Structure Of Light Nuclei Research Articles

Inelastic scattering reaction as a probe for monopole, dipole and quadrupole excitations

The study of collective motions within atomic nuclei, such as monopole, dipole, and quadrupole excitations, is crucial for understanding nuclear structure and properties, which provide insights into the spatial distribution and dynamic nature of protons and neutrons in nuclei. By analyzing the angular distributions of these modes excited via inelastic scattering reactions, we can determine the transition characteristics and deformation lengths of nuclei. Specific case studies, including quadrupole excitations and dipole excitations indicating exotic cluster structures in light nuclei, highlight the utility of modern experimental setups like the solenoidal spectrometer and the active target detector.

Test experiment to determine the time distribution of the background between MMF accelerator pulses on the RADEX channel

The authors offer works using the MMF INR RAS neutron channel to study the cluster structures in light nuclei, in particular, 𝛼-4n-𝛼 and 8Be-4n in the highly excited state 12Be*. This needs the registration of charged particles from the 12Be* 𝛽-decay during its formation in the 𝑛+13C reaction in the intervals between cascade neutron pulses. The paper presents the first results of an experiment on measuring the spectra and time distributions of gamma-quanta and neutrons using a proton beam of 50 Hz and a duration of 0.3 𝜇s.

Topical collection on light clusters in nuclei and nuclear matter: nuclear structure and decay, heavy-ion collisions, and astrophysics

Recent progress to treat clustering in nuclear systems has an impact to different branches of nuclear theory. Numerical methods as well as many-body theory (Green-function methods) have been worked out to describe few-body clusters in a nuclear environment where medium effects, in particular the antisymmetrization of the wave function (Pauli blocking) are of relevance. Nuclear structure (Hoyle – like states), nuclear reactions, and consequences for astrophysics (neutron stars, supernova explosions) are emerging applications. The main topics were (1) Cluster models, structure of light nuclei, cluster quantum phase transition; (2) Reaction theory, \(\alpha \)-decay of heavy and superheavy nuclei; (3) Clustering in nuclear matter and consequences for thermodynamic properties (4) Heavy-ion collisions and clustering in nonequilibrium systems, transport codes; (5) Astrophysical consequences of clustering.

Possibility of deformed dual bubble-like structure in light nuclei

Possibility of deformed dual bubble-like structure in light nuclei

Flow in collisions of light nuclei

In this talk we discuss several interesting aspects of collective flow in small systems in reference to planned future experiments. First, we bring in the novel possibility of exploring elliptic flow with heavy nuclei collisions on polarized deuteron targets, accessible in AFTER@LHC program after Long Shutdown 3. Then we discuss the Glauber model predictions for the presently considered 16O −16O program at RHIC and the LHC. Finally, we turn to our previous proposal concerning specific flow signatures of intrinsic correlations (such as the predicted α clusterization) in the structure of light nuclei in collisions with heavy nuclei. In particular, 12C–heavy nucleus ultrarelativistic reactions would provide insight into the ground-state 12C structure, complementary to traditional nuclear structure measures.

Signatures of α -clustering in O16 by using a multiphase transport model

$\alpha$-clustered structures in light nuclei could be studied through "snapshots" taken by relativistic heavy-ion collisions. A multiphase transport (AMPT) model is employed to simulate the initial structure of collision nuclei and the proceeding collisions at center of mass energy $\sqrt{s_{NN}}$ = 6.37 TeV. This initial structure can finally be reflected in the subsequent observations, such as elliptic flow ($v_{2}$), triangular flow ($v_{3}$) and quadrangular flow ($v_4$). Three sets of the collision systems are chosen to illustrate system scan is a good way to identify the exotic $\alpha$-clustered nuclear structure, case I: $\mathrm{^{16}O}$ nucleus (with or without $\alpha$-cluster) + ordinary nuclei (always in Woods-Saxon distribution) in most central collisions, case II: $\mathrm{^{16}O}$ nucleus (with or without $\alpha$-cluster) + $\mathrm{^{197}Au}$ nucleus collisions for centrality dependence, and case III: symmetric collision systems (namely, $^{10}$B + $^{10}$B, $^{12}$C + $^{12}$C, $^{16}$O + $^{16}$O (with or without $\alpha$-cluster), $^{20}$Ne + $^{20}$Ne, and $^{40}$Ca + $^{40}$Ca) in most central collisions. Our calculations propose that relativistic heavy-ion collision experiments at $\sqrt{s_{NN}}$ = 6.37 TeV are promised to distinguish the tetrahedron structure of $\mathrm{^{16}O}$ from the Woods-Saxon one and shed lights on the system scan projects in experiments.

