The origin of the matter-antimatter asymmetry in the Universe remains an unsolved mystery in our understanding of the world. According to the Sakharov conditions, the simultaneous violation of charge conjugation (C) and charge-parity (CP) symmetry is indispensable. CP violation has been observed in the decays of mesons and baryons, and can be explained by the CP violation mechanism (such as Cabibbo-Kobayashi-Maskawa matrix) within the Standard Model. However, the extent of CP violation provided by the Standard Model is far from sufficient to account for the matter-antimatter asymmetry in the present universe, revealing the existence of new CP violation mechanisms beyond the Standard Model. Thus, the search for CP-violation mechanisms beyond the Standard Model is of significant scientific importance. Exploring experimental signatures of CP violation in low-energy complex systems, such as permanent electric dipole moment (EDM) in atoms, molecules and nuclei, offers complementary correlations with experimental searches at other energy scales, collectively providing a stringent benchmark of Standard Model physics and constraining new physics beyond the Standard Model. In recent years, radioactive molecules, which combine the structural advantages of polar molecules and heavy octupole-deformed nuclei, have brought new opportunities for measuring the nuclear Schiff moment, a sensitive probe for nuclear CP violation. Consequently, spectroscopic studies of radioactive molecules have emerged as a brand new and widely-recognized research frontier, which has subsequently been included in the new long-range plans for nuclear science in both the United States and Europe, sparking intense international competition. Research on the production and spectroscopic measurement of radioactive molecules is also being extensively planned and deployed at major radioactive nuclear beam facilities worldwide. This paper briefly reviews recent progress in the spectroscopic study of radioactive molecules and summarizes ongoing and planned research efforts in this field, both domestically and internationally, while also providing perspectives for future developments.

The study of nuclear clustering lies at the frontier of nuclear physics, providing key insights into effective nuclear interactions and the development of nuclear structure theories. It also plays a crucial role in advancing our understanding of nuclear astrophysical processes, heavy-ion collisions, and the properties of neutron-rich matter. Over the past decade, we have continuously advanced our detection techniques-most notably through the development of large charged-particle telescope arrays-and conducted systematic experimental investigations of cluster structures across a broad range of contexts using both domestic and international nuclear physics facilities, leading to a series of significant breakthroughs. In this review, we first outline the primary experimental methods for exploring clustering phenomena, including approaches for studying the cluster structure of excited states and knockout-reaction-based techniques for probing clustering in the ground state. We then summarize our recent progress, highlighting molecular structures in the excited states of 10,12Be studied by measuring the selective cluster decay, linear-chain molecular states in 14,16C, Bose-Einstein condensate (BEC)like cluster states in 16O, the dineutron-condensate cluster state in 8He probed by measuring the characteristic transition strength and emission of correlated neutron pairs, and surface alpha-clustering in heavy nuclei probed by using the quasi-free (p, p alpha) reaction. We also present a brief outlook on future directions in this field. Molecular cluster structures and BEC-like alpha-condensate states are expected to remain central themes of theoretical and experimental studies in the coming decade. With continued advances in RIB facilities and experimental techniques, studies of molecular cluster structures are anticipated to extend to heavier systems such as O and Ne, while searches for alpha-condensate states involving more alpha clusters-for example, 5 alpha condensate in 20Ne and 6 alpha condensate in 24Mg-are actively underway. Quasi-free (p, p alpha) cluster knockout reactions are being applied to unstable nuclei, and dedicated detector arrays for such measurements are now under development. These cluster knockout studies are also being extended to other clusters (d,t,3He), aiming for a comprehensive understanding of cluster formation in both finite nuclei and infinite nuclear matter. Significant progress has been made in the study of neutron correlations and clusters, but many open questions remain, with a prominent example being the elusive tetraneutron. Future experiments should go beyond resonance energies and widths, and probe internal neutron correlations of multi-neutron systems by directly detecting the decay neutrons. It is of great interest to consider neutron clusters accommodated in a nuclear environment, such as in neutron-rich nuclei, where the neutron correlations will be enhanced. Under such conditions, multiple dineutron clusters may form and further develop into condensate-like cluster states. From an experimental perspective, neutron detector arrays with high resolution and high efficiency for the detection of multiple neutrons are essential, and a new multi-neutron detector array is currently under development in our laboratory.

