Dissipation retards fission, resulting in a drop in the first-chance fission probability of a fissioning nucleus with respect to its statistical model value. We use the Langevin model to compute the evolution of the drop (due to friction), Pf0drop, for the fissioning systems ²²⁰Th and ²⁴⁰Cf with the presaddle friction strength (β). The first-chance fission probability is shown to depend sensitively on β, and the sensitivity is apparently greater than that of the total fission probability. We further find that although the total fission probability of heavy ²⁴⁰Cf is insensitive to β, its first-chance fission probability is quite sensitive to β. These results suggest that, to strongly limit the presaddle friction strength, an optimal experimental avenue is to measure the first-chance fission probability of heavy fissioning nuclei.

The Rare isotope Accelerator complex for ON-line experiments (RAON) is a new radioactive ion beam accelerator facility under construction in Korea. The large acceptance multi-purpose spectrometer (LAMPS) is one of the experimental devices for nuclear physics at RAON. It focuses on the nuclear symmetry energy at supra-saturation densities. The LAMPS Collaboration has developed and constructed various detector elements, including a time projection chamber (TPC) and a forward neutron detector array (NDA). From the positron beam test, the drift velocity of the secondary electrons in the TPC is 5.3 ± 0.2 cm/μs with P10 gas mixture, and the position resolution for pads with dimensions of 4 × 15 mm² is in the range of ∼0.6–0.8 mm, depending on the beam position. From the neutron beam test, the energy resolution of the prototype neutron detector module is determined to be 3.4%, and the position resolution is estimated to be better than 5.28 cm. At present, the construction of the LAMPS neutron detector system is in progress.

Synthesis of superheavy elements beyond oganesson is facing new challenges as new target-projectile combinations are necessary. Guidance from models is thus expected for future experiments. However, hindered fusion models are not well established and predictions in the fission barriers span few MeVs. Consequently, predictions are not reliable. Strategies to constrain both fusion hindrance and fission barriers are necessary to improve the predictive power of the models. But, there is no hope to get an accuracy better than one order of magnitude in fusion-evaporation reactions leading to superheavy elements synthesis.

The effects of the in-medium nucleon-nucleon (NN) elastic cross section on the observables in heavy ion collisions in the Fermi energy domain are investigated within the framework of the ultrarelativistic quantum molecular dynamics model. The results simulated using medium correction factors of F=σNNin−medium/σNNfree=0.2, 0.3, 0.5 and the density- and momentum-dependent factor obtained from the FU3FP1 parametrization are compared with the FOPI and INDRA experimental data. It is found that the calculations using the correction factors F = 0.2 and 0.5 reproduce the experimental data (i.e., collective flow and nuclear stopping) at 40 and 150 MeV/nucleon, respectively. Calculations with the FU3FP1 parametrization can best fit these experimental data. These conclusions can be confirmed in both ¹⁹⁷Au+¹⁹⁷Au and ¹²⁹Xe+¹²⁰Sn.

Extracting the equation of state (EOS) and symmetry energy of dense neutron-rich matter from astrophysical observations is a longstanding goal of nuclear astrophysics. To facilitate the realization of this goal, the feasibility of using an explicitly isospin-dependent parametric EOS for neutron star matter was investigated recently in [1-3]. In this contribution, in addition to outlining the model framework and summarizing the most important findings from [1-3], we report a few new results regarding constraining parameters characterizing the high-density behavior of nuclear symmetry energy. In particular, the constraints on the pressure of neutron star matter extracted from combining the X-ray observations of the neutron star radius, the minimum maximum mass M=2.01 M_⊙, and causality condition agree very well with those extracted from analyzing the tidal deformability data by the LIGO+Virgo Collaborations. The limitations of using the radius and/or tidal deformability of neutron stars to constrain the high-density nuclear symmetry energy are discussed.

Quark interactions with topological gluon fields in quantum chromodynamics can yield local 𝒫 and 𝒞𝒫 violations that could explain the matter–antimatter asymmetry in our universe. Effects of 𝒫 and 𝒞𝒫 violations can lead to charge separation under a strong magnetic field, a phenomenon called the chiral magnetic effect (CME). Early measurements of the CME-induced charge separation in heavy ion collisions are dominated by physics backgrounds. This report discusses the recent innovative efforts in eliminating those backgrounds, namely, by event-shape engineering, invariant-mass dependence, and reaction and participant plane comparison. The background-free CME measurements using these novel methods are presented.

