We present the design, implementation, and performance of a fast-switching gating grid driver (GGD) for the S pi RIT Time Projection Chamber, optimized for heavy-ion collision experiments. The GGD controls the wire gating grid to transmit drift electrons from nuclear reactions while blocking ion backflow and background from non-interacting beam particles. A GGD circuit with matched metal-oxide-semiconductor field-effect transistors (MOSFET) and tunable capacitors and resistors enables rapid, low-noise transitions between open and closed states. Bench tests and in-situ tests with the Time Projection Chamber confirm reliable operation with minimal pickup noise. In the 2016 campaign, GGDs using surface-mounted resistors exhibited limited operational lifetimes. For the 2024 campaign, we incorporated anti-surge resistors with higher inductive damping. The new resistors reduced switching noise and resulted in shorter noise decay times. These improvements enabled robust operation at high event rates, achieving stable performance over extended beam times.

Short-range correlation (SRC) in nuclei refers to nucleons forming temporally correlated pairs in close proximity, giving rise to the high momentum of the nucleons beyond the Fermi surface. It has been reported that bremsstrahlung gamma production from the neutron-proton process in heavy-ion reactions provides a potential probe to the SRC abundance in nuclei. In this paper, we present in detail the precision measurement of bremsstrahlung gamma rays in 124Sn + 124Sn reactions at 25 MeV/nucleon using the Compact Spectrometer for Heavy IoN Experiment (CSHINE). A comprehensive experimental and analysis framework is established to ensure the reliability and robustness of the extracted results. Background contributions are evaluated and subtracted using independent methods, and the consistency of the analysis is systematically validated. By comparing the experimental gamma spectrum with isospin-dependent Boltzmann-Uehling-Uhlenbeck simulations, the high momentum tail (HMT) fraction of RHMT = (20 +/- 3)% is derived in 124Sn nuclei. This work provides a detailed and validated experimental framework for extracting SRC information from bremsstrahlung gamma-ray emission and demonstrates the feasibility of studying nucleon SRCs with high precision in low-energy heavy-ion collisions.

With the newly built neutron wall on the compact spectrometer for heavy ion experiment (CSHINE), the n-n correlation function in the reactions of 124Sn + 124Sn at 25 MeV/u has been measured. The cross talk effect is corrected using a detailed Geant 4 simulation. The n-n correlation function has been fitted by LL model assuming a Gaussian source. the n-n scattering length and effective range (f0 nn, 0dnn), as well as the reduced space-time size R(0) of the neutron emission source are simultaneously extracted as (18.9-1.2+1.3 fm, 1.9-1.0+1.3 and 4.12 ± 0.12 fm respectively. The results demonstrate the potential to pin down the charge symmetry breaking of nuclear force with femtoscopy correlation at improved resolution, and highlight the perspective of the future studies on isospin dynamics in heavy ion reactions.

Femtoscopic interferometry is a powerful tool for probing the spatio-temporal evolution of emission sources in heavy-ion collisions. A major challenge in the field is formulating a self-consistent description of the source function, final-state interactions between the particle pair, and interactions inherent to the source itself. To address this, we have developed a novel Monte Carlo model for calculating two-particle correlation functions in a classic framework. The model incorporates self-consistently the emission source of thermal equilibrium and three-body final state interactions. Application of the model shows satisfactory fit to experimental data, revealing that the correlation function is highly sensitive to the source's spatio-temporal extent. In contrast, the temperature parameter governing the emitted particles' energy spectra has a negligible influence. Our approach offers the potential to extract the spatio-temporal information from the emission source, thereby advancing the applicability of femtoscopic interferometry in the Fermi energy domain.

