المؤلفون: Li, B., Vretenar, D., Nikšić, T., Zhao, P. W., Meng, J.

مصطلحات موضوعية: Nuclear Theory

الوصف: A microscopic finite-temperature model based on time-dependent nuclear density functional theory (TDDFT), is employed to study the induced-fission process of $^{226}$Th. The saddle-to-scission dynamics of this process is explored, starting from various points on the deformation surface of Helmholtz free energy at a temperature that corresponds to the experimental excitation energy, and following self-consistent isentropic fission trajectories as they evolve toward scission. Dissipation effects and the formation of excited fragments are investigated and, in particular, the difference in the evolution of the local temperature along asymmetric and symmetric fission trajectories. The relative entropies and entanglement between fission fragments emerging at scission are analyzed.
Comment: 23 pages, 5 figures. arXiv admin note: text overlap with arXiv:2209.02419

الوصول الحر: http://arxiv.org/abs/2406.11124Test

المؤلفون: Li, B., Vretenar, D., Nikšić, T., Zhang, D. D., Zhao, P. W., Meng, J.

مصطلحات موضوعية: Nuclear Theory

الوصف: Nuclear reactions present an interesting case for studies of the time-evolution of entanglement between complex quantum systems. In this work, the time-dependent nuclear density functional theory is employed to explore entanglement in multinucleon transfer reactions. As an illustrative example, for the reaction $^{40}$Ca $+$ $^{208}$Pb at $E_{\rm lab} = 249$ MeV, in the interval of impact parameters $4.65-7.40$ fm, and the relativistic density functional PC-PK1, we compute the von Neumann entropies, entanglement between fragments, nucleon-number fluctuations, and Shannon entropy for the nucleon-number observable. A simple linear correlation is established between the entanglement and nucleon-number fluctuation of the final fragments. The entanglement between the fragments can be related to the corresponding excitation energies and angular momenta. The relationship between the von Neumann entropy and the Shannon entropy for the nucleon-number observable is analyzed, as well as the time-evolution of the entanglement (nucleon-number fluctuation). The entanglement is also calculated for a range of incident energies and it is shown how, depending on the impact parameter, the entanglement increases with the collision energy.
Comment: 22 pages, 7 figures

الوصول الحر: http://arxiv.org/abs/2403.19288Test

المؤلفون: Zhang, D. D., Vretenar, D., NikšIć, T., Zhao, P. W., Meng, J.

المصدر: Phys. Rev. C 109, 024614 (2024)

مصطلحات موضوعية: Nuclear Theory

الوصف: The microscopic framework of time-dependent covariant density functional theory is applied to study multinucleon transfer reactions, with transfer probabilities calculated using the particle number projection method. It is found that similar total cross sections are obtained with two different relativistic density functionals, PC-PK1 and DD-ME2, as well as with the Skyrme functional SLy5 in a previous study, for multinucleon transfer in the reactions: $^{40}{\rm Ca}+{}^{124}{\rm Sn}$ at $E_{\rm lab} = 170$ MeV, $^{40}{\rm Ca}+{}^{208}{\rm Pb}$ at $E_{\rm lab} = 249$ MeV, and $^{58}{\rm Ni}+{}^{208}{\rm Pb}$ at $E_{\rm lab} = 328.4$ MeV. We report the first microscopic calculation of total cross sections for the reactions: $^{40}{\rm Ar}+{}^{208}{\rm Pb}$ at $E_{\rm lab} = 256$ MeV and $^{206}{\rm Pb}+{}^{118}{\rm Sn}$ at $E_{\rm lab} = 1200$ MeV. Compared to the results obtained with the GRAZING model, the cross sections predicted by the time-dependent covariant density functional theory are in much better agreement with data, and demonstrate the potential of microscopic models based on relativistic density functionals for the description of reaction dynamics.
Comment: 20 pages, 5 figures

الوصول الحر: http://arxiv.org/abs/2401.06539Test

المؤلفون: Xiang, J., Li, Z. P., Nikšić, T., Vretenar, D., Long, W. H., Wu, X. Y.

