Heavy-ion Fusion Reactions Research Articles

Survival probability of Selenium-induced fusion reactions

In this paper, we investigated every potential scenario for selenium-induced heavy ion fusion reactions using astatine isotopes as the target. In this context, we examined [Formula: see text]Se projectiles and [Formula: see text]At targets having longer half-lives of comprising 21 fusion reactions for the synthesis of superheavy element [Formula: see text]. We assessed fusion cross-sections ([Formula: see text]), compound nucleus formation probability ([Formula: see text]), and survival probability ([Formula: see text]) for [Formula: see text]Se projectiles on [Formula: see text]At targets. The evaporation residue cross-sections ([Formula: see text]) is found to be larger for the fusion reaction of [Formula: see text]At of about 14.1[Formula: see text]fb. Hence, these striking results are useful in the synthesis of superheavy element [Formula: see text].

Compound nucleus formation probability of heavy and superheavy nuclei synthesized using heavy ion fusion reactions

The role of entrance channel parameters such as Z2/A, charge asymmetry αz, mass-asymmetry (ηA), charge product (Z1Z2), mean fissility χm, Coulomb interaction parameter and (N−Z)/(N+Z) on compound nucleus formation of actinide nuclei using heavy ion fusion reactions were investigated. For the formation of compound nuclei, the considered atomic number range of the projectile varies between 5≤Z≤14 and the mass number lies between 10≤A≤34. Similarly, the studied target atomic number varies between 78≤Z≤92 and the mass number range is 197≤A≤238. Among these entrance channel parameters, PCN is more systematic for (N−Z)(N+Z), Z2/A and αz. In addition to entrance channel parameters, the Ecm and EBass also play a significant role in the prediction of PCN. The proposed empirical formulae are applicable to the compound nuclei from Fr to Sg. These findings are significant for the PCN prediction from Fr to Sg.

The slopes of sub-barrier heavy-ion fusion excitation functions shed light on the dynamics of quantum tunnelling

Quantum tunnelling plays a crucial role in heavy-ion fusion reactions at sub-barrier energies, especially in the context of nuclear physics and astrophysics. The nuclear structure of the colliding nuclei and nucleon transfer processes represent intrinsic degrees of freedom. They are coupled to the relative ion motion and, in general, increase the probability of tunnelling. The influence of couplings to nucleon transfer channels relatively to inelastic excitations, on heavy-ion fusion cross sections, is one of the still open problems in this field. We present a new analysis of several systems, based on the combined observation of the energy-weighted excitation functions Eσ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sigma $$\\end{document} in relation to their first energy derivatives d(Eσ)/dE\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d(E\\sigma )/dE$$\\end{document}. The relation between d(Eσ)/dE\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d(E\\sigma )/dE$$\\end{document} and Eσ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sigma $$\\end{document} removes the basic differences due to the varying Coulomb barrier when comparing different systems. We show that, depending on the nuclear structure and/or the presence of strong transfer channels, this representation reveals characteristic features below the barrier. The possible presence of cross section oscillations makes this analysis less clear for light- or medium-light systems.

Quantum mechanical treatment of nuclear friction in coupled-channels heavy-ion fusion

Nuclear friction causes energy dissipation in heavy-ion collisions. Its understanding and inclusion in quantum mechanical reaction models are crucial for advancing the physics of heavy-ion reactions forming heavy elements. The effects of nuclear friction on heavy-ion fusion reactions are investigated using the coupled-channels density-matrix method. In this open-quantum-system description, a phenomenological nuclear friction form factor is introduced along with coherent coupled-channels effects. The key nucleus was the 92Zr target, due to its high density of low-lying non-collective excited states, which was recently theorised to be cause of nuclear friction. The calculations using the 16O + 92Zr collision showed that the inclusion of nuclear friction effects increased the fusion probability significantly, and that the agreement between the theoretical and experimental fusion barrier distributions was improved when nuclear friction effects were included.

Probing deformed nuclei: Experimental insights into excited states of 152,153,154Gd isotopes through fusion-evaporation reactions

The rare-earth region has been the focus of various studies aiming at the understanding of nuclear structure and providing information on the details of the reaction mechanism. The Gd isotopes belong to this group of nuclei and despite the available spectroscopic information, several open questions about their structure still exist, such as the inter-band transitions related to shape evolution or branching-ratios in deformed states. In addition, production cross sections of different reactions to Gd isotopes are largely unknown.In this work, we report on an experimental attempt to populate the excited states in the isotopes 152,153,154Gd by employing the heavy-ion fusion reaction 18O+138Ba → 156-xGd + xn in the 58-64 MeV energy range (center-of-mass). The experiment was conducted at the 9 MV FV Pelletron Tandem at the Horia Hulubei National Institute for Physics and Nuclear Engineering, employing the ROSPHERE array. Several branching-ratios for energy levels in 152,153Gd have been measured, offering new and updated values. Furthermore, relative cross sections regarding the fusion-evaporation reactions 138Ba(18O, 4n)152Gd, 138Ba(18O, 3n)153Gd, and 138Ba(18O, 2n)154Gd have been measured and compared with theoretical calculations with PACE4.