Development of efficient and durable oxygen reduction reaction (ORR) electrocatalysts is of great interest yet remains challenging. Herein, we predicted and screened a bilayer graphite carbon-supported Ir-N4/Fe-N4 catalyst with high ORR activity using density functional theory calculations. Subsequently, various bimetallic single atom supported on 3D ordered macroporous carbon were rationally designed and experimentally synthesized via a colloidal microsphere template-confined reaction method. As anticipated, the resulting Ir-N4/Fe-N4 bimetallic single-atom catalysts (IrFe-SACs) exhibit superior ORR activity and durability, reaching a half-wave potential of 0.928 V. The IrFe-SACs also demonstrate outstanding performance in Zn-air batteries, including a high discharge power density (314 mW cm⁻2) and excellent cycling stability ( 1650 cycles over 550 h). Further experimental characterizations and theoretical analysis reveal that introducing interlayer-adjacent Ir-N4 sites facilitates the transition of Fe-N4 from a low-spin state to a medium-spin state, which optimizes the spin polarization of Fe 3d orbitals and enhances the non-localization of the Fe–O/OH molecular orbital, thereby significantly improving the ORR intrinsic activity and durability of atomic Fe-N4 sites.

The Richardson-Lucy algorithm is applied to reconstruct the three-dimensional source function of identical pions from their two-particle correlation functions. The algorithm's performance is first evaluated through simulations with Gaussian-type initial source functions. Its imaging quality and robustness are further demonstrated with experimental data from Au+Au collisions at 1.23 A GeV, collected by the HADES Collaboration. Additionally, using UrQMD simulations of Pb+Pb collisions at 1.5 A GeV, we show that the deblurred source functions exhibit sensitivity to the initial neutron skin thickness of the colliding nuclei. This highlights the potential of the Richardson-Lucy algorithm as a tool for probing the neutron density distribution in heavy nuclei.

Development of highly active and stable acidic oxygen evolution reaction catalyst is very important for efficient water splitting while remains challenging. Herein, we report a highly ordered RuO2/WO3 inverse opals (IOs) catalyst to address the bottleneck problem of see-saw relationship between activity and stability, in which the crystalline and corrosionresistant WO3 facilitates electron transport and stabilizes RuO2, whereas the lattice mismatch-induced amorphousdominated RuO2 provides abundant unsaturated coordination sites to enhance the acidic oxygen evolution reaction (OER) activity. Consequently, the RuO2/WO3 IOs demonstrates outstanding acidic OER performance in terms of a low overpotential of 180 mV to reach 10 mAcm-2, and excellent stability for maintaining 100 hours continuous test. Experimental characterizations and density functional theory calculations reveal that interface coupling between WO3 and RuO2 can enhance the spin polarization of electrons and increase the overlaps of the electronic projected density of states between the Ru d orbitals of active metal and the O p orbitals of oxygen intermediates, facilitating OER pathway to switch from lattice oxygen mechanism to adsorbate evolution mechanism, which significantly decreases the reaction energy barrier of OER process. Meanwhile, the rich oxygen vacancies and WO3 supports in the heterostructures could inhibit the over-oxidation of Ru species, so as to enhance the activity and stability simultaneously.

The neutron-neutron (nn) correlation function has been measured in 25  MeV/u ^{124}Sn+^{124}Sn reactions. Using the Lednický-Lyuboshitz approach, the nn scattering length and effective range (f_{0}^{nn}, d_{0}^{nn}), as well as the reduced space-time size R^{(0)} of the neutron emission source are simultaneously extracted as (18.9_{-1.2}^{+1.3}  fm, 1.9_{-1.0}^{+1.3}  fm) and 4.12±0.12  fm, respectively. The measured nn scattering length is consistent with the results obtained in the low-energy scattering ^{2}H(π^{-},γ)2n, indicating heavy-ion collisions can serve as an effective approach for measuring nn interactions and further investigating the charge symmetry breaking of nuclear force. The space-time size extracted from momentum-gated correlation functions exhibits clear dependence on the pair momentum, with R^{(0)}=2.8±0.1  fm and 4.9±0.2  fm being determined for the high and low momentum neutrons, respectively.

