The European Physical Journal A最新文献

The advances in understanding and producing heavy and super-heavy elements is the subject of this topical collection. The main covered subjects are: the description of the theory, developments of super-heavies and the determination of the Island of Stability as well as the role of these nuclei as part of the r-process scenario. The accurate determination of reaction processes are crucial to enable advances in the production of the heaviest elements. A short summary of the achievements at some of the facilities, their improved spectrometers and recent spectroscopy results complete this topical collection.

This review explores the current understanding of collective excitations and the dynamics of heavy quark propagation in the quark-gluon plasma (QGP) formed in relativistic heavy-ion collisions. We focus on three core aspects: the theoretical modelling of the QGP, including momentum anisotropy, medium-induced collisions, finite chemical potential, and non-ideal interactions; the collective behaviours within the plasma; and the interaction dynamics of heavy quarks as they traverse the medium. Along with the polarization energy loss mechanisms, we also review the possibility of energy gain due to thermal field fluctuations. Lastly, we discuss how these theoretical insights can be tested through experiments and outline possible directions for future research.

The rapid development of ab initio nuclear structure methods towards doubly open-shell nuclei, heavy nuclei and greater accuracy occurs at the price of evermore increased computational costs, especially RAM and CPU time. While most of the numerical simulations are carried out by expanding relevant operators and wave functions on the spherical harmonic oscillator basis, alternative one-body bases offering advantages in terms of computational efficiency have recently been investigated. In particular, the so-called natural basis used in combination with symmetry-conserving methods applicable to doubly closed-shell nuclei has proven beneficial in this respect. The present work examines the performance of the natural basis in the context of symmetry-breaking many-body calculations enabling the description of superfluid and deformed open-shell nuclei at polynomial cost with system’s size. First, it is demonstrated that the advantage observed for closed-shell nuclei carries over to open-shell ones. A detailed investigation of natural-orbital wave functions provides useful insight to support this finding and to explain the superiority of the natural basis over alternative ones. Second, it is shown that the use of natural orbitals combined with importance-truncation techniques leads to an even greater gain in terms of computational costs. The present results pave the way for the systematic use of natural-orbital bases in future implementations of non-perturbative many-body methods.

The temperature-dependent level density parameter has been computed using the Ignatyuk method. The Ignatyuk level density parameter has a low temperature sensitivity and it is also obtained as a constant function or independent temperature function for nuclei that have a zero shell correction factor. In the present study, to improve this method, the asymptotic level density parameter mentioned in the Ignatyuk method has been replaced by the modified Lestone level density parameter and the new model called the modified Ignatyuk method (MI). After that, the thermal properties of the nucleus have been described using the MI method. Similarly, by considering temperature-dependent pairing correlation, the nucleus thermodynamic properties have been determined using the Lipkin-Nogami (LN) microscopic model. However, this model produces singularity in the heat capacity diagram due to eliminating pairing effects at the critical temperature. This issue has been modified by substituting the gap parameter with the mean value gap parameter from the Ginzburg-Landau method. This modification is known as the generalized Lipkin-Nogami (GLN) model. Finally, the thermodynamic quantities have been computed using the mentioned models and their results compared with each other as well as the level density compared to the experimental results.

To achieve a unified description of the one-neutron halo nuclei (^{15})C and (^{19})C from structural properties to reaction dynamics, we combine the microscopic, self-consistent deformed relativistic Hartree–Bogoliubov theory in the continuum (DRHBc) with the Glauber model. For (^{15})C, the valence neutron orbital with dominant (2s_{1/2}) components supports the experimental ground-state spin-parity and halo formation. The halo nature of (^{19})C is attributed to a prolate state with the valence neutron orbital also dominated by (2s_{1/2}) components. The neutron densities for the halo states of (^{15})C and (^{19})C are significantly more dilute than those for (^{14,16,18})C. With the DRHBc calculated densities of the core nucleus and the wave functions of the valence neutron as inputs, the reaction cross sections (RCSs) of (^{14text {--}19})C bombarding a carbon target and the longitudinal momentum distributions of the core residues with one-neutron removal from (^{15,17,19})C are calculated by the Glauber model. The results not only demonstrate a significant increase of RCS from (^{14})C to (^{15})C but also accurately reproduce the measured RCS for the (^{19})C + (^{12})C reaction. Compared to the (^{16})C residue from the one-neutron removal of (^{17})C, the longitudinal momentum distributions for (^{14})C and (^{18})C residues from (^{15})C and (^{19})C, respectively, are notably narrower and exhibit clear peak shapes, supporting the halo structure of (^{15})C and (^{19})C. These findings further validate the DRHBc + Glauber approach, following its successful applications to the halo nuclei (^{31})Ne and (^{37})Mg.

