arXiv subjects

Long Zhu

Publications and source records attributed to Long Zhu.

At least 19 recordsLinked to original sources

arXiv2026

Purifying one-neutron removal as a probe of single-particle strength

One-neutron removal reactions exhibit a strong proton-neutron asymmetry dependence in the inclusive reduction factor $R_s$, a long-standing issue that has been discussed in terms of both possible intrinsic isospin dependence of single-particle strength and reaction-mechanism effects. We address this issue by reframing inclusive removal as a coupled fast-dynamics and deexcitation process, and by validating this transport-deexcitation chain against a global, mutually constraining data set. Confronting 73 one-neutron removal cross sections and 28 residue parallel-momentum distributions with isospin-dependent quantum molecular dynamics followed by GEMINI evaporation shows that the apparent $R_s$-$\Delta S$ trend is correlated with evaporation feeding and evaporation loss. By subtracting the feeding contribution and correcting for the loss component in the measured cross sections, we construct a purified reduction factor $R_{\rm dir}$, that more closely reflects single-particle strength than the inclusive $R_s$. The resulting $R_{\rm dir}$ exhibits a much weaker $\Delta S$ dependence within current uncertainties, consistent with the weak isospin-asymmetry dependence observed in nucleon-transfer and quasifree-knockout systematics.

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arXiv2026

New perspective on cold fusion reactions: A microscopic description

A microscopic framework that combines the Hartree-Fock-Bogoliubov (HFB) approach with the fusion by diffusion (FBD) model is proposed to investigate the synthesis mechanism of superheavy nuclei (SHN). For the reaction $^{48}\text{Ca}+^{208}\text{Pb}$, the calculated evaporation-residue cross section (ERCS) reproduces the experimental data reasonably well. The method enables self-consistent extraction of the fusion injection point and inner barrier from HFB potential-energy surfaces (PES), thereby incorporating nuclear structure effects while eliminating phenomenological tuning at the fusion stage. For cold-fusion reactions, the PES features a hyperasymmetric valley driven by shell effects. This $^{208}$Pb anchored valley connects the entrance channel to compound nucleus formation and provides an exit channel for cluster decay. We further investigate the cold-fusion reactions $^{54}\text{Cr}+^{208}\text{Pb}$ and $^{58}\text{Fe}+^{208}\text{Pb}$, obtaining a near-exponential decrease of $P_{\text{CN}}$ with compound-nucleus charge $Z$, consistent with established systematics. This approach demonstrates a self-consistent framework that can reduce uncertainties in the fusion stage of SHN production.

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arXiv2025

Determination of nuclear deformations with an emulator for sub-barrier fusion reactions

Based on the eigenvector continuation, which is mathematically an instance of the reduced basis method (RBM), we construct an emulator for coupled-channels calculations for heavy-ion fusion reactions at energies around the Coulomb barrier. We apply this to the $^{16}$O+$^{144,154}$Sm, $^{186}$W reactions and examine whether the emulator can be used to extract the deformation parameters of the target nuclei. We show that the emulator not only accelerates the calculations but also has an ability to accurately extract the nuclear shapes. This indicates that the emulator provides a powerful tool to systematically explore intrinsic shapes of atomic nuclei, enhancing our understanding of the fundamental properties of nuclear systems.

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arXiv2025

Mechanism of the quasi-elastic scattering based on the dinuclear system concept

A unified description of full reaction channels in low-energy heavy-ion collisions is a great challenge. Although the theoretical models based on the dinuclear system (DNS) concept have been successfully employed in multinucleon transfer (MNT) reactions, the underestimation of the quasi-elastic (QE) channel results in unreliable description of few nucleon transfer, especially for the light reaction systems. In this work, the DNS-sysu model is improved by introducing the impact-parameter-dependent transition probabilities for a unified description of few nucleon and many nucleon transfer in MNT reactions. Extensive experimental data -- including reactions such as 40Ca, 58Ni, 64Ni, 136Xe, and 208Pb + 208Pb -- were compared with the model predictions. The calculated isotopic distributions, mass distributions, and charge distributions show good agreement with experimental measurements. The improved DNS-sysu model enables reasonable characterization and description of the QE/grazing collisions, notably resolving long-standing underestimation in the QE channel.