By combining femtoscopic interferometry with an optical deblurring algorithm, we present a novel method to image the source in heavy-ion collisions (HICs), while simultaneously determining the interaction strength between particle pairs. The spatial distribution of the emission source has been reconstructed for protons (p) and antiprotons ( p ) from the respective pp and pp correlation functions in Au+Au collisions at SNN=200 GeV. Within experimental uncertainties, protons and antiprotons share the same freeze-out distribution showing higher density in the center compared to the widely assumed Gaussian shape. The results evidence the matter-antimatter symmetry in coordinate space at the freeze-out moment before the nucleons are fully randomized in the collisions.

The emission of neutrons from heavy ion reactions is an important observable for studying the asymmetric nuclear equation of state and the reaction dynamics. A 20-unit neutron array has been developed and mounted on the compact spectrometer for heavy ion experiments (CSHINE) to measure the neutron spectra, neutron- neutron and neutron-proton correlation functions. Each unit consists of a 15 x 15 x 15 cm3 plastic scintillator coupled to a cent = 52 mm photomultiplier. The Geant4 simulation with optical process is performed to investigate the time resolution and the neutron detection efficiency. The inherent time resolution of 212 ps is obtained by cosmic ray coincidence test. The n-y discrimination and time-of-flight performance are given by 252 Cf radioactive source test and beam test. The neutron energy spectra have been obtained in the angular range 30 degrees <= B lab <= 51 degrees in the beam experiment of 124 Sn + 124 Sn at 25 MeV/u with CSHINE.

The isovector reorientation (IVR) effect of deuteron scattering on heavy target provides a novel means to probe the nuclear isovector potential, which gives rise to the nuclear symmetry energy. The simulation studies on the experimental measurement of IVR effect using the SAMURAI terminal at RIKEN Nishina center have been performed to demonstrate the feasibility of the experiment. By introducing a well-designed polarimeter to detect the p(d⃗, d)p elastic scattering, monitoring of the tensor polarization of the deuteron beam can be implemented. The protons and neutrons produced by the breakup of polarized deuterons scattering off heavy targets are designed to be measured by proton drift chamber (PDC) combined with the SAMURAI magnet and NEBULA (Neutron-detection system for Breakup of Unstable-Nuclei with Large Acceptance) detector, respectively. The detector responses are simulated using GEANT4 framework, where the events of the deuteron elastic breakup are generated by an Improved Quantum Molecular Dynamics model. The results of reconstructing the deuteron breakup events demonstrate the feasibility of detecting the IVR effect at SAMURAI with both longitudinal and transverse tensor polarized deuteron beams with a polarization degree of approximately 80

The linear response of CsI(Tl) crystals to γ-rays plays a crucial role in their calibration, as any deviation from linearity can introduce systematic errors not negligible in the measurement of γ energy spectra, particularly at high energies. In this study, the responses of CsI(Tl) crystals to high-energy photons up to 20 MeV are investigated using quasi monochromatic γ beam provided by the Shanghai Laser Electron Gamma Source. The spectra are folded using a detector filter implemented by Geant4. Both quadratic and linear fits to six energy points are used to assess the linearity of the CsI(Tl) detector. The results demonstrate that the difference between the linear and non-linear fits is at the level of 4%. Applying these findings to the γ hodoscope of the Compact Spectrometer for Heavy Ion Experiment (CSHINE), the potential systematic uncertainties caused by CsI(Tl) non-linearity are evaluated. This work provides a comprehensive calibration methodology for employing CsI(Tl) crystal to detect high energy γ-rays.

Revealing the neutron density distribution in the nucleus is one of the crucial tasks of nuclear physics. Within the framework of the ultrarelativistic quantum molecular dynamic model followed by a correlation afterburner program, we investigate the effects of the initial neutron density distribution on the charged-pion yield ratio π−/π+, the two-pion momentum correlation function, and the emission source dimension. It is found that the π−/π+ ratio is sensitive to the initial neutron density distribution and the impact parameter, especially for collisions at large impact parameter. However, the charge splitting in the correlation functions between positively π+π+ and negatively π−π−, as well as the source radii and volumes extracted exhibit a stronger dependence on the initial neutron density distribution, but a weaker dependence on the impact parameter. The present study highlights that π+π+ and π−π− correlation functions in heavy-ion collisions could be used to probe the initial neutron density distribution of nuclei.