He8 and Li9 cluster structures in light nuclei

The possibility of the $^8$He and $^{9}$Li clusters in atomic nuclei is discussed. Until now most of the clusters in the conventional models have been limited to the closures of the three-dimensional harmonic oscillators, such as $^4$He, $^{16}$O, and $^{40}$Ca. In the neutron-rich nuclei, however, the neutron to proton ratio is not unity, and it is worthwhile to think about more neutron-rich objects with $N>Z$ as the building blocks of cluster structures. Here the nuclei with the neutron number six, which is the subclosure of the $p_{3/2}$ subshell of the $jj$-coupling shell model, are assumed to be clusters, and thus we study the $^8$He and $^9$Li cluster structures in $^{16}$Be ($^8$He+$^8$He), $^{17}$B ($^8$He+$^9$Li), $^{18}$C ($^9$Li+$^9$Li), and $^{24}$C ($^8$He+$^8$He+$^8$He). Recent progress of the antisymmetrized quasi cluster model (AQCM) enables us to utilize $jj$-coupling shell model wave functions as the clusters rather easily. It is shown that the $^8$He+$^9$Li and $^9$Li+$^9$Li cluster configurations cover the lowest shell-model states of $^{17}$B and $^{18}$C, respectively. To predict the cluster states with large relative distances, we increase the expectation value of the principal quantum numbers by adding the nodes to the lowest states under the condition that the total angular momentum is unchanged (equal to $J^\pi =0$). As a result, developed cluster states are obtained around the corresponding threshold energies. The rotational band structure of $^{24}$C, which reflect the symmetry of equilateral triangular configuration ($D_{3h}$ symmetry) of three $^8$He clusters, also appears around the threshold energy.

Alpha-clustering effects in heavy nuclei

The study of cluster structures in light nuclei is extending to the heavy nuclei in these years. As for the stable N = Z nuclei, from the lighter 8Be, 12C nuclei to the heavier 20Ne and even the 40Ca and 44Ti medium nuclei, the α cluster structures have been well studied and confirmed. In heavy nuclei, due to the dominated mean field, the existence of α cluster structure is not clear as light nuclei but some clues were found for indicating the core+α cluster structure in some nuclei, in particular, the 208Pb+α structure in 212Po. We review some recent progress about the theoretical and experimental explorations of the α-clustering effects in heavy nuclei. We also discuss the possible α cluster structure of heavy nuclei from the view of α decay.

Transverse momentum dependent quark and gluon distributions of light nuclei

We investigate the unpolarized transverse momentum dependent (TMD) structure of light nuclei in the modified chiral quark exchange model (QEM), for the first time. To this end, we calculate the TMD quark and gluon distributions inside the bound state nucleons of the light nuclei based on the modified chiral quark model in which the TMD bare quark distributions of the bounded nucleons are needed. In order to compute these bare distributions, we first obtain the bare quark momentum densities using the QEM and then calculate the TMD bare distributions applying a theoretical method in which the light-cone variables are used. Finally, considering the nucleon structure of helium, tritium and deuteron nuclei, we obtain their TMD quark and gluon densities at low Q2 scale. It is shown that our results have appropriate properties that are expected for the TMD distribution functions.

High-voltage power supply system for detecting equipment of DSS experiment at JINR Nuclotron

The eight-channel high-voltage power supply system based on using the Wenzel Elektronik N1130 module is described. The characteristics of 8DAC-12 and 8ADC-14 types control modules of CAMAC standard designed for high-voltage systems are presented. This system was successfully used to provide the power supply of scintillation detectors in the experiments on the study of the structure of light nuclei at JINR Nuclotron.