The hyperfine structure reflects the electromagnetic interactions between the atomic nucleus and the surrounding electrons. Their spectral features simultaneously encode information about both nuclear properties and the structure of atomic and molecular systems. High-precision measurements of hyperfine structures and isotope shifts using advanced laser spectroscopy techniques enable the model-independent extraction of multiple fundamental properties of atomic nuclei, such as spins, magnetic moments, electric quadrupole moments, and charge radii. Such measurements provide critical experimental inputs for the discovery and investigation of exotic phenomena in unstable nuclei, including halo structure, island of inversion, shell evolution, and shape coexistence, as well as for testing nuclear theoretical models. Additionally, the integration of laser spectroscopy with radioactive ion beam facilities has significantly advanced frontier research in atomic and molecular physics, such as experimental validation of quantum electrodynamics, benchmarking the accuracy of atomic and molecular structure calculations, and exploration of fundamental symmetries. In recent years, the continued development of radioactive ion beam facilities has expanded the nuclear chart, enabling experimental access to an increasing number of unstable nuclei. However, the short lifetimes, low production yields, and substantial contamination from stable and long-lived isomers present major challenges for laser spectroscopy measurements. Among various methods, collinear laser spectroscopy, owing to its high spectral resolution, has played an irreplaceable role in studying the exotic structures of unstable nuclei across various mass regions, while also contributing to related research in atomic and molecular physics. It has been widely implemented at major radioactive ion beam facilities worldwide. This review will systematically discuss the measurement principles and methodological features of collinear laser spectroscopy based on fluorescence detection and collinear resonance ionization spectroscopy based on ion detection. It will also emphasize the innovative applications and recent advances of these two techniques in the interdisciplinary research between nuclear physics and atomic and molecular physics.

Experimental and theoretical investigation of the fragmentation reaction in the Fermi-energy domain is currently of particular importance for not only nuclear physics but also some interdisciplinary fields.In the present study,neutron-rich 14C and 16C ion beams at 27.5 MeV/nucleon were used to bombard carbon and polyethylene(CD2)n targets.Energy and angular distributions of the produced fragments were measured.Background events ori-ginating from the carbon content in(CD2)n target were efficiently excluded using an extended E-P plot method.Ex-perimental results are systematically analyzed using the HIPSE-SIMON dynamic model.The comparison reveals that,for the carbon target,the HIPSE-SIMON calculation overestimates the yields of the beam-velocity component for fragments near the projectile and also the energy phase space for fragments far away from the projectile,suggest-ing that fine tuning of the overall interaction profile adopted in the model is required.In contrast,for reactions with the deuteron target,the model calculation can reasonably reproduce the experimental data.The implication of the fragmentation mechanism on the validity of the invariant mass method,as frequently used to reconstruct the cluster-ing resonant structures in light nuclei,is also discussed.

The second 0+excited state at 7.65 MeV in 12C,known as the Hoyle state,is located near the 3-α break-up threshold and possesses a typical BEC-analog structure.This observation has triggered the intensive theoretical studies of the condensation configuration in nuclear systems,typically represented by the THSR wave function.In the mean time,the experimental investigation of the Hoyle-like states in heavier nuclei has been advanced quite slowly,due mostly to the difficulties in detecting multi-fragments in coincidence and the clarification of the reaction-decay mechanisms.We give here a review of the theoretical and experimental progresses in this field by taking into account the latest experimental outcomes for the 4-α resonance in 16O and α+2n+2n resonance in 8He.Some per-spectives are also given towards the possible BEC-like states in neutron-rich systems,which would be of particular importance in exploring the properties of the heavier neutron-rich nuclei and also the neutron stars.

To study the nuclear properties and deformation of neutron-rich cesium isotopes in their ground and isomeric states at the Beijing Rare Isotope Beam Facility (BRIF), optimal resonance ionization schemes and experimental conditions must be predetermined. In this work, we evaluated several three-step laser resonance ionization schemes for the cesium atom, accessing their ionization efficiency and spectral resolution under varying measurement conditions using the high-resolution and high-sensitivity collinear resonance ionization spectroscopy system. As a result, we identified the currently most efficient resonance ionization scheme and optimal experimental conditions, achieving an overall measurement efficiency of 1:400 with a spectral resolution of about 100~MHz. Under this condition, the extracted hyperfine structure parameters of $^{133}$Cs showed excellent agreement with previously reported values. This work establishes a solid foundation for the forthcoming online measurement of neutron-rich cesium isotopes at BRIF.

LACPU, a Large Acceptance Charged particle detector array has been developed at Peking University. This system is capable of simultaneously detecting several direct reaction channels in inverse kinematics, including (d, p), (d, t), (d, 3He), (d, 4He), (d, d), (d, d '), and (d, 6Li), among others, in a single experiment. This paper reports on the solid angles, energy resolution, and particle identification capabilities of LACPU during its commissioning experiment with radioactive ion beams. Additionally, the optical potential parameters of 15C + p and 15C + d, which are essential for analyzing more complex reaction channels, have been extracted from the angular distributions of elastic scattering measured in the first experiment of LACPU.