The neutron richness of the light charged particles emitted out of the fission plane in heavy ion reactions has been experimentally investigated via the production of A=3 mirror nuclei in ^86 Kr + ^nat Pb reactions at 25 MeV/u. The energy spectra and angular distributions of triton (t) and ^3 He in coincidence with two fission fragments are measured with the Compact Spectrometer for Heavy IoN Experiment (CSHINE). The energy spectrum of ^3 He is observed harder than that of triton in the fission events, in accordance with the phenomena reported as “ ^3 He-puzzle” in inclusive measurements. With a data-driven energy spectrum peak cut scenario, it is observed that the yield ratio R(t/^3He) increases with the angle to the fission plane, showing an enhancement of neutron-rich particle emission from out-of-fission-plane. A qualitative comparison with the transport model calculations suggests that this observation may serve as a new probe for the nuclear symmetry energy.

Atomic nuclei and dense nucleonic matter in neutron stars exhibit short-range correlations (SRCs), where nucleons form temporally correlated pairs in close proximity beyond mean-field approximation. It is essential to make precision measurement of the fraction of SRC since it carries the signature of underlying quark dynamics in nuclear medium. In this article, we present the first high-precision measurement of neutron-proton bremsstrahlung γ -ray emission from the symmetric Sn 124 + Sn 124 reactions at 25 MeV/u. From the observed spectral hardening, the precise SRC fraction in the Sn 124 nucleus is extracted to be ( 20 ± 3 ) % . This result provides a statistically unambiguous evidence of SRCs and demonstrates that low-energy heavy-ion collisions offer an approach to studying nuclear structure in connection with quark-level dynamics.

We developed a dedicated data analysis framework for silicon strip detector telescopes (SSDTs) of the Compact Spectrometer for Heavy-IoN Experiments (CSHINE) that addresses the challenges of processing complex signals. The framework integrates advanced algorithms for precise calibration, accurate particle identification, and efficient event reconstruction, aiming to account for critical experimental factors such as charge-sharing effects, multi-hit event resolution, and detector response nonuniformity. Its robust performance was demonstrated through the successful analysis of light-charged particles in the 25 MeV/u ^86 Kr + ^124 Sn experiment conducted at the first Radioactive Ion Beam Line in Lanzhou, allowing for precise extraction of physical observables, including energy, momentum, and particle type. Furthermore, utilizing the reconstructed physical information, such as the number of effective physical events and energy spectra to optimize the track recognition algorithm, the final track recognition efficiencies of approximately 90 % were achieved. This framework establishes a valuable reference methodology for SSDT-based detector systems in heavy-ion reaction experiments, thereby significantly enhancing the accuracy and efficiency of data analysis in nuclear physics research.

The energetic bremsstrahlung photons up to 100 MeV produced in heavy ion collisions can be used as a sensitive probe for short-range correlation in atomic nuclei. The energy of the γ -rays can be measured by collecting the Čerenkov light in the medium induced by the fast electrons generated in the Compton scattering or electromagnetic shower of the incident γ ray. Two types of detectors based on pure water and lead glass as sensitive materials were designed for this purpose. The γ response and optical photon propagation in the detectors were simulated based on electromagnetic and optical processes in Geant4. The inherent energy resolutions of 0.022(4)+0.51(2)/E_γ^1/2 for water and 0.0026(3)+0.446(3)/E_γ^1/2 for lead glass were obtained. The geometry sizes of the lead glass and water were optimized to 30 cm × 30 cm × 30 cm and 60 cm × 60 cm × 120 cm, respectively, to detect high-energy γ -rays at 160 MeV. The Hough transform method was applied to reconstruct the direction of the incident γ -rays, providing the ability to experimentally distinguish the high-energy γ -rays produced in the reactions on the target from random background cosmic-ray muons.