Search for beyond-mean-field signatures in heavy-ion fusion reactions

Search for beyond-mean-field signatures in heavy-ion fusion reactions

Transfer learning and neural networks in predicting quadrupole deformation

Abstract Accurately determining the quadrupole deformation parameters of atomic nuclei is crucial for understanding their structural and dynamical properties. This study introduces an innovative approach that combines transfer learning techniques with neural networks to predict the quadrupole deformation parameters of even-even nuclei. With the application of this innovative technique, the quadrupole deformation parameters of 2331 even-even nuclei are successfully predicted within the nuclear region defined by proton numbers \(8 \leq Z \leq 134\) and neutron numbers \(N \geq 8\). Additionally, the study discusses the impact of nuclear quadrupole deformation parameters on the capture cross-sections in heavy-ion fusion reactions, reconstructing the capture cross-sections for the reactions \(^{48}\text{Ca} + ^{244}\text{Pu}\) and \(^{48}\text{Ca} + ^{248}\text{Cm}\). This research offers new insights into the application of neural networks in nuclear physics and underscores the potential of merging advanced machine learning techniques with both theoretical and experimental data, particularly in fields where experimental data is limited.

Analysis of reaction dynamics considering MAD by Langevin equation

In heavy ion fusion and nucleon transfer reactions, which lead to the synthesis of superheavy elements, it is important to understand the reaction mechanisms. The fusion reaction mechanism is analyzed in the case of deformed target nuclei such as actinide target nuclei. We have analyzed the correlation between fission fragment mass and scattering angle (MAD) using the Langevin equation. Taking into account the effect of the collision direction between the projectile and deformed target nuclei, we present the analysis of the experimental data for the MAD of 32S+232Th.

Low-energy fusion hindrance in medium-light systems

Heavy-ion fusion reactions give fundamental information on the quantum tunnelling of many-body systems where several intrinsic degrees of freedom are contributing. Moreover, the existence of hindrance in the fusion of light systems is critical for a variety of stellar environments. Hindrance is often characterised by a maximum of the astrophysical S factor with decreasing energy, and is an interesting link between heavy-ion fusion and astrophysics. The underlying physical background is still under debate. Recently it has been pointed out that the Pauli exclusion principle influences the ion-ion potential and, as a consequence, low-energy fusion hindrance is produced because of the thicker and higher Coulomb barrier. We recently performed systematic investigations on the fusion of several medium-light systems to establish a reliable basis for the extrapolation to the lighter cases of astrophysical interest. The results obtained for 12C + 24,26Mg and 12C + 30Si are discussed here. Hindrance is observed in all cases, however, with differing features, so extrapolating to lighter systems is not straightforward. Additionally, oscillations are observed in the sub-barrier logarithmic slopes of the 12C + 24,26Mg excitation functions, which complicates identifying the hindrance threshold in those two cases. Coupled-channels calculations for all these systems have been performed. The results show that fusion cross sections are well reproduced by simple tunnelling through the potential barrier, at the lowest energies. An alternative way to represent the data is discussed, which helps identifying the various channel couplings.

Generation of fusion and fusion-evaporation reaction cross-sections by two-step machine learning methods

In order to obtain cross-sections of heavy-ion fusion and fusion-evaporation reactions, artificial neural networks, cubist, random forest, support vector regression, extreme gradient boosting, and multiple linear regression machine learning approaches were used separately in this study. The outcomes from these different methods that are obtained from the training carried out with the existing experimental data in the literature were compared. Furthermore, it has been observed that a two-step process yielded better results for determining the heavy-ion reaction cross-sections, after first estimating which approach would be better for which reaction. In this manner, the method for which the cross-section needs to be calculated is determined by the machine learning classification application, and predictions can be made using the machine learning regression application with the determined method. It has been concluded that the obtained results are in harmony with the experimental data and that the methods can be used safely. The obtained results are published on a web page that allows for online calculation of heavy-ion fusion and fusion-evaporation reaction cross-sections.

Fabrication and characterization of thin [formula omitted]Sn films for heavy-ion nuclear reaction measurements

The fabrication of thin isotopically enriched 120,124Sn targets have been presented. The thin film targets prepared have been used in nuclear physics experiments to apprehend the heavy-ion fusion and multi-nucleon transfer reaction dynamics around the Coulomb barrier. Vacuum evaporation viz. resistive heating technique has been used for the fabrication of the targets with varying areal densities in the range of 50–250 μg/cm2 backed with a carbon layer of ≈20μg/cm2 using a nominal amount of 30 mg isotopically enriched material. The fabricated targets have been characterized using multiple advanced techniques viz. Energy Dispersive X-ray Spectroscopy (EDS), Scanning Electron Microscopy (SEM), and X-ray Diffractometry (XRD). The thickness of the targets has been measured using Rutherford Back-scattering Spectrometry (RBS). The isotopic contamination levels have been ascertained with an in-beam experiment using Heavy Ion Reaction Analyzer at IUAC, New Delhi.

