The properties of neutrons from spectator sources produced in Sn-107,Sn-124 + Sn-120 collisions at 600 MeV/nucleon are studied. The isospin-dependent quantum molecular dynamics (IQMD) model is used to describe the dynamical process of fragmentation, and the statistical model GEMINI is applied to simulate the secondary decay of the pre-fragments. The differential cross section and multiplicity of the neutrons emitted from the spectator source are used to prove the model's feasibility. The temperatures of the spectator source are extracted by two-source-fitting the transverse momentum distributions of the neutrons using the classical Maxwellian functions. The temperatures of the spectator sources extracted from calculations are consistent with the experimental data, those from the SMM model, and the isotopic temperature . However, the participant source exhibits anomalously high temperatures. Our work suggests the possible model-errors of the IQMD+GEMINI model when describing the neutron emission from the participant source, which is reference for the further development of the model.

We investigate the sensitivity of calcium production to nuclear reaction rates of a 40 solar-mass Population III star using 1D multi-zone stellar models. A comprehensive nuclear reaction network was constructed, and all (p,γ) and (p,α) reaction rates were individually varied by a factor of 10 up and down, identifying 13 preliminary key reactions for calcium production. To propagate the reaction rate uncertainties on calcium production, two sets of Monte Carlo simulations were performed for these key reactions: one adopting STARLIB reaction rates and the other incorporating updated rates from recent experimental data and evaluations. Our results show that Monte Carlo simulations using the updated rates show good agreement with the observed calcium abundance of the extremely iron-poor star SMSS J031300.36-670839.3 within the 68 Additionally, comparisons between 20 solar-mass and 40 solar-mass Population III stellar models confirm that the latter, with updated reaction rates, is more capable of reproducing the observed Ca abundance and [Ca/Mg] ratio.

The Jiangmen Underground Neutrino Observatory (JUNO) collaboration has completed the construction of the 20,000-ton liquid scintillator detector and the associated muon veto detector system. To meet the physics objectives, the materials used in the detector must exhibit low radioactive contamination. The single-event rate in the fiducial volume (R < 17.2 m) of the scintillator is required to be approximately 7 Hz for energies above 0.7 MeV, resulting in an accidental coincidence background of about 1 event per day for reactor neutrino physics analyses. Since the beginning of the construction phase, we have screened the natural radioactivity content of thousands of materials, to select those that meet the design background budget. The radioactive impurity concentrations of the materials ultimately used in the JUNO detector are summarized in this paper. The construction of the entire detector and the subsequent filling of the liquid scintillator were completed in August 2025. From the initial data, the total count rate of natural radioactivity within the detector's fiducial volume has met the requirements and is sufficient to support the reactor antineutrino analysis.

This study establishes neutronics models of both single-beam and double-beam driven ADS subcritical reactors based on the CiADS core geometry using the OpenMC code, systematically comparing their performance in terms of power distribution, neutron flux, transmutation of long-lived fission products (LLFPs), and breeding of plutonium. Comparison shows that the discrepancy in the effective neutron multiplication factor between the model and reference results is within ±0.003, and the neutron energy spectra agree well in the range of 10−4MeV to 10 MeV. The results indicate that the double-beam design significantly improves the axial power distribution uniformity, with the full width at half maximum increasing from 58.8 cm in the single-beam system to 60.5 cm in the double-beam system, along with a general increase in neutron flux within fuel assemblies. Regarding transmutation performance, the double-beam system enhances the transmutation rate of 135Cs in LLFP assemblies by 58% and significantly promotes the breeding of 239Pu. These findings demonstrate that the double-beam design offers clear advantages in improving power flattening, enhancing transmutation efficiency, and promoting actinide conversion in ADS systems, providing neutronic insights for future engineering conceptual design of multi-beam ADS configurations.

One-neutron removal reactions exhibit a strong proton–neutron asymmetry dependence in the inclusive reduction factor Rs, a long-standing issue that has been discussed in terms of both possible intrinsic isospin dependence of single-particle strength and reaction-mechanism effects. We address this issue by reframing inclusive removal as a coupled fast-dynamics and deexcitation process, and by testing this transport–deexcitation description against a global data set of cross sections and momentum distributions. Confronting 73 one-neutron removal cross sections and 28 residue parallel-momentum distributions with isospin-dependent quantum molecular dynamics followed by GEMINI evaporation indicates, within the present transport–deexcitation framework, that the apparent Rs–ΔS trend is correlated with evaporation feeding and evaporation loss. Using the estimated feeding and loss corrections, we construct a purified reduction factor Rdir that is intended to be closer than the inclusive Rs to the reduction factor conventionally associated with single-particle strength. The resulting Rdir exhibits a much weaker ΔS dependence within current uncertainties, consistent with the weak isospin-asymmetry dependence observed in nucleon-transfer and quasifree-knockout systematics.