Light and heavy clusters are calculated for warm stellar matter in the framework of relativistic mean-field models, in the single-nucleus approximation. The clusters abundances are determined from the minimization of the free energy. In-medium effects of light cluster properties are included by introducing an explicit binding energy shift analytically calculated in the Thomas-Fermi approximation, and the coupling constants are fixed by imposing that the virial limit at low density is recovered. The resulting light cluster abundances come out to be in reasonable agreement with constraints at higher density coming from heavy ion collision data. Some comparisons with microscopic calculations are also shown.

Finite Element Analysis (FEA) method was employed to perform three-dimensional (3D) electric field simulations for gas detectors with multiple wire electrodes. A new element refinement method developed for use in conjunction with the FEA program ANSYS allows successful meshing of the wires without physically inputting the wires in the chamber geometry. First, we demonstrate a model with only one wire, for which we calculate the potential distributions on the central plane and the end-cap region. The results are compared to the calculations obtained using GARFIELD, a two-dimensional program that uses the nearly exact boundary element method (NEBEM). Then we extend the method to same model, but with seven wires. Our results suggest that the new method can be applied easily to the 3D electric field calculations for complicated gas detectors with many wires and complicated geometry such as multiwire proportional chambers (MWPC) and time projection chambers (TPC).

The nuclear mean-field potential built up during the ¹²C+¹²C and ¹⁶O+¹⁶O collisions at low energies relevant for the carbon- and oxygen-burning processes is constructed within the double-folding model (DFM) using the realistic ground-state densities of ¹²C and ¹⁶O, and CDM3Yn density-dependent nucleon-nucleon (NN) interaction. The rearrangement term, indicated by the Hugenholtz–van Hove theorem for the single-particle energy in nuclear matter, is properly considered in the DFM calculation. To validate the use of the density-dependent NN interaction at low energies, an adiabatic approximation was suggested for the dinuclear overlap density. The reliability of the nucleus-nucleus potential predicted through this low-energy version of the DFM was tested in the optical model (OM) analysis of the elastic ¹²C+¹²C and ¹⁶O+¹⁶O scattering data at energies below 10 MeV/nucleon. These OM results provide a consistently good description of the elastic angular distributions and 90° excitation function. The dinuclear mean-field potential predicted by the DFM is further used to determine the astrophysical S factor of the ¹²C+¹²C and ¹⁶O+¹⁶O fusions in the barrier penetration model. Without any adjustment of the potential strength, our results reproduce the non-resonant behavior of the S factor of the ¹²C+¹²C and ¹⁶O+¹⁶O fusions very well over a wide range of energies.

Clustering is a general phenomenon observed in light nuclei, especially in neutron-rich nuclei in which molecular configurations can be formed with various combinations of valence neutrons. Thus far, many theoretical models have been developed to describe nuclear clustering phenomena. These models are outlined in this review article, with an emphasis on their basic formulations and physical ingredients. In addition, various experimental tools, such as inelastic excitation and decay, transfer reactions, and resonant scattering reactions, have been applied to investigate the cluster structures inside the nucleus. Each tool possesses certain advantages and favorable applications, which are also described. In the case of neutron-rich nuclei, cluster structures may be configured as molecular states that form rotational bands with an extremely large moment of inertia and generate relatively large cluster decay width. The major experimental criteria for the identification of cluster formation are discussed herein.

The mechanism of multinucleon transfer reactions has been investigated within the dinuclear system model, in which the sequential nucleon transfer is described by solving a set of microscopically derived master equations. The transfer dynamics in the reaction of ¹³⁶Xe+²⁰⁸Pb near Coulomb barrier energies is thoroughly analyzed. It is found that the total kinetic energies of primary fragments are dissipated from the relative motion energy of two touching nuclei and exhibit a symmetric distribution along the fragment mass. The angular distribution of the projectile-like fragments moves forward with increasing beam energy. However, the target-like fragments exhibit an opposite trend. The shell effect is pronounced due to the fragment yields in multinucleon transfer reactions.