Nucleon localization and fragment formation in nuclear fission

An electron localization measure was originally introduced to characterize chemical bond structures in molecules. Recently, a nucleon localization based on Hartree-Fock densities has been introduced to investigate $\alpha$-cluster structures in light nuclei. Compared to the local nucleonic densities, the nucleon localization function has been shown to be an excellent indicator of shell effects and cluster correlations. Using the spatial nucleon localization measure, we investigate the emergence of fragments in fissioning heavy nuclei. To illustrate basic concepts of nucleon localization, we employ the self-consistent energy density functional method with a quantified energy density functional optimized for fission studies. We study the particle densities and spatial nucleon localization distributions along the fission pathways of $^{264}$Fm, $^{232}$Th and $^{240}$Pu. We demonstrate that the fission fragments are formed fairly early in the evolution, well before scission. We illustrate the usefulness of the localization measure by showing how the hyperdeformed state of $^{232}$Th can be understood in terms of a quasimolecular state made of $^{132}$Sn and $^{100}$Zr fragments. Compared to nucleonic distributions, the nucleon localization function more effectively quantifies nucleonic clustering: its characteristic oscillating pattern, traced back to shell effects, is a clear fingerprint of cluster/fragment configurations. This is of particular interest for studies of fragment formation and fragment identification in fissioning nuclei.

Evidence for survival of theαcluster structure in light nuclei through the fusion process

Background: Despite the importance of light-ion fusion in nucleosynthesis, a limited amount of data exist regarding the de-excitation following fusion for such systems.Purpose: To explore the characteristics of $\ensuremath{\alpha}$ emission associated with the decay of light fused systems at low excitation energy.Method: $\ensuremath{\alpha}$ particles were detected in coincidence with evaporation residues (ER) formed by the fusion of $^{18}\mathrm{O}$ and $^{12}\mathrm{C}$ nuclei. Both $\ensuremath{\alpha}$ particles and ERs were identified on the basis of their energy and time-of-flight. ERs were characterized by their energy spectra and angular distributions while the $\ensuremath{\alpha}$ particles were characterized by their energy spectra, angular distributions, and cross sections.Results: While the energy spectra and angular distributions for the $\ensuremath{\alpha}$ particles are relatively well reproduced by the statistical model codes, evapor and pace4 the measured cross section is substantially underpredicted by the models. Examination of the relative $\ensuremath{\alpha}$ emission probability for similar systems reveals that this underprediction is a more general feature of such light-ion reactions.Conclusion: Comparison of the measured relative $\ensuremath{\alpha}$ cross section at low ${E}_{\mathrm{c}.\mathrm{m}.}$ for $^{18}\mathrm{O}+^{12}\mathrm{C},\phantom{\rule{0.16em}{0ex}}^{16}\mathrm{O}+^{12}\mathrm{C}$, and $^{16}\mathrm{O}+^{13}\mathrm{C}$ indicates that the $\ensuremath{\alpha}$ cluster structure of the initial projectile and target nuclei influences the $\ensuremath{\alpha}$ emission following fusion. The underprediction of the relative $\ensuremath{\alpha}$ emission by the statistical model codes emphasizes that the failure of these models to account for $\ensuremath{\alpha}$ cluster structure is significant.

Symmetry-adapted ab initio no-core shell model calculations for 12C

Symmetry-adapted no-core shell-model calculations reveal dominant symmetry patterns in the structure of light nuclei, independent of whether the system Hamiltonian is phenomenological in nature or derived from realistic interactions. We show results of large-scale nuclear structure computations based on the ab initio symmetry-adapted no-core shell model that use only a fraction of the model space. In addition, the symmetry patterns unveiled in these results are employed to explore ultra-large model spaces for 12C. The outcome suggests a possible path forward for realizing collective theories that target correlated highly-deformed and alpha-cluster structures in terms of microscopic degrees of freedom that build forward from the nucleon-nucleon interaction itself.

Cluster structure in light nuclei studied with few-body models

We present our attempt at describing the low-lying states of A = 16 nuclei in a single scheme, a 12C core-plus-few-nucleon model. Promising results are obtained for 16C and 16O, which suggest the coexistence of single-particle and cluster structure.