Type I X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars, involving hundreds of nuclei and thousands of reactions with larger uncertainties in reaction rates. To investigate the impact of nuclear reaction rate uncertainties on type I X-ray burst nucleosynthesis, comprehensive Monte Carlo simulations were performed with temperature-independent and -dependent variations in reaction rates using the REACLIB and STARLIB libraries, respectively. A total of 1711 (p, gamma), (p, alpha), (alpha, p), and (alpha, gamma) reaction rates are varied simultaneously along with their inverse reactions via detailed balance. For the first time, it has been found that Monte Carlo sampling with larger perturbations to these reaction rates may lead to multipeak abundance distributions for certain isotopes, such as 64Zn and 55Co. These multipeak structures arise not only from coupled reactions but also from single reactions in some cases. Our studies also confirm previously identified key reactions and provide more robust lists that deserve priority consideration in future studies.

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kton liquid scintillator-based, low-radioactivity, multi-purpose neutrino detector located 693 meters (1800 m.w.e.) underground in the Guangdong province, China. To detect scintillation light produced in the target, the detector is equipped with 17,612 20-inch photomultipliers (PMTs), forming the Large PMT system (LPMT). In addition, 25,600 3-inch photomultipliers (the Small Photomultiplier System or SPMT) are deployed in the gaps between the LPMTs. This paper presents the design and performance of the underwater front-end electronics developed for the SPMT system. It details the individual electronics boards and their key components, the inter-board interfaces, the system-level design, and the firmware architecture that supports data acquisition and control. It also outlines mechanical and thermal integration, board validation procedures, and system performance metrics. The readout chain includes digitization of 128 PMT channels per unit, synchronized time-stamping, charge measurement, event packaging, and bandwidth management. Comprehensive validation confirms the system's readiness to meet JUNO's stringent physics goals. The underwater electronics achieve noise levels as low as 0.04 photoelectrons with minimal crosstalk (below 0.4

Abstract The orientation dependence of the near-Coulomb-barrier reaction ⁶⁴Ni + ²³⁸U at a center-of-mass energy of 301.05 MeV is investigated within the Boltzmann–Uehling–Uhlenbeck transport framework. Three representative orientations of the deformed ²³⁸U target are considered, and an event-by-event window analysis is performed to connect final-state observables with the underlying contact-stage dynamics. The calculated fragment mass distribution, mass–angle distribution, and mass--total-kinetic-energy correlation reproduce the main qualitative features of the available experimental data, including the double-humped mass structure and the weak population near mass symmetry. Within the present event-identification criterion and evolution time, no fusion events are identified. The x orientation gives the largest quasifission component and the strongest mass drift toward symmetry, the z orientation is intermediate, whereas the y orientation is dominated by quasielastic or weakly dissipative events. The analysis of the contact probability P_cont(b), contact time T_cont, and fragment proton number Z, neutron number N, and N/Z ratio indicates that the orientation dependence originates from the combined effects of contact formation, contact lifetime, and nucleon-exchange efficiency through the neck region. These results provide a dynamical interpretation of how the entrance-channel orientation governs the branching between quasielastic and quasifission trajectories.

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kiloton liquid scintillator neutrino detector, located 650 meters (1800 m.w.e.) underground in Jiangmen, Guangdong, China. JUNO is primarily designed for reactor neutrino measurements and has been taking data since 2025. With the largest mass of its kind and an excellent energy resolution, JUNO is a leading observatory for high-precision measurements of MeV neutrinos. The standard global trigger system serves as the primary trigger for JUNO. We present a newly developed multi-messenger trigger system that extends the capabilities of the global trigger by providing a lower energy threshold and an independent monitoring capability. During the 2025 operation, it achieved an effective energy threshold of approximately 110 +/- 10 keV, providing a lower threshold configuration suitable for low-energy event analysis. The system shows the potential to further reduce the threshold to well below 100 keV. Based on the multi-messenger trigger system, an astrophysical monitor has been developed to receive and process external alerts from other messengers, such as gravitational-wave observations. A Transient Neutrino Burst Monitor is integrated to detect short-time-scale neutrino burst events and enables real-time monitoring of transient astrophysical phenomena. The system is sensitive to neutrino bursts from core-collapse supernovae within a distance of about 250 kpc.