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arXiv2025

Role of two-body dissipation on the mean-field dynamics validity

The role of two-body dissipation in nuclear reactions at energies of several times Coulomb barrier remains unclear but is crucial for understanding the mechanisms of deep-inelastic reactions. In this letter, we report a systematic analysis of two-body dissipation effects on the validity of mean-field dynamics, enabled by the TDHF-QRx approach, which incorporates the collision term via the relaxation-time approximation rather than full collision calculations. For deep-inelastic reactions, the contact time between nuclei is found to increase, resulting in changes to the reaction process and fragment properties such as scattering angles and total kinetic energy. These changes become important with the increase of reaction energy and decrease of impact parameter. We identify the range of reaction condition where two-body dissipation becomes significant, providing valuable insights for the applicability of mean-field dynamics approaches. The limitations of model, particularly those arising from the incomplete conservation of the locality of two-body dissipation within the quantum framework, are also discussed.

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arXiv2025

Concentrated valence nucleons transfer in heavy-ion collisions: implications for questing the stable superheavy elements

The multinucleon transfer process is regarded as a promising pathway for producing the stable superheavy elements. However, the underlying mechanism, especially the possible transfer channels for sailing to the ``island of stability'' are poorly known. In this work, the time-dependent Hartree-Fock theory is used to investigate the collision dynamics of $^{136}$Xe, $^{198}$Pt, $^{238}$U + $^{238}$U reactions. A novel reaction channel of the concentrated valence nucleons (CVN) transferring is found in the collisions heading on the tips of $^{238}$U. These nucleons are transferred with relatively short relaxation time and break the symmetry of nucleon exchange in the early reaction stage. In consequence, the mass equilibrium with relaxation time is deviated from the systematic behavior based on the macroscopic-microscopic potential energy surface. The CVN transfer channel shows promising prospect for producing neutron-rich superheavy nuclei. In this case, we also investigated the angular distributions of products from the CVN transfer channel in the reaction $^{238}$U + $^{238}$U with Tip-Side configuration, and the optimal detection angles are predicted.

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arXiv2025

Synthesis of the superheavy elements beyond Og: extrapolating from ${}^{48}\mathrm{Ca}$ to ${}^{54}\mathrm{Cr}$

Theoretical predictions on the optimal reaction energies are essential for producing superheavy elements (SHEs) beyond Og. Due to the limitation of the targets, synthesizing elements 119 and 120 will require beams of ${}^{50}\mathrm{Ti}$ and/or ${}^{54}\mathrm{Cr}$ ions. However, is it reliable to theoretically extrapolate from the well-investigated ${}^{48}\mathrm{Ca}$ induced reactions to those with heavier projectiles? In this work, we apply the Fusion-by-Diffusion (FBD) concept to answer this question from two perspectives: radial and mass asymmetry degrees of freedom. The FBD concept is employed in the mass asymmetry degree of freedom for the first time, in which by fitting the calculations to experimental evaporation residue cross sections (ERCS) for the reactions of ${}^{48}\mathrm{Ca}$ as projectiles with the actinide targets, a strong linear correlation between the contact distance ($D_\mathrm{cont}$) and center-of-mass energy excess above the Coulomb barrier ($E_\mathrm{c.m.}-B_0$) is found and a parametrization of the $D_\mathrm{cont}$ is introduced. Using the result of parametrization, the calculations satisfactorily reproduce the shapes of all hot fusion excitation functions and values of the ERCS. Furthermore, thanks to the recent experimental data, we extrapolate the calculation in the reactions ${}^{50}\mathrm{Ti}+{}^{242}\mathrm{Pu}$, ${}^{50}\mathrm{Ti}+{}^{244}\mathrm{Pu}$, and ${}^{54}\mathrm{Cr}+{}^{238}\mathrm{U}$. The calculations reproduce the experimental data rather well within the experimental errors in both perspectives. Our results demonstrate that there is no non-negligible systematic deviation in extrapolating the projectiles from $^{48}\text{Ca}$ to $^{50}\text{Ti}$ and $^{54}\text{Cr}$ for synthesizing SHEs beyond Og.

