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Nuclear Theory·nucl-th

Wednesday·July 2, 2025

15 papers—5 primary·10 cross-listed

All15Primary5Cross-lists10
  1. 01

    Shell effects in quasi-fission for calcium induced reactions forming thorium isotopes

    C. Simenel · A.S. Umar · K. Godbey · P. McGlynn

    Quantum shell effects induce an asymmetric fission mode in actinides, which disappears in neutron deficient isotopes. Quasi-fission, characterized by a significant mass transfer in heavy ion collisions at low-energies, is expected to be affected by similar shell effects. This is studied in 40-56Ca+176Yb reactions with the time-dependent Hartree-Fock approach. All reactions exhibit a mass equilibration process that stops when a heavy fragment with Z~54 protons is formed. Unlike the fission of thorium compound nuclei, quasi-fission does not exhibit a transition to symmetric modes in neutron deficient systems. This observation is interpreted in terms of potential energy surfaces that show a persistence of an asymmetric valley with an increasing barrier preventing its population in fission of the most neutron deficient thorium isotopes.

    nucl-thPLB(2025)·4 citations
  2. 02

    Optimized binning for response function reconstruction via Chebyshev expansions

    Immo C. Reis · Joanna E. Sobczyk · Sonia Bacca

    We propose an optimized histogram binning strategy to reconstruct nuclear response functions via the Chebyshev expansion bound-state method. Our approach employs a stochastic regularization of the density of states to define adaptive, equal-area bins. Using the deuteron solved in a harmonic-oscillator basis with a chiral interaction, we benchmark on dipole and longitudinal responses, obtaining excellent agreement with exact theory and experiment. This general framework readily extends to other many-body systems and opens the door to new ab initio calculations of lepton-nucleus cross sections in medium-mass nuclei.

    nucl-thPRC(2025)·1 citation
  3. 03

    Microscopic pairing in fission dynamics

    A. Zdeb · A. Baran · S.A. Giuliani · L.M. Robledo · M. Warda

    Nuclear fission can be modelled as a quantum tunneling process driven by the interplay between the nuclear binding energy and the collective inertia. Within the Wentzel-Kramers-Brillouin formalism, spontaneous fission half-lives can be obtained by minimizing the action integral in the multidimensional space of collective degrees of freedom. Hence, including the relevant collective variables is crucial for properly describing spontaneous fission probabilities. Pairing correlations play an essential role in this evaluation since the collective inertia decreases as the inverse of the square of the pairing gap, and, therefore, they should be considered as a relevant degree of freedom on the same footing as deformation parameters. In this work, we show that the spontaneous fission half-lives in fermium isotopes can be reproduced in a microscopic theory by considering the least-action fission path in a two-dimensional space with constraints on the quadrupole moment and pairing correlations. We consider two microscopic quantities as degrees of freedom associated with pairing: the pairing gap parameter , and the particle number fluctuations . Least-action paths, computed using the Dijkstra algorithm, are compared with minimum-energy paths, highlighting the importance of pairing correlations as a dynamical degree of freedom.

    nucl-thPRC(2025)·2 citations
  4. 04

    Collectivity of rotational motion in Rn and Ra

    Artur Dobrowolski · Katarzyna Mazurek · Krzysztof Pomorski

    Calculations to reconstruct rotational level patterns in the Rn and Ra nuclei have been performed using a collective quadrupole+octupole approach with microscopic mass tensor and moments of inertia dependent on deformation and pairing degrees of freedom. The main objective is to quantitatively confirm the known experimental observations that the Rn nucleus passes from octupole vibrational to octupole deformed with increasing rotation frequency, while the Ra nucleus is relatively weakly affected by collective rotation, being octupole deformed from the beginning. The collective potential in a nine-dimensional collective space is determined using the macroscopic-microscopic method with Strutinsky and the BCS with an approximate particle number projection microscopic corrections. The corresponding Hamiltonian is diagonalized based on the projected solutions of the harmonic oscillators coupled with Wigner functions. Such an orthogonalized basis is additionally symmetrized with respect to the so-called intrinsic symmetrization group, specifically dedicated to the collective space used, to ensure the uniqueness of the Hamiltonian eigen-solutions in the laboratory frame. The response of the pairing and deformation degrees of freedom to external rotation is discussed in the variational approach, where the total energy is minimized by the deformation and pairing variables. Consequently, the corresponding microscopic moments of inertia increase with collective spin (Coriolis {\it antiparing} effect), resulting in effectively lower rotational energy levels I with respect to pure classical-rotor pattern I(I+1). The obtained comparison of experimental and theoretical rotational energy level schemes, dipole, quadrupole and octupole transition probabilities of B(E) in Rn and Ra is satisfactory.

    nucl-thnucl-exPRC(2025)·1 citation
  5. 05

    New angular momentum coupling method based on Wigner rotation theory

    Junchao Guo · Yang Sun

    We present a new method for constructing the total angular momentum of many-nucleon states. We find that the restrictions imposed by the fermion antisymmetry on the total state are fully absorbed into the single-j space when the broken rotational symmetry of the product state is restored by angular momentum projection. For different j-shells, any total angular momentum that obeys the selection rule is allowed, just as for non-identical particles. The method based on this reorganization is conceptually different from the traditional J and m schemes and may help to improve the efficiency of angular momentum coupling in nuclear many-body calculations.

    nucl-thPRC(2025)·1 citation

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