arXiv subjects

Antonio Bjelčić

Publications and source records attributed to Antonio Bjelčić.

7 recordsLinked to original sources

arXiv2026

Energy-Resolved Spin and Parity Distributions of Fission Fragments

Fission fragments are born rotating rapidly, but the evolution of this spin with excitation energy and its impact on fission observables remain largely unknown. Combining state-of-the-art microscopic and statistical reaction theory, we simulate the full fission process - from the initial state, through scission, to fragment decay - and report the first microscopic, energy-resolved spin and parity distributions of the fragments produced in $^{239}$Pu(n,f). From thermal energy to $E_n = 10$ MeV, the spin of individual fragments evolves non-monotonically, tracking their deformation. The parity content, strongly non-statistical at thermal energy, remains correlated with spin throughout this range. For the first time, we quantify the impact of microscopic spin-parity distributions on prompt photon multiplicities, demonstrating the predictive potential of parameter-free microscopic inputs.

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arXiv2026

Quantum Complexity in Nuclear Scattering and Fission Dynamics

Quantum computers promise advantages for simulating strongly correlated quantum many-body systems, like atomic nuclei, that are beyond the reach of classical computers. Realizing this potential requires understanding the quantum complexity structure of the target problem. We investigate the time-evolution of two key indicators of quantum complexity, bipartite entanglement entropy and non-local magic (non-stabilizerness), in nuclear reaction dynamics. We analyze two representative dynamical processes: scattering in a one-dimensional model of strongly interacting fermions governed by the Negele potential, and a realistic simulation of $^{240}$Pu fission within time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory. In the former case, we find that interactions dynamically generate both entanglement and non-local magic, leaving persistent signatures of quantum complexity in the outgoing states. In the latter, we observe that substantial quantum complexity survives in the spatial bipartition of daughter fragments well beyond scission. The presence of significant non-local magic and entanglement in both cases strongly indicate that quantum computers would provide substantial advantages for accurately simulating nuclear reaction dynamics.

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arXiv2026

Microscopic Spin-Parity Distributions of Fission Fragments

Recent microscopic studies have investigated various features of the spin distributions of fission fragments, but their parity distributions remain largely unexplored. In this Letter, we provide a complete characterization of the spin--parity content of fission fragments within a time-dependent Hartree-Fock-Bogoliubov framework, performing for the first time simultaneous projections on angular momentum, particle number, and parity. Calculations are carried out for the thermal neutron-induced fission of $^{239}$Pu using both the Gogny and Skyrme energy density functionals. We find that dynamical pair breaking during fission populates a significant fraction of unnatural-parity states and generates components with non-zero spin projections $K$. The parity content is found to depend on the number parity of the fragments, with odd-mass nuclei exhibiting pronounced parity staggering and odd-odd nuclei favoring negative parity. These results show that the parity distribution of fragments can depart significantly from the equiprobable partition commonly assumed in statistical de-excitation models, with potential implications for the modeling of fragment decay.

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arXiv2026

Angular and Kinetic Properties of Scission Neutrons within Time-dependent Density Functional Theory

Scission-neutron emission is investigated in $^{235}\mathrm{U}(\mathrm{n}_{\mathrm{th}},\mathrm{f})$, $^{239}\mathrm{Pu}(\mathrm{n}_{\mathrm{th}},\mathrm{f})$ and $^{252}\mathrm{Cf}(\mathrm{sf})$ within time-dependent density functional theory. Using a substantially larger simulation domain than in previous studies, the angular and energy distributions of emitted scission neutrons are extracted over a specific range of emission angles. At these angles, scission neutrons are absent below a threshold energy of roughly $1.5$--$2\,\mathrm{MeV}$, and instead contribute predominantly to the higher energy part of the prompt fission neutron spectrum. Combining the calculated scission-neutron spectrum with a Maxwellian model for the evaporated component, constrained by low-energy experimental data, reproduces the measured high-energy prompt-fission-neutron yield in both $^{239}\mathrm{Pu}(\mathrm{n}_{\mathrm{th}},\mathrm{f})$ and $^{252}\mathrm{Cf}(\mathrm{sf})$, whereas the evaporation-only model systematically underestimates it. This identifies a signature of scission neutrons already present in existing high-energy prompt fission neutron spectra and constitutes direct evidence for a non-negligible scission-neutron component in prompt fission neutron emission.

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arXiv2025

Excitation energy of fission fragments within nuclear time-dependent density functional theory

The number and properties of the neutrons and photons emitted in nuclear fission are directly related to the excitation energy of the fission fragments when they are formed at scission. Though not observable experimentally because of the extremely short time scales, the excitation energy of fission fragments can be predicted by microscopic theory based on time-dependent density functional theory (TDDFT). Initial results on the value of the total kinetic energy of fission reactions were very promising, but could not probe all possible fragmentations. In this work, we perform large-scale TDDFT calculations in $^{240}$Pu enabled by the development of a new TDDFT solver. We obtain TDDFT trajectories covering nearly all possible fragmentations. We find that the total kinetic energy is close to experimental values only for the most likely fission while it is severely underestimated at both small and large asymmetries. This conclusion seems rather independent of the parameterization of the energy functional, both in its particle-hole and particle-particle channels.

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arXiv2024

Computing the QRPA Level Density with the Finite Amplitude Method

We describe a new algorithm to calculate the vibrational nuclear level density of an atomic nucleus. Fictitious perturbation operators that probe the response of the system are generated by drawing their matrix elements from some probability distribution function. We use the Finite Amplitude Method to explicitly compute the response for each such sample. With the help of the Kernel Polynomial Method, we build an estimator of the vibrational level density and provide the upper bound of the relative error in the limit of infinitely many random samples. The new algorithm can give accurate estimates of the vibrational level density. Since it is based on drawing multiple samples of perturbation operators, its computational implementation is naturally parallel and scales like the number of available processing units.

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arXiv2022

Many-body approach to superfluid nuclei in axial geometry

Starting from a general many-body fermionic Hamiltonian, we derive the equations of motion (EOM) for nucleonic propagators in a superfluid system. The resulting EOM is of the Dyson type formulated in the basis of Bogoliubov's quasiparticles. As the leading contributions to the dynamical kernel of this EOM in strongly-coupled regimes contain phonon degrees of freedom in various channels, an efficient method of calculating phonon's characteristics is required to successfully model these kernels. The traditional quasiparticle random phase approximation (QRPA) solvers are typically used for this purpose in nuclear structure calculations, however, they become very prohibitive in non-spherical geometries. In this work, by linking the notion of the quasiparticle-phonon vertex to the variation of the Bogoliubov's Hamiltonian, we show that the recently developed finite-amplitude method (FAM) can be efficiently employed to compute the vertices within the FAM-QRPA. To illustrate the validity of the method, calculations based on the relativistic density-dependent point-coupling Lagrangian are performed for the single-nucleon states in heavy and medium-mass nuclei with axial deformations. The cases of $^{38}$Si and $^{250}$Cf are presented and discussed.

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