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arXiv2025

Time-dependent random phase approximation for particle-number fluctuations and correlations in deep-inelastic collisions of $^{144}$Sm+$^{144}$Sm and $^{154}$Sm+$^{154}$Sm

The fluctuation-dissipation mechanism underlying non-equilibrium transport in low-energy heavy-ion reactions remains unclear. Although the time-dependent Hartree-Fock (TDHF) method provides a reasonable description of average reaction outcomes and one-body dissipation, it is known to significantly underestimate fluctuations of observables. The purpose of this work is to investigate deep-inelastic collisions of 144Sm+144Sm and 154Sm+154Sm with microscopic mean-field approaches and to show a predominant role of one-body dissipation as well as one-body fluctuations and correlation in low-energy heavy-ion reactions. Three dimensional TDHF calculations are carried out for 144Sm+144Sm at Ecm=500 MeV and 154Sm+154Sm at Ecm=485 MeV for a range of impact parameters with Skyrme SLy5 energy density functional. Backward time evolutions are performed as well to evaluate fluctuations and correlation in nucleon numbers within time-dependent random phase approximation (TDRPA). With TDRPA we calculate mass- and charge-number fluctuations, as well as the correlation between neutron and proton transfers, for each impact parameter. We demonstrate that TDRPA quantitatively reproduces the experimental \sigma_{AA}^2-TKEL distributions, whereas it systematically underestimates the charge fluctuation, \sigma_{ZZ}. The double-differential cross sections of reaction products are calculated, showing good agreement with the experimental data. We confirm a long-thought characteristic property that the closed-shell structure limits nucleon transfer at small energy losses, based on our microscopic TDHF and TDRPA calculations.

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arXiv2024

Medium recoil mode of $\Delta$ production in single isobaric charge-exchange reactions

The dynamic mechanisms underlying single charge-exchange reactions have been investigated using a theoretical framework that combines the Isospin-dependent Quantum Molecular Dynamics (IQMD) model with the statistical decay model GEMINI++. Two distinct channels contribute to the single isobaric charge-exchange reaction: quasi-elastic channel, where neutron-proton scattering drives the charge-exchange, and inelastic channel, where the $\Delta$ particle is produced during the process. In a referenced study [Phys.RevC 106.014618(2022)], experimental data have revealed that the inelastic channel accounts for approximately 50 percent of the single isobaric charge-exchange reaction. However, our current model fails in reproducing the significant contribution of inelastic channel unless the novel medium recoil mode associated with $\Delta$ production is considered in the calculations. Notably, this in-medium effect arising from inelastic nucleon-nucleon collisions is not yet incorporated into mainstream microscopic transport models. The dynamical properties of protons and pions emitting in the single isobaric charge-exchange reactions are predicted. This exploration of in-medium effects adds a valuable dimension to our understanding of the intricate dynamics involved in single charge-exchange reactions.

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arXiv2024

Effects of incompressibility on the neutron-proton equilibration in $^{70}$Zn + $^{70}$Zn collisions at 35 MeV/nucleon

Background: The primary goal of studying isospin dynamics via heavy-ion reactions is to explore the isospin dependence of effective interactions within the nuclear equation of state (EOS). Purpose: This work aims to investigate the effects of nuclear incompressibility ($ K_0 $) on neutron-proton equilibration in projectile-like fragments (PLFs). Method: We simulate $^{70}$Zn + $^{70}$Zn collisions at 35 MeV/nucleon using the isospin-dependent quantum molecular dynamics (IQMD) model, coupled with the statistical decay code GEMINI. Results: The IQMD simulations not only reproduce experimental data patterns but also reveal the dynamic mechanisms underlying the binary breakup of PLFs. The rotation of PLFs is influenced by the transformation of angular momentum, which is connected to the isoscalar component of the EOS. This connection explains why shifts in $ K_0 $ affect the description of neutron-proton equilibration as measured by PLF rotation. The simulations demonstrate that a model with a smaller $ K_0 $ paired with a softer symmetry energy, or a larger $ K_0 $ with a slightly stiffer symmetry energy, both offer better indications of neutron-proton equilibration. Conclusion: Considering the uncertainty in $ K_0 $, the slope of the symmetry energy is constrained within the range of $ L = 20 \sim 40 $ MeV, providing valuable insights into the nuclear equation of state.