مصطلحات موضوعية: Nuclear Theory

الوصف: The triaxial quadrupole collective Hamiltonian, based on relativistic energy density functionals, is extended to include a pairing collective coordinate. In addition to triaxial shape vibrations and rotations, the model describes pairing vibrations and the coupling between triaxial shape and pairing degrees of freedom. The parameters of the collective Hamiltonian are determined by a covariant energy density functional, with constraints on the intrinsic triaxial shape and pairing deformations. The effect of coupling between triaxial shape and pairing degrees of freedom is analyzed in a study of low-lying spectra and transition rates of $^{128}$Xe. When compared to results obtained with the standard triaxial quadrupole collective Hamiltonian, the inclusion of dynamical pairing compresses the low-lying spectra and improves interband transitions, in better agreement with data. The effect of zero-point energy (ZPE) correction on low-lying excited spectra is also discussed.
Comment: 11 pages, 8 figures, Submitted to Phys. Rev. C. arXiv admin note: text overlap with arXiv:2002.00327

الوصول الحر: http://arxiv.org/abs/2312.01791Test

المؤلفون: Zhang, D. D., Li, B., Vretenar, D., Nikšić, T., Ren, Z. X., Zhao, P. W., Meng, J.

المصدر: Phys. Rev. C 109, 024316 (2024)

مصطلحات موضوعية: Nuclear Theory

الوصف: The microscopic framework of time-dependent covariant density functional theory is applied to a systematic study of ternary quasifission in collisions of pairs of $^{238}$U nuclei. It is shown that the inclusion of octupole degree of freedom in the case of head-to-head collisions, extends the energy window in which ternary quasifission occurs, and greatly enhances the number of nucleons contained in a middle fragment. Dynamical pairing correlations, included here in the time-dependent BCS approximation, prevent the occurrence of ternary quasifission in head-to-head collisions, and have an effect on the location of the energy window in which a middle fragment is formed in tail-to-tail collisions. In the latter case, as well as for tail-to-side collisions, the formation of very heavy neutron-rich systems in certain energy intervals is predicted.
Comment: 23 pages, 13 figures

الوصول الحر: http://arxiv.org/abs/2310.02657Test

المؤلفون: Li, B., Vretenar, D., Nikšić, T., Zhao, J., Zhao, P. W., Meng, J.

المصدر: Front. Phys. 19, 44201 (2024)

مصطلحات موضوعية: Nuclear Theory

الوصف: The generalized time-dependent generator coordinate method (TD-GCM) is extended to include pairing correlations. The correlated GCM nuclear wave function is expressed in terms of time-dependent generator states and weight functions. The particle-hole channel of the effective interaction is determined by a Hamiltonian derived from an energy density functional, while pairing is treated dynamically in the standard BCS approximation with time-dependent pairing tensor and single-particle occupation probabilities. With the inclusion of pairing correlations, various time-dependent phenomena in open-shell nuclei can be described more realistically. The model is applied to the description of saddle-to-scission dynamics of induced fission. The generalized TDGCM charge yields and total kinetic energy distribution for the fission of 240Pu, are compared to those obtained using the standard time-dependent density functional theory (TD-DFT) approach, and with available data.
Comment: 25 pages,9 figures. arXiv admin note: text overlap with arXiv:2304.13369

الوصول الحر: http://arxiv.org/abs/2309.12564Test

المؤلفون: Li, B., Vretenar, D., Nikšić, T., Zhao, P. W., Meng, J.

مصطلحات موضوعية: Nuclear Theory

الوصف: An implementation of the generalized time-dependent generator coordinated method (TD-GCM) is developed, that can be applied to the dynamics of small- and large-amplitude collective motion of atomic nuclei. Both the generator states and weight functions of the GCM correlated wave function depend on time. The initial generator states are obtained as solutions of deformation-constrained self-consistent mean-field equations, and are evolved in time by the standard mean-field equations of nuclear density functional theory (TD-DFT). The TD-DFT trajectories are used as a generally non-orthogonal and overcomplete basis in which the TD-GCM wave function is expanded. The weights, expressed in terms of a collective wave function, obey a TD-GCM (integral) equation. In this explorative paper, the generalized TD-GCM is applied to the excitation energies and spreading width of giant resonances, and to the dynamics of induced fission. The necessity of including pairing correlations in the basis of TD-DFT trajectories is demonstrated in the latter example.
Comment: 30 pages,11 figures

الوصول الحر: http://arxiv.org/abs/2304.13369Test

المؤلفون: Zhao, J., Ebran, J. -P., Heitz, L., Khan, E., Mercier, F., Niksic, T., Vretenar, D.

