The European Physical Journal A最新文献

Leakage neutron spectra from a natural Pb sample (with a thickness along the beam penetration direction of d = 100 or 200 mm) bombarded by white spectrum source neutrons were measured in the 0(^circ ) direction using the time-of-flight method. The experiment was conducted at the Radioactive Ion Beam Line of the Heavy Ion Research Facility at the Institute of Modern Physics, Chinese Academy of Sciences, in Lanzhou. White spectrum source neutrons were generated by irradiating a 5 mm thick tungsten target with 80.5 MeV/u (^{12})C ions. In addition, theoretical results for the leaked neutron spectrum of Pb were calculated using GEANT4 combined with the INCL, BIC, and BERT physics models, as well as the evaluated nuclear data libraries ENDF/B-VIII.0, JEFF(-)3.3, and JENDL(-)4.0. The results demonstrate that the GEANT4 calculations reliably describe neutron transport processes in Pb targets under white spectrum neutron irradiation, although further refinement of the models remains necessary to enhance calculation precision.

The channeling radiation spectrum for electrons in the sub-GeV to several GeV range exhibits a broad peak at photon energies reaching several tens of MeV. This property makes it suitable for inducing ((gamma ), n) photonuclear reactions in a subsequent target. For a given radiator thickness, the flux of channeling radiation can surpass that of bremsstrahlung by over an order of magnitude. This high flux is highly effective for studying photonuclear reactions within the giant dipole resonance region and for producing pulsed neutron beams. Detailed yield calculations for neutrons from targets of Au, Pb, U, Zn, and Si reveal a complex dependence on both the incident electron beam’s energy and its alignment with the crystal’s channeling planes.

The n_TOF facility at CERN has undergone a major upgrade after the installation of a new spallation target, designed to improve the performance of both neutron beamlines at the experimental areas 1 and 2 (EAR1 and EAR2) and the commissioning of a new experimental area (NEAR). Due to improved coupling of the spallation target with the EAR2 beamline, the upgrade resulted in a significantly increased neutron flux and improved neutron energy resolution. This paper presents the results of the commissioning phase that followed to characterise the EAR2 neutron beamline and validate the FLUKA Monte Carlo simulations of the facility. The main characteristics of the neutron beam, namely the neutron flux, spatial profile and energy resolution, are evaluated and compared to the previous target. The neutron flux presents a general increase of 20% below 1 eV, 40% between 1 eV and 100 keV and 50% between 100 keV and 10 MeV. The measured width of the beam profile was 3 cm full width at half maximum (FWHM) at the reference position for neutron capture measurements. The energy resolution with the new spallation target shows a significant improvement compared to the previous one. Moreover, FLUKA Monte Carlo simulations present a good agreement with the measured neutron flux and profile within uncertainties, and a remarkable reproduction of the energy resolution.

Nuclear masses of exotic nuclei are important for both nuclear physics and astrophysics. The deformed relativistic Hartree–Bogoliubov theory in continuum (DRHBc) is capable of providing proper descriptions for exotic nuclei by simultaneously including deformation, pairing correlation and continuum effects, and a mass table of even-Z nuclei with (8 leqslant Z leqslant 120) has been developed based on the DRHBc theory. This work employs a methodology to estimate the masses of odd nuclei using neighboring even nuclei’s masses and microscopic pairing gaps, and the performance of microscopic pairing gaps are validated by comparing with empirical ones. Combining the DRHBc masses of even-Z nuclei and the estimated masses of odd-Z nuclei, a pseudo DRHBc mass table is developed, with the root-mean-square (rms) deviation from available mass data (sigma =1.47) MeV. Then this mass table is employed in the r-process simulation; results show that the differences in the details of pairing gaps do not yield qualitative discrepancy in r-process abundances, while the deformation effects can influence the r-process path and thus affect the r-process abundance. In particular, the nuclear shape transitions can even lead to the discontinuity of the r-process path, suggesting that incorporating triaxiality or beyond-mean-field effects would be valuable for further improvement.

In many astrophysical scenarios, alpha induced reactions on noble gas nuclei play a crucial role. Studying these reactions in the laboratory requires the noble gas atoms to be confined in a sufficient amount to allow the reactions. At Atomki thin-windowed gas-cell targets were developed and improved for studying alpha induced reactions on noble gases. Several stages of the gas-cell design used for activation experiments and lately a version to be used for particle scattering experiments will be presented. A new experimental study of the ³He((alpha ),(gamma ))⁷Be reaction with one of the activation gas-cell targets was performed. This reaction plays an important role both in the solar pp-chains and in big bang nucleosynthesis. The reaction cross section was measured in the past in several works, however, there are still energy regions lacking experimental data, rendering the extrapolations towards the astrophysically relevant energies uncertain. New experimental total cross section of the ³He((alpha ),(gamma ))⁷Be reaction was thus determined here in the energy range of (E_mathrm {c.m.} = 2600-3000) keV in about 50 keV energy steps. These results confirm the overall trend, and also the absolute scale set by the only one previous measurement in this energy range. In addition, two pilot experiments with the scattering cell were performed aiming to study the ⁴He((alpha ),(alpha ))⁴He and ¹²⁴Xe((alpha ),(alpha ))¹²⁴Xe reactions at (E_alpha = 18) MeV. These studies benchmark the performance of the cell and detection system both for light and heavy noble gas targets.