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arXiv2024

New insight into the N/Z and mass equilibration in heavy-ion collisions

The dynamics of N/Z and mass equilibration are investigated in the reactions 112,124Sn + 239Pu by employing the isospin-dependent quantum molecular dynamics model. It is found that N/Z and mass equilibration take place at different collision stages. The N/Z relaxation is observed in the approaching phase (from first contact to deepest contact) with a very short time, whereas interestingly we find for the first time that mass equilibration only takes place in the separation phase (from the deepest contact to re-separation), which are explained by investigating the dynamical asymmetry between the approaching and separation phases. The mass equilibration also could be clarified with a dynamical potential energy surface. Our results provide a new insight into the equilibration dynamics of the quantum systems.

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arXiv2024

Quantifying angular distributions in multinucleon transfer reactions with a semi-classical method

The multinucleon transfer (MNT) process in low-energy heavy ion collisions can be utilized to produce unknown nuclei far beyond the stability line. However, the reaction products exhibit broad angular and energy distributions, which could lower the experimental detection efficiency. We present a classical approach that employs a parameterized angular distribution to describe the complex issue. By analyzing limited experimental data on angular distribution, we proposed a three-parameter formula to calculate the angular distribution and identified the dependencies of the parameters. We also discuss the sensitivity of these parameters within this method. A comprehensive comparison with microscopic models and experimental data across a wide range of conditions is conducted. The proposed formula offers an efficient and straightforward way to determine the angular distribution of MNT products.

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arXiv2024

Bayesian uncertainty quantification for synthesizing superheavy elements

To improve the theoretical prediction power for synthesizing superheavy elements beyond Og, a Bayesian uncertainty quantification method is employed to evaluate the uncertainty of the calculated evaporation residue cross sections (ERCS) for the first time. The key parameters of the dinuclear system (DNS) model, such as the diffusion parameter $\textit{a}$, the damping factor $E_\mathrm{d}$, and the level-density parameter ratio $a_\mathrm{f}/a_\mathrm{n}$ are systematically constrained by the Bayesian analysis of recent ERCS data. One intriguing behavior is shown that the optimal incident energies (OIE) corresponding to the largest ERCS weakly depend on the fission process. We also find that these parameters are strongly correlated and the uncertainty propagation considering the parameters independently is not reasonable. The 2$\sigma$ confidence level of posterior distributions for $a = 0.586_{-0.002}^{+0.002}$ fm, $E_\mathrm{d} = 25.65_{-3.41}^{+3.43}$ MeV, and $a_\mathrm{f}/a_\mathrm{n} = 1.081_{-0.021}^{+0.021}$ are obtained. Furthermore, the confidence levels of the ERCS and OIE for synthesizing Z = 119 via the reactions($^{54}\mathrm{Cr}+^{243}\mathrm{Am}$), (${}^{50}\mathrm{Ti}+{}^{249}\mathrm{Bk}$), and (${}^{51}\mathrm{V}+{}^{248}\mathrm{Cm}$) are predicted. This work sets the stage for future analyses to explore the OIE and reaction systems for the synthesis of superheavy elements.

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arXiv2024

Microscopic study of deformation and orientation effects in heavy-ion reactions above Coulomb barrier using the Boltzmann-Uehling-Uhlenbeck model

Background: The understanding of the impact of initial deformation and collision orientation on quasi-fission and fusion-fission reactions remains incomplete. Purpose: This article aims to explore how the orientation of deformed nuclei influences quasi-fission and fusion-fission around 1.2 VB, employing a micro dynamical method in systems with diverse shapes, namely 24Mg + 178Hf, 34S + 168Er, and 48Ti + 154Sm. Method: Utilizing the Boltzmann-Uehling-Uhlenbeck model, this study investigates quasi-fission and fusion fission reactions. The model elucidates micro-dynamic processes and microscopic observables through the definition of the window and event-by-event simulations. Results: The findings reveal that the orientation of deformed nuclei significantly influences the nucleus-nucleus interaction potential, thereby impacting the competition between quasi-fission and fusion-fission. Particularly, the orientation of the deformed target nucleus emerges as the primary factor affecting this competition. Notably, a higher proportion of fusion-fission events is observed when the target nucleus is in the belly orientation compared to the tip. The study also observes that the configuration of the dinuclear system contributes to fluctuations and dissipation. Collisions with different orientations result in distinct dinuclear system configurations, with belly-oriented collisions leading to larger fluctuations between events, while tip-oriented collisions exhibit smaller fluctuations. Conclusions: Considering diverse orientations of nuclei with distinct initial deformations, this study concludes that the orientation of the target nucleus is the key factor influencing quasi-fission and fusion-fission reactions around 1.2 VB.