Impact of density dependence of symmetry energy on astrophysical S-factor for heavy-ion fusion reactions

Impact of density dependence of symmetry energy on astrophysical S-factor for heavy-ion fusion reactions

Effect of low lying vibrational and rotational energy levels on the fusion cross-sections

In heavy-ion fusion reactions, the coupling of various degrees of freedom to the relative motion leads to an enhancement in the sub-barrier fusion cross-section compared to the 1-dimensional barrier penetration model. The present work aims to explore the exclusive effect of low-lying vibrational and rotational energy levels in the enhancement of cross-sections for 12C induced reactions at the energy below and around the Coulomb barrier using the CCFULL code. The results show that for the negative and positive values of β4, the rotational energy states up to 2+ and 6+ significantly contributed to the fusion cross-sections which leads to fusion enhancement. These results can be useful for better understanding the dynamics of heavy-ion fusion reactions.

Recent experimental results in sub- and near-barrier heavy ion fusion reactions (2nd edition)

Recent experimental results in sub- and near-barrier heavy ion fusion reactions (2nd edition)

Empirical model for compound nucleus formation probability in heavy ion fusion reactions

Empirical model for compound nucleus formation probability in heavy ion fusion reactions

Effect of Diffuseness Parameter on the Fusion Cross-Section of Closed-Shell Nuclei

Heavy-ion fusion reactions are important and essential to express the dynamical properties of colliding nuclei, and to address the tunneling effect in quantum mechanics. In the fusion process, the ion-ion potential plays an important role in approaching the measured cross section with the experimental value by influencing the tunneling probability of interacting nuclei. In this work, the fusion cross-sections of closed-shell heavy-ion fusion systems have been calculated and analyzed in the framework of coupled channel theory, using the code CCFULL, by fixing the potential depth value = 102.9 MeV and the fusion radius = 1.096 , while, the diffuseness parameter of Wood--Saxon potential is varied from 0.6 to 1.1 to fitting the fusion cross-section data at energies near and below the Coulomb barrier. It was observed that our approach is able to estimating the experimentally observed cross-sections of closed-shell colliding nuclei.

Systematic study of fusion barriers with energy dependent barrier radius

Considering energy dependence of the barrier radius in heavy-ion fusion reactions, a modified Siwek-Wilczyński (MSW) fusion cross section formula is proposed. With the MSW formula, the fusion barrier parameters for 367 reaction systems are systematically extracted, based on 443 datasets of measured cross sections. We find that the fusion excitation functions for about 60% reaction systems can be better described by introducing the energy dependence of the barrier radius which is due to the dynamical effects at energies near and below the barrier. Considering both the influence of the geometry radii and that of the reduced de Broglie wavelength of the colliding nuclei, the barrier heights are well reproduced with only one model parameter. The extracted barrier radius parameters linearly decrease with the effective fissility parameter, and the width of the barrier distribution relates to the barrier height, as well as the reduced de Broglie wavelength at energies around the Coulomb barrier.

Sub-barrier fusion hindrance and absence of neutron transfer channels

The sub-barrier fusion hindrance has been observed in the domain of very low energies of astrophysical relevance. The measured fusion cross sections can be well estimated by using formula obtained by folding a Gaussian function for barrier height distribution with the expression for classical fusion cross section for fixed barrier. The parameters of the formula vary smoothly implying its usage in estimating the excitation function. In the present work, the effects of deformation and transfer on fusion reactions have been studied and the absence of neutron transfer channels has been correlated to the hindrance in heavy-ion fusion reactions.

Decay Times of Compound Nuclei in Heavy Ion Fusion Reactions

The decay time of the compound nuclei has been studied using different statistical models. In the present work, we have improved the back-shifted microscopic level density model by including the pairing effect, an angular momentum-dependent moment of inertia, fission barriers, and a dynamical effect. The decay time of the compound nuclei is evaluated with and without dynamical effect and also compared with various statistical models and available experiments. It is also observed that the decay times of the compound nuclei formed during inverse kinematics is found to be larger when compared to direct kinematics at same excitation energy. Furthermore, the possible fission fragments have been identified using modified generalised liquid drop model. The identified fission fragments are compared with available experiments. The failure of the experiments to synthesize the superheavy element Z = 119 and 120 may be confirmed by the identification of fission fragments in these reactions. The predicted decay times of the compound nuclei and possible fission fragments gives a complete over view of failure of reactions to synthesize the superheavy element Z = 119 and 120.

Effect of entrance channel parameters on compound nucleus formation probability in heavy ion fusion reactions

To study the role of entrance channel parameters on compound nucleus formation probability (Pcn), we have picked up 92 heavy ion fusion reactions forming superheavy nuclei and classified them into four categories based on deformation parameters of projectile and target nuclei such as spherical-spherical, spherical-deformed, deformed-spherical, and deformed-deformed. Next, we have examined the role of entrance channel parameters on Pcn for each category and found that the mean fissility parameter plays the strongest role for all the categories. Finally, the effect of the projectile energy in the centre of mass frame has been taken into account to construct four empirical formulae for the four categories. We believe the proposed empirical formulae can be very useful in the planning of experiments in synthesizing the superheavy elements.