In recent years, the collective motion properties of global rotation of the symmetric colliding system in relativistic energies have been investigated. In addition, the initial geometrical shape effects on the collective flows have been explored using a hydrodynamical model, a transport model etc. In this work, we study the asymmetric ¹²C + ¹⁹⁷Au collision at 200 GeV/c and the effect of the exotic nuclear structure on the global rotation using a multi-phase transport model. The global angular momentum and averaged angular speed were calculated and discussed for the collision system at different evolution stages.

TMSR uses nuclear graphite as a neutron moderator, a reflector, and the structural material, and utilizes molten salt as a coolant. When running normally, the graphite components are immersed in the molten salt. Thus, the nuclear graphite comes into direct contact with the molten salt, which infiltrate the open pores of the nuclear graphite. This infiltration may influence the stress analysis of the graphite component. In this study, a User MATerial (UMAT) subroutine was used to analyze the stress distribution of the graphite component, both with and without molten salt infiltration. Many influence factors were taken into consideration, such as the dose gradient, the shape of the permeation zone, and the permeation area. The results show that the dose gradient, shape, and area of the permeation zone all significantly influence the stress distribution. Furthermore, the results of the stress analysis indicate that for a regular graphite component with a square cross-section, the peak maximum principal stress value occurs at the center of the cross-section, and the symmetry of the maximum principal stress distributions was modified by quarter circle and half ellipse permeation zones.

This paper presents the determination of the fuel burnup distribution of the Dalat nuclear research reactor (DNRR) using a method of measurements at subcritical conditions. The method is based on the assumption of linear dependence of the reactivity on the burnup of fuel bundles and the measurements at subcritical conditions. The measurements were conducted for seven selected fuel bundles in two different measuring sequences. The measured burnup values have also been compared with the calculations for verifying the method and the measurement procedure. The results obtained with the three detectors have a good agreement with each other with a discrepancy less than 1.0%. The errors of the measured burnup values are within 6%. Comparison between the calculated and measured burnup values shows that the discrepancy of the C/E ratio is within 9% compared to unity. The results indicate that the method of measurements at subcritical conditions could be well applied to determine the relative burnup distribution of the DNRR.

Herein, a feasible method is proposed to compensate the high-order effect during bunch length compression; thereby, enhancing the peak current of a high repetition rate X-ray free-electron laser source. In the proposed method, the corrugated structure is inserted downstream of the high-order harmonic cavities to function as a passive linearizer and enhance the longitudinal profile of the electron beam. Three-dimensional simulations are performed to analyze the evolution of the longitudinal phase space and the results demonstrate that the profile of the electron beam is improved and the peak current can be easily optimized to over 2 kA with a bunch charge of 100 pC.

The betatron tune is an important parameter in a storage ring to enable stable operation. A tune adjustment tool with a small impact on the beam dynamics is useful for user operation and machine studies. Therefore, a tune knob is developed for the Hefei Light Source-II (HLS-II) storage ring. Owing to the compactness of the storage ring, a global adjustment mechanism is adopted. To reduce the impact on beam injection, only quadrupole families outside the injection section are used by the tune knob, and the β functions of the injection section remain unchanged. A code is developed based on the accelerator simulation software, MAD-X, to calculate the adjustment of the quadrupole strengths. The Accelerator Toolbox is used to double check the accuracy of the tune knob. Online measurement of the tune knob is also performed. The result shows that the tune knob works well when the tune is adjusted in a specific range. Betatron coupling measurement is also carried out, showing an application of the tune knob on machine studies. In this paper, the development of the tune knob and its experimental results in the HLS-II storage ring are reported in detail.

We propose the construction of a compact linac as the injector of a cancer therapy facility at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS). Based on a traditional setup, a new compact fast-bunching design is first introduced to optimize the 600 keV/u RFQ with a 0.05 pmA ¹²C⁴⁺ beam. This shortens the RFQ structure length from the standard design value of 272–230 cm, while effectively regulating the particle loss and emittance growth. In addition, a detailed error analysis was performed after the optimization process. The error sources cover input beam parameters errors, machining errors and alignment errors. The simulation results show that the beam loss and emittance growth of the RFQ are acceptable and within typical ranges of error.