20Na is a well-known β-delayed α emitter, owing to the large decay energy of 20Na above the α + 16O threshold in the A=5α daughter nucleus 20Ne. In this work, the decay property of 20Na is investigated in detail via the β-γ β-α and β-γ-α coincidence spectroscopy. As the day-one experiment of the Beijing Rare Isotope Facility (BRIF), the intense 20Na beam was produced using the Isotope Separator On Line (ISOL) technique through the 100 MeV proton bombarding a stack of MgO as a thick target. Specific interest was focused on the exotic decay mode of 20Na; the previously reported low-energy α lines at 713 and 846 keV were confirmed, and several weak β-γ-α decay sequences were clearly identified for the first time, thanks to the strong resolving power of α-γ coincidence spectroscopy. The decay properties of 20Na are compared to the shell model calculation, which agree reasonably well with the allowed β transition strengths and subsequent electro-magnetic transitions with the use of the sd shell-model space with the USDB interaction.

Understanding how fragment shell effects influence spontaneous fission mass yields remains a central challenge in nuclear fission theory. This work investigates the role of shell effects in the spontaneous fission of ^240Pu, ^232Th, and ^264Fm by combining microscopic collective dynamics with fragment-level shell analysis. A two-step framework is employed: first, the tunneling from the inner to outer turning points is described using the Wentzel-Kramers-Brillouin approximation along the least-action path on a potential energy surface calculated from constrained Hartree-Fock-Bogoliubov theory. Second, the dissipative descent from the outer turning points to scission is simulated via Langevin dynamics in a large collective space of quadrupole and octupole deformations. Fragment shell effects are quantified using smoothed level density indicators for representative even-even fragment pairs extracted from Langevin scission configurations. The analysis reveals that enhanced yields arise from a coherent overlap among dynamically populated scission configurations, low-energy regions on the fragment potential energy surfaces, and low neutron and/or proton level densities near the Fermi surface. Proton shell effects provide persistent microscopic selectivity in both light and heavy fragments across asymmetric channels, while neutron shell effects offer additional stabilization. Deformed shell effects at finite quadrupole and octupole deformations play a crucial role in stabilizing asymmetric fission channels. This work demonstrates that fission fragment yields reflect shell-favored configurations that are made accessible by the potential energy surface topology and populated by stochastic dynamics, with the largest yields corresponding to configurations where shell gaps provide maximal binding.

A liquid-nitrogen-cooled cryogenic gas target system has been developed and installed for radioactive ion beam (RIB) production at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Light-element gases (H_2, D_2, and ^4He) filled in the target cell were cooled to cryogenic temperatures, with the gas-cell outlet temperature typically monitored at 82–86 K during beam irradiation and operating pressures up to 1000 mbar. The system was used to produce ^7Be, ^16N, and ^15O RIBs via the ^1H(^7Li, ^7Be)n, ^2H(^15N, ^16N)p, and ^1H(^15N, ^15O)n inverse kinematics reactions, yielding purities of 85%, 99%, and 95%, with intensities of 1.02×10^6, 2.7×10^5, and 1.0×10^5 pps, respectively. A ^93mMo isomer beam was also produced via the ^4He(^94Zr, 5n)^93mMo reaction, achieving an intensity of 5.38×10^3 pps and a purity of 20% (which can be further improved to ∼50% with offline time-of-flight gating). By delivering a broader range of high-intensity secondary RIBs, this setup establishes a robust platform at RIBLL for low- and medium-energy nuclear astrophysics and reaction studies.

Over 25,600 3-inch photomultiplier tubes (PMTs) have been instrumented for the central detector of the Jiangmen Underground Neutrino Observatory. Each PMT is equipped with a high-voltage divider and a frontend cable with waterproof sealing. Groups of sixteen PMTs are connected to the underwater frontend readout electronics via specialized multi-channel waterproof connectors. This paper outlines the design and mass production processes for the high-voltage divider, the cable and connector, as well as the waterproof potting of the PMT bases. The results of the acceptance tests of all the integrated PMTs are also presented.