Alpha decay is a dominant decay mode in heavy and superheavy nuclei, offering valuable insight into nuclear structure and stability, particularly in regions with sparse experimental data. In this work, we employ symbolic modeling using Kolmogorov–Arnold networks (KAN) to develop interpretable empirical formulas for predicting (alpha )-decay half-lives. A dataset of 373 ground-state (alpha )-emitters was used, with input features derived from both physical properties and prior feature importance analysis via XGBoost. The resulting symbolic expression demonstrates strong agreement with experimental data, achieving a root mean square error (RMSE) of 0.455 and mean absolute error (MAE) of 0.367, while retaining interpretability. Extrapolation tests on superheavy elements with (Z = 105)–120 further confirm the model’s consistency with existing empirical models, other machine learning models, and experimental values. The findings highlight the effectiveness of KAN in generating compact, accurate, and generalizable models for nuclear decay processes.

Why do quantum particles form a hierarchical structure: quarks, hadrons, nuclei, atoms, and molecules? This is a fundamental question, and its answer is still elusive. Each hierarchical layer is characterized by the constituent particles, which are composite particles except for the quark hierarchy. Such a building block is regarded as a cluster and plays a role in forming a hierarchy. In the boundary of the neighboring hierarchies, we may find intermediate hierarchies, called semi-hierarchies, where a range of characteristic clusters, such as hadronic molecules, exotic hadrons, neutron halos, (alpha ) clusters, and Feshbach molecules, appear. Such a cluster structure has some common features throughout the hierarchical layers with different scales. We discuss the role of clusters and their formation in semi-hierarchies.

This work introduces a novel approach to the nuclear deformation factor (R_{text {AA}},) grounded in the dynamical effects of the Quark-Gluon Plasma on parton momentum. The approach uses the Blast-Wave method combined with Tsallis Statistics, within the Cooper–Frye freeze-out framework and, by profiting from appropriate simplifications, it gives analytical expressions that describe the observed (R_{AA}) for two sets of independent measurements at (sqrt{s}=2.76) TeV and (sqrt{s}=5.02) TeV. A nonlinear dynamical equation describes the dynamics and leads to log-periodic oscillations. With the analytical solutions for that equation, it is possible to link the dynamical approach with the complex-q formalism, which was proposed to describe the log-oscillations observed in experimental data.

With the advancement of first-principles calculations for baryon–baryon interactions, it becomes possible to obtain reliable hyperon–nucleon potentials by lattice QCD simulations with the HAL QCD method. High-precision few-body methods, such as the Gaussian Expansion Method (GEM), are applicable to solve quantum few-body systems up to four- and five-body systems. By combining the HAL QCD potentials with the GEM, one can predict the level structure of novel hypernuclei prior to experimental observation. In this review, we utilize the lattice QCD (NXi ) potential obtained by the HAL QCD method to investigate the few-body systems (NNXi ) and (NNNXi ). Our analysis indicates that the lightest bound (Xi ) hypernucleus is the (NNNXi ) system. To extract detailed information on the isospin and spin components of the (NXi ) interaction, we perform a four-body calculation for the (alpha alpha NXi ) system with the total isospin (T = 0) and (T = 1). We demonstrate that the level structure of this system is sensitive to the isospin and spin dependencies of the (NXi ) interaction. Furthermore, we propose experimental investigations to produce the (NNNXi ) and (alpha alpha NXi ) systems via the ((K^-, K^+)) and ((K^-, K^0)) reactions on ⁴He and ¹⁰B targets, respectively.

The energy distributions and the absolute yields of the long-range alpha particles and the tritons emitted in the thermal neutron induced ternary fission of ²³⁵U were measured using a twin-gridded ionization chamber and a highly pure thermal neutron beam of the Xi’an pulsed reactor. The mean energy and FWHM of the long-range alpha particles are (15.8 ± 0.3) MeV and (9.5 ± 0.3) MeV, respectively. The mean energy and FWHM of the tritons are (8.4 ± 0.3) MeV and (6.9 ± 0.4) MeV, respectively. The absolute yields of the long-range alpha particles and the tritons are (1.74 ± 0.05) × 10⁻³ and (1.21 ± 0.07) × 10⁻⁴, respectively. These results are discussed and compared with the data from previous measurements.