Nuclear Theory·nucl-th

Thursday·August 13, 2026

13 papers—9 primary·4 cross-listed

01
Nuclear level density studied in odd-mass nuclei in the framework of the projected shell model
Jiaqi Wang · Saumi Dutta · Cui-Juan Lv · Long-Jun Wang · Yang Sun
In a recent article [Phys. Rev. C 108, 034309 (2023)], we proposed a projected shell model method for the calculation of nuclear level density (NLD) in deformed even-even nuclei. The current article presents the subsequent study of NLDs in odd-mass nuclei as well as a comparative analysis between our calculated NLDs in adjacent even-even and odd-A systems. Since one nucleon in the odd-mass system remains blocked from participating in the pair formation, resulting in a weakened pairing (assessed by a smaller BCS pairing gap), pronounced differences between the NLDs in an odd-mass (both even-odd and odd-even) nucleus and its immediate even-even neighbour have been found. In general, the structure-dominated variations, which were found to be prominent in the even-even NLD at low energies, are greatly suppressed in the odd-mass systems. Specifically, from excitation energy as low as 2 MeV, the calculated densities of odd-parity and even-parity levels in odd-mass nuclei show an equal division signaling faster attainment of the statistical behavior. Nuclear level-spin distributions of both parities have been seen to adopt a regular Gaussian shape earlier than that found in the even-even system. Moreover, the pleasant property of our shell-model results, that each of our calculated levels is an eigenstate of angular momentum, allows us to extract the values of the energy-dependent dispersion $σ$ of Ericson's spin-distribution formula and plot $ρ (E, I, π)$ , the energy-, spin-, and parity-dependent level density.
nucl-thPRC(2025)·5 citations
02
Projected shell model description of nuclear level density: Collective, pair-breaking, and multiquasiparticle regimes in even-even nuclei
Jiaqi Wang · Saumi Dutta · Long-Jun Wang · Yang Sun
There is overwhelmingly experimental evidence indicating that excited nuclear states are dominated by quasiparticle (qp) excitations, which form many-body configurations with broken nucleon-pairs from different orbitals. By using these multi-qp states as building blocks for a shell-model basis, we propose a novel shell-model method to calculate the nuclear level density (NLD) in deformed nuclei. The shell-model diagonalization with two-body residual interactions yields a large ensemble of eigenstates of angular momentum and parity. We demonstrate that NLD as a statistical quantity depends sensitively on the structure of deformed single-particle states. As the first example to introduce this method, we take a well-deformed rare-earth nucleus, $^{164}$ Dy, for which NLD has been studied extensively by the Oslo method. By a quantitative comparison with discrete levels from spectroscopic measurements, we show that while the pronounced stepwise structure in the low-energy NLD curve can be understood as the collective excitation and nucleon-pair breaking, the exponential growth of levels in the higher-energy NLD can be described by the combination of the broken-pair states, subject to the Pauli principle. According to the nature of NLD with increasing excitation, we divide the entire NLD curve into (1) collective regime, (2) pair-breaking regime, and (3) multi-qp regime. We discuss the formation mechanism and characteristic features of NLD for the three regimes. In addition, the parity dependence and angular-momentum dependence in NLD are investigated with a strong emphasis on the structure effect.
nucl-thPRC(2023)·12 citations
03
Variational neural-network solution of the two-body $^{17} F$ proton-halo problem with a Coulomb--Whittaker tail
Lucas A. Souza · Tobias Frederico
We present a variational artificial neural-network (VANN) solution of $^{17}$ F in a two-body $^{16}$ O $+ p$ potential model. The calculation uses a standard interaction from the literature as a controlled benchmark for testing whether a neural variational ansatz can reproduce not only bound-state energies and interior wave functions, but also the Coulomb--Whittaker tails that control halo and peripheral-capture observables. The reduced radial wave function is obtained by minimizing the Rayleigh quotient of the radial Schrödinger Hamiltonian with the constraints required by each partial wave. Because the variational energy can converge before the asymptotic normalization is correct, the ansatz combines a neural interior with the charged-particle Coulomb--Whittaker form. In the $s_{1/2}$ channel, the Pauli-forbidden $0 s_{1/2}$ component is computed and the physical one-node branch is checked independently for forbidden-state contamination. The Coulomb--Whittaker-constrained VANN reproduces independent Numerov benchmarks for the compact $d_{5/2}$ ground state and the extended $s_{1/2}$ halo state in energy, nodes, rms radius, and overlap. The compact-state ANC agrees to within one percent, while the halo ANC differs by about $4.2%$ , within the larger numerical sensitivity of the asymptotic extraction. The continuum scattering states are obtained by standard Numerov integration with Coulomb matching; only the bound states are represented by the neural ansatz. Combined with these $p$ -wave scattering states, the VANN bound states yield astrophysical $S$ factors consistent with published benchmarks and data within the accuracy of the adopted two-body model. The results demonstrate the usefulness of physically constrained neural wave functions for tail-sensitive nuclear calculations and identify the asymptotic region as the most sensitive part of the calculation.
nucl-thFew Body Syst.(2026)·0 citations
04
Calculation of tetraneutron-induced reaction cross sections with optical and Hauser-Feshbach statistical models