We found that a heavy target such as Pb is most suitable for determining the proton distribution radii of unstable nuclei through charge-changing cross-section (σ_cc) measurements. As a heavy ion probe, low-Z targets are routinely used to determine nucleon distribution radii of unstable isotopes. This approach has recently been extended to study proton distribution radii from σ_cc measurements. However, empirical scaling factors have to be introduced to apply the Glauber models. In the present work, we systematically investigated the scaling factor using 39 new σ_cc data of 18 p-shell nuclei on hydrogen, carbon, silver, and lead targets at around 240 MeV/nucleon. Together with the existing data, we reveal a universal dependence of the scaling factor on both the masses of target nuclei and the separation energies of projectile nuclei. The scaling factors decrease with increasing target-nucleus mass and converge to 1 for the highest-Z target, making the scaling unnecessary. We conclude that instead of a low-Z target, employing a heavy target such as Pb in σ_cc measurements is the best option to determine the proton distribution radii of unstable nuclei.

Accurate spallation-neutron source terms are essential for accelerator-driven systems (ADS), yet double-differential cross-section (DDX) data remain sparse, particularly for proton- ^nat Pb, a benchmark ADS target. We present a data-driven pathway from sparse measurements to dense DDX using a Bayesian tensor model together with a physics-consistent interpolation scheme tailored for ADS source-term construction. A total of 1,727 DDX points for proton– ^nat Pb, compiled from EXFOR and the literature, spanning eight incident energies (10 MeV–3 GeV) and seven angles (7.5– 150^∘ ), are used jointly to fit the tensor model. Under the selected hyperparameters, the model shows strong in-sample agreement on a logarithmic scale. For data-sparse checks, we compare predictions with the Bertini intranuclear-cascade model in Geant4 (and BERT_HP where available) on common discrete grids: Agreement is close below 10 MeV; in the 20–100 MeV band, where BERT/BERT_HP often underpredict the measurements, our predictions remain physically plausible. To deliver application-ready inputs, we construct a high-resolution dataset via bilinear interpolation in (E_p,θ ) on self-similar energy slices κ =ln (E_n/E_p) , evaluated on a regular grid with 1 MeV spacing in E_p and 0.5^∘ in θ , with a no-extrapolation policy. The interpolants preserve evaporation-like low-energy behavior and forward-peaked high-energy emission while remaining consistent with Geant4 trends. The resulting proton- ^nat Pb DDX dataset, covering the CiADS design point (500 MeV) and its neighborhood, can be coupled to transport codes (e.g., OpenMC) for anisotropic source-term calculations and can be extended to other targets and reactions.

Elemental fragmentation cross sections (EFCSs) of the N = Z nuclei Ar-36, Cl-34, S-32, P-30, and Si-28 on a carbon target were measured at approximately 300 MeV/nucleon using the RIBLL2 fragment separator at HIRFL. Among these, the cross sections for Cl-34 and P-30 are reported here for the first time, providing new data and extending EFCS measurements along the N = Z chain. The measured cross sections exhibit significant odd-even staggering as a function of the charge change Delta Z. The experimental results are compared with several empirical parametrizations, including Cummings, EPAX3, and FRACS, as well as with the isospin-dependent quantum molecular dynamics model (IQMD) coupled to the statistical decay code GEMINI. The IQMD+GEMINI calculations reproduce the experimental cross sections with an accuracy of approximately 7% and reasonably reproduce the observed odd-even staggering. Consistent with previous studies, comparisons of model predictions at different reaction stages demonstrate that the odd-even staggering in EFCSs predominantly originates from the de-excitation of excited primary fragments. These results further establish the robustness of this interpretation by extending its validity to the N = Z region.