مصطلحات موضوعية: Nuclear Theory

الوصف: Alpha and cluster decays are analyzed for heavy nuclei located above $^{208}$Pb on the chart of nuclides: $^{216-220}$Rn and $^{220-224}$Ra, that are also candidates for observing the $2 \alpha$ decay mode. A microscopic theoretical approach based on relativistic Energy Density Functionals (EDF), is used to compute axially-symmetric deformation energy surfaces as functions of quadrupole, octupole and hexadecupole collective coordinates. Dynamical least-action paths for specific decay modes are calculated on the corresponding potential energy surfaces. The effective collective inertia is determined using the perturbative cranking approximation, and zero-point and rotational energy corrections are included in the model. The predicted half-lives for $\alpha$-decay are within one order of magnitude of the experimental values. In the case of single $\alpha$ emission, the nuclei considered in the present study exhibit least-action paths that differ significantly up to the scission point. The differences in alpha-decay lifetimes are not only driven by Q values, but also by variances of the least-action paths prior to scission. In contrast, the $2 \alpha$ decay mode presents very similar paths from equilibrium to scission, and the differences in lifetimes are mainly driven by the corresponding Q values. The predicted $^{14}$C cluster decay half-lives are within three orders of magnitudes of the empirical values, and point to a much more complex pattern compared to the alpha-decay mode.
Comment: 9 pages, 13 figures

الوصول الحر: http://arxiv.org/abs/2211.14135Test

المؤلفون: Li, B., Vretenar, D., Ren, Z. X., Nikšić, T., Zhao, J., Zhao, P. W., Meng, J.

مصطلحات موضوعية: Nuclear Theory

الوصف: The saddle-to-scission dynamics of the induced fission process is explored using a microscopic finite-temperature model based on time-dependent nuclear density functional theory (TDDFT), that allows to follow the evolution of local temperature along fission trajectories. Starting from a temperature that corresponds to the experimental excitation energy of the compound system, the model propagates the nucleons along isentropic paths toward scission. For the four illustrative cases of induced fission of $^{240}$Pu, $^{234}$U, $^{244}$Cm, and $^{250}$Cf, characteristic fission trajectories are considered, and the partition of the total energy into various kinetic and potential energy contributions at scission is analyzed, with special emphasis on the energy dissipated along the fission path and the prescission kinetic energy. The model is also applied to the dynamics of neck formation and rupture, characterized by the formation of few-nucleon clusters in the low-density region between the nascent fragments.
Comment: 31 pages, 10 figures

الوصول الحر: http://arxiv.org/abs/2209.02419Test

المؤلفون: Li, Z. P., Vretenar, D.

مصطلحات موضوعية: Nuclear Theory

الوصف: Collective motion is a manifestation of emergent phenomena in medium-heavy and heavy nuclei. A relatively large number of constituent nucleons contribute coherently to nuclear excitations (vibrations, rotations) that are characterized by large electromagnetic moments and transition rates. Basic features of collective excitations are reviewed, and a simple model introduced that describes large-amplitude quadrupole and octupole shape dynamics, as well as the dynamics of induced fission. Modern implementations of the collective Hamiltonian model are based on the microscopic framework of energy density functionals, that provide an accurate global description of nuclear ground states and collective excitations. Results of illustrative calculations are discussed in comparison with available data.
Comment: 30 pages, 15 figures, Contribution to the "Handbook of Nuclear Physics", Springer, 2022, edited by I. Tanihata, H. Toki and T. Kajino

الوصول الحر: http://arxiv.org/abs/2203.07608Test