Exotic cluster structure in light nuclei

We discuss the appearance of various cluster structures in light nuclei. One of the examples is the appearance of geometric cluster configurations; gas-like α cluster states found in 12C and 16O could be stabilized with geometric shapes by adding neutrons or giving large angular momentum. We show in 16O that four α particles can have linear configurations with large angular momentum, which is very stable with respect to the bending motion using Skyrme cranked Hartree-Fock method. There exists a region of angular momentum (13-18 ℏ) where the linear chain configuration is stabilized. The calculated moment of inertia (ℏ2/2(-_ ~ 0.06-0.08 MeV) agrees well with conventional cluster model calculations. Another example of exotic cluster structure is the gas-like state of α clusters. The most famous example is the second 0+ state in 12C, the so called Hoyle state, which plays a dominant role in the synthesis of 12C and the heavier elements in the stars. We go one step further that such a dilute state of α particles exists around a strongly bound core in heavier systems. This study is performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function, and first we apply such method to three α state around a 40Ca core. Furthermore, coupling effect to other low-lying cluster states is taken into account; a large isoscalar monopole (E0) transition strength from the ground to the gas-like state is discussed in 24Mg. The gas-like state of two α clusters in 24Mg around the 16O core appears slightly below the 2α-thresliold energy.

Skyrme-Hartree-Fock plus Tensor Correction for Nuclear Matter

We study the equation of states of symmetric and pure neutron matter in the SkyrmeHartree-Fock (SHF) model with tensor corrections. We are aware now that the pion exchange interaction has a significant contribution to nuclear structure in light nuclei. The pion generates a strong tensor interaction between two nucleons, which cannot be treated within the Hartree-Fock framework for the spin-saturated system such as homogeneous nuclear matter. Therefore, we study the role of the tensor interaction based on the SHF model, in which we extend it by explicitly introducing two-particle-two-hole (2p-2h) excitations for the treatment of the tensor interaction in symmetric nuclear matter and pure neutron matter. We are able to describe infinite matter very well using the SHF model with tensor corrections. We also discuss the connection between the symmetry energy and the tensor interaction in this framework. Subject Index: 201

Simplified Modeling of Cluster-Shell Competition and Appearance of Various Cluster Structures in Light Nuclei

Simplified Modeling of Cluster-Shell Competition and Appearance of Various Cluster Structures in Light Nuclei

Low-energy nuclear reactions with double-solenoid-based radioactive nuclear beam

The University of Notre Dame, USA (Becchetti et al, Nucl. Instrum. Methods Res.A505, 377 (2003) and later the University of Sao Paulo, Brazil (Lichtenthaler et al, Eur. Phys. J.A25, S-01, 733 (2005)) adopted a system based on superconducting solenoids to produce low-energy radioactive nuclear beams. In these systems the solenoids act as thick lenses to collect, select, and focus the secondary beam into a scattering chamber. Many experiments with radioactive light particle beams (RNB) such as 6He, 7Be, 8Li, 8B have been performed at these two facilities. These low-energy RNB have been used to investigate low-energy reactions such as elastic scattering, transfer and breakup, providing useful information on the structure of light nuclei near the drip line and on astrophysics. Total reaction cross-sections, derived from elastic scattering analysis, have also been investigated for light system as a function of energy and the role of breakup of weakly bound or exotic nuclei is discussed.

Description of nuclear structures in light nuclei with Brueckner-AMD

We develop the new antisymmetrized molecular dynamics (AMD) method, Brueckner-AMD, which makes us perform the AMD calculations starting from the realistic nuclear force. In the Brueckner-AMD, the single-particle orbits of AMD can be applied straightforward to the Bethe-Goldstone equation in the Brueck- ner theory by using the AMD+Hartree-Fock method, and the G-matrices are determined with the single-particle energies of AMD self-consistently. In that sense, in this framework, the G-matrix in AMD can be solved theo- retically without any corrections. We present the applicability of the Brueckner-AMD to describe not only the ground states but also the excited states for some light nuclei, especially the excited 0 + state in 12 C which is not solved suffi ciently by the present shell model approaches, starting from the realistic nuclear force.

STUDY OF LIGHT NUCLEI WITH BRUECKNER-AMD+GCM

To describe excited nuclear states, we developed the Brueckner-AMD combining the Brueckner theory with Antisymmetrized Molecular Dynamics (AMD), which has been recently proposed as a new framework to study nuclear structure of light nuclei based on the realistic nuclear force. In the present framework, we formulate a multi-configuration calculation with Generator Coordinate Method (GCM) in the Brueckner-AMD. An application is shown for the excited states with positive and negative parities in 4 He , and the successful results and reliability of the present framework are discussed.