The non-monotonic behavior of the speed of sound for isospin imbalanced strongly interacting matter, found by recent lattice QCD simulations, can be reproduced within the Nambu–Jona-Lasinio model and Linear Sigma Model with quarks when the couplings become isospin chemical potential-dependent. The introduction of medium-dependent couplings can potentially affect the equivalence between the thermodynamic relations and their definitions from statistical mechanics. We describe the procedure to compensate for the introduction of medium-dependent couplings to preserve the correct thermodynamic identities. We find the isospin chemical potential dependence for the couplings from the isospin density LQCD data and, after finding the compensating function to correctly describe the pressure, we show that the description of the square of the speed of sound reported by LQCD is well reproduced when using the found medium-dependent couplings in both models.

In this study, we have applied the Total Monte Carlo (TMC) methodology in the simulation of the de-excitation process of primary fission fragments (FF) within the TALYS code. Our objective was to develop a method for assessing fission model deficiencies and parameter sensitivities. The input fission fragment data used by TALYS were systematically varied. This was done using the GEF code to generate 10,000 random files by randomizing the 94 model parameters of GEF that influence both fission yields and their energy distributions. The GEF parameters were varied randomly within 3% of the default value, assuming a normal probability distribution. As a result of this parameter variation, significant changes could be identified for several observables, including the multiplicities of (gamma ) rays and prompt neutrons, as well as their spectra. Additionally, we investigate the impact of angular momentum distribution on the de-excitation data of both GEF and TALYS. Finally, we present an attempt to construct a best parameter file benchmarked against evaluated nuclear data files.

The present work presents a detailed analysis of angular distribution data for the ¹⁵N + ¹⁶O system in the energy range E_c.m. = 10.3–20.6 MeV that are characterized by pronounced increases in cross sections at large angles > 130°. These data sets allow for the energy dependence of elastic scattering potentials and elastic proton transfer to be explored from energies just below the Coulomb barrier to energies about 1.5 times its value. For this purpose, we have implemented various forms, both phenomenological and microscopic, for the interaction potentials. An elastic proton transfer amplitude for the ¹⁶O → p + ¹⁵N configuration was added to the scattering analysis through DWBA calculations. The extracted amplitudes were roughly energy and optical model form independent and yielded a good description of the enhanced large angle cross sections. These amplitudes when then converted to ¹⁶O → p + ¹⁵N spectroscopic factors (SF), are in good agreement with previously reported light ion reaction ones. Possible channel coupling effects on the large angle cross sections that included excitation of ¹⁶O and transfer to excited ¹⁵N states were carried out through Coupled Reaction Channels (CRC) calculations and found to be small.

Exact analytical solutions for the low-lying eigenfunctions and eigenvalues of the Bohr Hamiltonian using a sextic potential were presented recently in J. Phys. G: Nucl. Part. Phys. 48, 085102 (2021). Here, they are applied to describe even-even Xe and Ba isotopes with mass numbers from A = 124 to 134 and A = 126 to 136, respectively. The aim of this study is to investigate the possible transition in these isotopic chains from deformed (gamma )-independent to spherical shape phases. For this purpose, a detailed analysis of each isotope, including excitation energies and B(E2) transition rates, is presented. Special attention is paid to transitions from the first two excited (0^+) levels to the (2^+_1) and (2^+_2) levels, as these transitions assume different values for vibrating spherical and deformed nuclei, offering insights into possible shape phase transitions. The three parameters of the Hamiltonian have been determined using a weighted least squares fit procedure. This produces the corresponding energy surface for each isotope. This analysis shows that all studied isotopes are deformed, with moderate deformations, except for the heaviest studied isotope in each isotopic chain, which is calculated to be spherical. In addition to energy excitations and B(E2) transitions, other observables such as nuclear radii are also calculated.

The (^{246})Cm(n,(gamma )) and (^{248})Cm(n,(gamma )) cross-sections have been measured at the Experimental Area 2 (EAR2) of the n_TOF facility at CERN with three C(_6)D(_6) detectors. This measurement is part of a collective effort to improve the capture cross-section data for Minor Actinides (MAs), which are required to estimate the production and transmutation rates of these isotopes in light water reactors and innovative reactor systems. In particular, the neutron capture in (^{246})Cm and (^{248})Cm open the path for the formation of other Cm isotopes and heavier elements such as Bk and Cf and the knowledge of (n,(gamma )) cross-sections of these Cm isotopes plays an important role in the transport, transmutation and storage of the spent nuclear fuel. The reactions (^{246})Cm(n,(gamma )) and (^{248})Cm(n,(gamma )) have been the two first capture measurements analyzed at n_TOF EAR2. Until this experiment and two recent measurements performed at J-PARC, there was only one set of data of the capture cross-sections of (^{246})Cm and (^{248})Cm, that was obtained in 1969 in an underground nuclear explosion experiment. In the measurement at n_TOF a total of 13 resonances of (^{246})Cm between 4 and 400 eV and 5 of (^{248})Cm between 7 and 100 eV have been identified and fitted. The radiative kernels obtained for (^{246})Cm are compatible with JENDL-5, but some of them are not with JENDL-4, which has been adopted by JEFF-3.3 and ENDF/B-VIII.0. The radiative kernels obtained for the first three (^{248})Cm resonances are compatible with JENDL-5, however, the other two are not compatible with any other evaluation and are 20 and 60% larger than JENDL-5.