Matter radii and charge radii are fundamental quantities that describe the size of atomic nuclei. Matter radii of unstable nuclei have been deduced from the precision interaction cross section measurements since the 1980s using the Glauber-type model. The sudden increase in radii paves the way for discovering exotic phenomena, such as halos and shell evolution. Similarly, measurements of charge-changing cross section (CCCS) have been proposed to extract the charge radii of unstable nuclei. This cross section represents the probability of removing at least one proton from projectile nuclei after collisions with reaction target nuclei. It is related to the proton density distribution of the projectile nuclei. Unlike the electron scattering and isotope shift methods, which are based on the well-known electromagnetic interaction, the cross section measurements combined with the Glauber model rely on the strong interaction. A reliable determination of charge radii crucially depends on decoupling the nuclear structure information from the reactions. Currently, only the direct interactions between protons in the projectile nuclei with protons and neutrons in the target nuclei have been considered in computing the charge-changing cross section in the framework of the Glauber model while treating the projectile's neutrons as spectators, i.e., it only includes the process of directly removing protons from the projectile nuclei. Recent studies of CCCSs for p-shell nuclei on C targets at about 900 and 300 MeV/nucleon show that such a model can reproduce the experimental data only by about 90%. This discrepancy from experiments by about 10% indicates the essential role of the projectile's neutrons in the charge-changing reactions. The charged particle evaporation (CPE) has been proposed to resolve this discrepancy. In this process, only neutrons are removed directly from projectile nuclei in the collision, and the residual as a hot pre-fragment, will then de-excite by emitting charged particles such as protons and alphas. The CPE contribution to the CCCS was found to be isospin-dependent. The charged particle evaporation can contribute to the experimental cross section by about 10% for the C target, while it can be enhanced by up to 50% for the hydrogen target. The evaporation effect reaches its maximum at nuclei with similar numbers of protons and neutrons. The latest study shows that a new phenomenological factor (S-1) can characterize this CPE well for each reaction target. This factor can be written explicitly as a linear function of the nucleon separation energies of the studied projectile nuclei, which allows one to consistently deduce the point-proton distribution radii from the cross sections on various targets. Experimentally, it remains challenging to distinguish between direct proton-removal and proton evaporation following neutron-removal processes in charge-changing reactions. The simplest mechanisms are the direct proton removals and the proton evaporation after neutron removals. It will be very important to determine and understand the mechanism behind the S 1-factor if one can distinguish the different sources of proton yields. For this purpose, we have employed the isospinindependent quantum molecular dynamics (IQMD) plus GEMINI model to simulate the heavy ion collisions at around 300 A AMeV for Si isotopes on carbon. Such simulations allow us to analyze and trace the outgoing protons. We show that it is possible to classify the produced protons by their angular distributions. New experiments are planned at the RIBLL2 beamline.

Background: Experiment of ^180Hg fission revealed a possible “new asymmetric fission mode” in the preactinide region, posing challenges to current fission theory. Similarity on shell effects are observed between fission and quasifission, providing possibility for widely exploring the topography of fission potential-energy surface (PES). Purpose: We aim to investigate the shell effects in the quasifission forming ^180Hg and to explore their connection with the ^180Hg fission. Method: ^68Zn+^112Sn, ^74Se+^106Pd, and ^80Kr+^100Ru central collisions at different energies and projectile orientations are calculated using the Skyrme time-dependent Hartree-Fock approach. The static fission properties are calculated with the constrained Hartree-Fock-Bogoliubov method and compared with the quasifission results. Results: Shell effects are found to hinder mass equilibration between the prefragments, enhancing the production of fragments near the 80/100 mass split. By comparing the quasifission trajectories with the PES in the (Q_20, Q_30) space, the role of PES ridge in forming fragments is identified. The presence of asymmetric valley causes the ^68Zn + ^112Sn quasifission exhibits prefragment mass equilibration process and scission-point configuration similar to those of fission. The elongated light fragment is found to be a key factor in reproducing the experimental fission total kinetic energies. Conclusions: By using quasifission dynamics as a probe of the fission pathway, the present calculations help clarify the specific influence of the PES topography. This highlights the importance of dynamical calculations for preactinide fission, where the manifestation of shell effects is not intuitively evident from the PES.

Accurately describing the quantum many-body dynamics during nuclear reactions is a key challenge in nuclear physics research. While mean-field methods can effectively describe the dynamics of low-energy nuclear reactions, their applicability in higher energy regimes is limited due to the neglect of two-body collision correlations. In this study, based on the time-dependent Hartree-Fock (TDHF) method, the quantum relaxation-time approximation (QRTA) is introduced to account for the dissipation effects from the two-body collision in nuclear reactions, resulting in the new version of TDHF-QRx method. The central collisions of O-16 + O-16 at various reaction energies are calculated. The direct manifestation of two-body dissipation is the enhancement of momentum equilibrium and the conversion of collective kinetic energy into excitation energy, when the reaction system possesses sufficient excitation energy and imbalance. A quantitative evaluation of the energy dependence of two-body dissipation is performed, allowing for determining the energy range where the mean-field approximation is reasonably applicable. We show that QRTA effectively compensates for the two-body dissipation mechanism missing in the mean-field approach, providing a valuable guidance for the development of microscopic nuclear reaction dynamics theory.