Hiroyuki Fujioka · Toshihiko Kawano
Interactions of tetraneutrons, which are assumed to be produced in the nuclear fission process, with nuclei are studied in the framework of optical and Hauser-Feshbach statistical models. It predicts a large probability of $^{89} Sr$ production for the tetraneutron-induced reaction on $^{88} Sr$ compared to other isotopes. The same technique is applied to the tetraneutron-induced reaction on $^{27} Al$ and the hexaneutron-induced reaction on natural zinc to revisit two historical multi-neutron experiments performed in the past.
nucl-thEPJA(2026)·0 citations
05
Four-neutron halo model at the unitary limit
R. M Francisco🇧🇷 · D. S. Rosa🇧🇷 · G. Hupin🇫🇷 · T. Frederico🇧🇷 · M. T. Yamashita🇧🇷
In some neutron-rich nuclei usually treated as two-neutron halos, the core can itself be resolved into a subcore-neutron-neutron subsystem, so that four valence neutrons may be involved. To describe this situation, a four-neutron halo model in the unitary limit is developed and applied to $^{22}$ C, $^{19}$ B, and $^{14}$ Be, in which a compact nuclear core is surrounded by two weakly bound spin-singlet neutron pairs occupying different spatial shells, characterized by two independent momentum scales, with the four-neutron wave function fully antisymmetrized. The evolution of the halo structure with the ratio of the two scales is mapped from the limit of well-separated scales, where the system reduces to an effective two-neutron halo around a structured core, to the regime of comparable scales, where the four-neutron character is fully developed. At intermediate ratios, a window is identified in which the dimensionless root-mean-square distances become insensitive to the scale hierarchy and the system behaves approximately as a one-scale configuration. The calculated matter radii of $^{22}$ C and $^{19}$ B are consistent with the most recent experimental values and, within current uncertainties, the matter radius does not discriminate between an effective two-neutron-halo and an explicit four-neutron-halo description of $^{22}$ C. Distinguishing the two pictures requires observables sensitive to the shape of the halo distribution, such as ratios of higher radial moments. For $^{14}$ Be, the computed charge radius is consistent with the value derived from the measured point-proton radius.
nucl-th0 citations
06
Transport properties in binary neutron star mergers: Effect of magnetic field
Pranjal Tambe🇮🇳 · Debarati Chatterjee🇮🇳
In extreme environments such as binary neutron star mergers, temperatures as high as $50$ MeV and magnetic fields up to $1 0^{17}$ G, reach a regime where neutrino transport governs the macroscopic thermodynamic and chemical evolution. Existing merger simulations rely on zero magnetic field neutrino emissivity and opacity, potentially missing critical transport physics in highly magnetized neutron star cores. We present an exact framework for computing charged current Urca emissivity and neutrino opacity at finite temperature and magnetic field. We employ the Nucleon Width Approximation framework to account for the collisional broadening effects dominant in the high-density core. Our calculations demonstrate that extreme magnetic fields significantly enhance charged current neutrino opacity, effectively reducing the mean free path for thermal neutrinos.
nucl-thastro-ph.HEhep-ph0 citations
07
Quasi-real photons as a probe of exotic nuclei
Takashi Nakamura · Carlos A. Bertulani
Coulomb excitation is an inelastic process in which either the target or the projectile is excited by the Coulomb interaction, which can equivalently be described as the absorption of a virtual photon. We discuss Coulomb excitation at relativistic energies, with particular emphasis on Coulomb dissociation, in which an excited projectile subsequently breaks up.
nucl-thhep-ex0 citations
08
Spatial Entanglement Entropy in Nuclear Fission
S.C. Li · J.W. Chen · J.C. Pei
Nuclear fission provides a unique manifestation of spatially nonlocal many-body entanglement. We compute the bipartite spatial entanglement entropy exactly along dynamical fission trajectories, by leveraging the fermionic Gaussian state formulation. Across seven representative fissioning channels, the final entanglement entropy correlates strongly with the intrinsic particle number variance of the fragment, yet exhibits no simple dependence on scission geometries. Most notably the entanglement is significantly suppressed when fragments are magic nuclei, revealing a shell anti-entanglement effect. This work establishes entanglement entropy as a novel lens that extends the conventional conception of nuclear fission.
nucl-th0 citations
09
Impact of perturbative tensor interactions on the spontaneous fission half-lives of superheavy nuclei
R. Rodriguez-Guzman · A. Rakhmankulov · L.M. Robledo · R.N. Bernard
The standard microscopic description of fission, based on the mean-field Hartree-Fock-Bogoliubov approximation and a semi-classical description of tunneling through the fission barrier, has been used to analyse the impact of introducing a (perturbative) tensor term along with the well known Gogny-D1S force in the spontaneous fission half-lives. Calculations in a series of even-even isotopes of superheavy nuclei ranging from nobelium to darmstatium have been carried out. The results show that the tensor term only impacts the height of the first fission barrier and leaves mostly unaffected the pairing properties and therefore the collective inertias. As a consequence of the reduction in the barrier height, the spontaneous fission lifetimes obtained by including the tensor term are significantly smaller than the ones without it bringing the theoretical predictions in closer agreement with experimental data.
nucl-thJ.Phys.G(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE