rotation of an evaporating fragment and study especially the distribution of the projected neutron-neutron opening angles, showing that while it is dominated by the effect of the evaporation recoils, it is possible to extract the signal of the dynamical anisotropy by means of a Fourier decomposition. Finally, we note that the use of an isomeric target, U(,f), may enhance the symmetric yields and can thus result in higher neutron multiplicities for low total fragment kinetic energy.

    nucl-thPRC(2021)·46 citations
  2. 02

    Electric dipole response of low-lying excitations in the two-neutron halo nucleus F

    J. Casal · Jagjit Singh · L. Fortunato · W. Horiuchi · A. Vitturi

    The neutron-rich F isotopes have been recently studied via knockout and interaction cross-section measurements. The halo in F has been linked to the occupancy of intruder configurations. We investigate bound and continuum states in F, focusing on the response of low-lying excitations and the effect of dipole couplings on nuclear reactions. () wave functions are built within the hyperspherical harmonics formalism, and reaction cross sections are calculated using the Glauber theory. Continuum states and transition probabilities are described in a pseudostate approach using the analytical THO basis. The corresponding structure form factors are used in CDCC calculations to describe low-energy scattering. Parity inversion in F leads to a F ground state characterized by 57.5% of intruder components, a strong dineutron configuration, and an increase of the matter radius with respect to the core radius of fm. Glauber-model calculations for a carbon target at 240 MeV/nucleon provide a total reaction cross section of 1370 mb, in agreement with recent data. The model produces also a barely bound excited state corresponding to a quadrupole excitation. calculations into the continuum yield a total strength of 1.59 efm up to 6 MeV, and the distribution exhibits a resonance at 0.85 MeV. Results using a standard shell-model order for F lead to a considerable reduction of the distribution. The four-body CDCC calculations for around the Coulomb barrier are dominated by dipole couplings, which totally cancel the Fresnel peak in the elastic cross section. These results are consistent with a two-neutron halo and may guide future experimental campaigns.

    nucl-thnucl-exPRC(2020)·33 citations
  3. 03

    The Shape of the Correlation Function

    Jakub Cimerman🇨🇿 · Chrisopher Plumberg🇸🇪 · Boris Tomášik🇨🇿

    The correlation function measured in ultrarelativistic nuclear collisions is strongly non-Gaussian. Using two different models we study which effects can influence its shape and how much. In particular, we focus on the parametrizations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as resonance decays, event-by-event fluctuations and functional dependence on or similar. We also study the corrections including the first-order Lévy expansion.

    nucl-thhep-phnucl-exPoS(2021)·2 citations
  4. 04

    Forward quark jet-nucleus scattering in a light-front Hamiltonian approach

    Meijian Li🇫🇮

    We investigate the scattering of a quark jet on a high-energy heavy nucleus using the time-dependent light-front Hamiltonian approach. We simulate a real-time evolution of the quark in a strong classical color field of the relativistic nucleus, described as the Color Glass Condensate. We study the sub-eikonal effect by letting the quark jet carry realistic finite longitudinal momenta, and we find sizeable changes on the transverse coordinate distribution of the quark. We also observe the energy loss of the quark through gluon emissions in the Fock space. This approach provides us with an opportunity to study scattering processes from non-perturbative aspects.

    nucl-thhep-phPoS(2021)·1 citation
  5. 05

    Nuclear deformation as a source of the non-linearity of King plot in the Yb ion

    Saleh O. Allehabi · V. A. Dzuba · V. V. Flambaum · A. V. Afanasjev

    We perform atomic relativistic many-body calculations of the field isotope shifts and calculations of corresponding nuclear parameters for all stable even-even isotopes of Yb ion. We demonstrate that if we take nuclear parameters of the Yb isotopes from a range of the state-the-art nuclear models which all predict strong quadrupole nuclear deformation, then calculated non-linearity of the King plot, caused by the difference in the deformation in different isotopes, is consistent with the non-linearity observed in the experiment (Ian Counts {\em et al}, Phys. Rev. Lett. {\bf 125}, 123002 (2020)). The changes of nuclear RMS radius between isotopes extracted from experiment are consistent with those obtained in the nuclear calculations.

    ↳ physics.atom-phnucl-thPRA(2021)·36 citations
  6. 06

    On nuclear coalescence in small interacting systems

    M. Kachelriess🇳🇴 · S. Ostapchenko🇷🇺 · J. Tjemsland🇳🇴

    The formation of light nuclei can be described as the coalescence of clusters of nucleons into nuclei. In the case of small interacting systems, such as dark matter and annihilations or collisions, the coalescence condition is often imposed only in momentum space and hence the size of the interaction region is neglected. On the other hand, in most coalescence models used for heavy ion collisions, the coalescence probability is controlled mainly by the size of the interaction region, while two-nucleon momentum correlations are either neglected or treated as collective flow. Recent experimental data from collisions at LHC have been interpreted as evidence for such collective behaviour, even in small interacting systems. We argue that these data are naturally explained in the framework of conventional QCD inspired event generators when both two-nucleon momentum correlations and the size of the hadronic emission volume are taken into account. To include both effects, we employ a per-event coalescence model based on the Wigner function representation of the produced nuclei states. This model reproduces well the source size for baryon emission and the coalescence factor measured recently by the ALICE collaboration in collisions.

    ↳ hep-phnucl-thEPJA(2021)·32 citations

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first authorsco-authorsvia INSPIRE