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arXiv2024

Shell effects on the drift and fluctuation in multinucleon transfer reactions

This study employs the dinuclear system model (DNS-sysu) to investigate drift and fluctuation mechanisms in 136Xe + 209Bi collisions above the Coulomb barrier. The DNS-sysu model demonstrated its effectiveness in providing reasonable descriptions of drift and fluctuation dynamics for the multinucleon transfer reaction at low energies. We observe temperature-induced changes in the shell effect, impacting nucleon transfer. At higher energies, the weakening constraint of the potential energy surface leads to a reversal in the evolution direction. Additionally, the consideration of shell corrections notably affects fragment distribution at low energies but diminishes for high-energy conditions. This research provides valuable insights into understanding the macroscopic manifestation of nucleon transfer in the multinucleon transfer reaction.

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arXiv2023

Role of the isospin diffusion on cluster transfer in $^{12,14}$C + $^{209}$Bi reactions

Heavy-ion collisions at near-barrier energies provide a crucial pathway for investigating nucleon correlations and clustering structures. Recent experimental results showed that the valence neutrons in light projectiles obviously enhance the $\alpha$ transfer. This finding is extremely puzzled and fascinating, because it violates the ground-state $Q$ value systematics unexpectedly. In this work, the time-dependent Hartree-Fock approach is utilized to investigate the cluster transfer. By comparing the reactions $^{12,14}$C + $^{209}$Bi, we discover that above puzzling behavior is because of the strong correlation between isospin diffusion and clustering. Our calculations clearly show that the equilibrium of neutron-to-proton ratio strongly inhibits the clustering. This work opens a prospect for investigating the clustering in open quantum system.

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arXiv2023

Importance of physical information on the prediction of heavy-ion fusion cross section with machine learning

In this work, the Light Gradient Boosting Machine (LightGBM), which is a modern decision tree based machine-learning algorithm, is used to study the fusion cross section (CS) of heavy-ion reaction. Several basic quantities (e.g., mass number and proton number of projectile and target) and the CS obtained from phenomenological formula are fed into the LightGBM algorithm to predict the CS. It is found that, on the validation set, the mean absolute error (MAE) which measures the average magnitude of the absolute difference between $log_{10}$ of the predicted CS and experimental CS is 0.129 by only using the basic quantities as the input, this value is smaller than 0.154 obtained from the empirical coupled channel model. MAE can be further reduced to 0.08 by including an physical-informed input feature. The MAE on the test set (it consists of 280 data points from 18 reaction systems that not included in the training set) is about 0.19 and 0.53 by including and excluding the physical-informed feature, respectively. We further verify the LightGBM predictions by comparing the CS of $^{ 40,48}{\rm Ca }$+$^{78}{\rm Ni}$ obtained from the density-constrained time-dependent Hartree-Fock approach. Our study demonstrates the importance of physical information in predicting fusion cross section of heavy-ion reaction with machine learning.

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arXiv2023

Constraining the Woods-Saxon potential in fusion reactions based on the neural network

The accurate determination of the nuclear interaction potential is essential for predicting the fusion cross sections and understanding the reaction mechanism, which plays an important role in the synthesis of superheavy elements. In this work, the neural network, which combines with the calculations of the fusion cross sections via the Hill-Wheeler formula, is developed to optimize the parameters of the Woods-Saxon potential by comparing the experimental values. The correlations between the parameters of Woods-Saxon potential and the reaction partners, which can be quantitatively fitted to a sigmoid-like function with the mass numbers, have been displayed manifestly for the first time. This study could promote the accurate estimation of nucleus-nucleus interaction potential in low energy heavy-ion collisions.

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