A RadioFrequency Quadrupole (RFQ) cooler-buncher system was developed and implemented in a collinear laser spectroscopy setup. This system converts a continuous ion beam into short bunches while enhancing the beam quality and reducing the energy spread. The functionality of the RFQ cooler buncher was verified through offline tests with stable rubidium and indium beams delivered from a surface ion source and a laser ablation ion source, respectively. Bunched ion beams with a full width at half maximum of approximately 2 s in the time-of-flight spectrum were successfully achieved with a transmission efficiency exceeding 60

With the recent implementation of a radio-frequency quadrupole (RFQ) cooler-buncher and a multi-step laser resonance ionization technique, our previously developed collinear laser spectroscopy setup has been successfully upgraded into a fully functional collinear resonance ionization spectroscopy system. The new system was fully characterized using a bunched ion beam at 30 keV, during which hyperfine structure spectra of ^85,87Rb isotopes were measured. An overall efficiency exceeding 1:200 (one resonant ion detected for every 200 ions after the RFQ cooler-buncher) was achieved while maintaining a spectral resolution of 100 MHz. Under these conditions, the extracted hyperfine structure parameters and isotope shift for ^85,87Rb show excellent agreement with the literature values. These results demonstrate the system's capability to perform high-resolution and high-sensitivity laser spectroscopy of neutron-rich Rb isotopes, which are expected to be produced at the Beijing Radioactive Ion-beam Facility at a rate of approximately 100 particles per second.

A new inelastic excitation and cluster-decay experiment was conducted to investigate the negative-parity linear-chain structure in C-16. The helium and beryllium isotopes emitted from the highly excited states of C-16 and the recoil target deuteron were detected in coincidence. The C-16 excitation-energy spectra associated with different decay paths were reconstructed using the invariant mass method. Owing to the newly reconfigured detector setup, the detection acceptance was extended to a higher excitation-energy range, allowing a number of new resonant states to be observed beyond the previously reported pi(2)sigma(2)-bond positive-parity linear-chain band. Based on comparison with the AMD calculations for both resonance energies and relative decay widths, these newly observed states can be tentatively assigned as the 1(-), 3(-), 5(-) and 7(- )members of the negative-parity linear-chain molecular rotational band. More experimental studies are expected to directly measure the spins of these states.

To study the nuclear properties and deformation of neutron-rich cesium isotopes in their ground and isomeric states at the Beijing Rare Isotope Beam Facility (BRIF), optimal resonance ionization schemes and experimental conditions must be predetermined. In this study, we evaluated several three-step laser resonance ionization schemes for cesium atoms to access their ionization efficiency and spectral resolution under varying measurement conditions using high-resolution and high-sensitivity collinear resonance ionization spectroscopy system. Hence, we identified the currently most efficient resonance ionization scheme and optimal experimental conditions, achieving an overall measurement efficiency of 1: 400 with a spectral resolution of about 100 MHz. Under this condition, the extracted hyperfine structure parameters of Cs-133 showed excellent agreement with previously reported values. This study establishes a solid foundation for the forthcoming online measurement of neutron-rich cesium isotopes at BRIF.

Invariant-mass spectroscopy has been performed to search for possible resonance states in the loosely bound neutron-rich 15 C nucleus.By detecting alpha and 11 Be in coincidence,we reconstruct the excitation energy spectrum for 15 C.To estimate the physical background from non-resonant prompt alpha particles,we employ a recently proposed weighted event-mixing method with phenomenological reduced weighting at around the alpha-decay threshold to account for the depletion in the prompt alpha's contribution owing likely to the Coulomb final-state interactions.A new weighted mixed-event method that focuses on a robust treatment of the Coulomb effect is also proposed.Through fitting the spectrum using the background estimated with these two methods,up to two resonance state candidates are proposed.Further experiments with improved statistics and theoretical calculations are called for to confirm the se resonance states.

近期在中国原子能科学研究院北京串列加速器核物理国家实验室开展的 16O + 12C 非弹散射实验，给出了 16O 中存在 4-𝛼 玻色凝聚状态的新证据。实验采用多套双面硅微条带电粒子望远镜，首次在 16O 衰变中实现了 4 个 𝛼 粒子的准确识别 (Particle Identification, PID) 和符合测量。在此基础上获得了高分辨的反应 𝑄 值谱并重建了清晰的 4-𝛼 共振态。其中在阈值附近观察到 4 个高显著度 (大部分高于 5𝜎) 的共振态，它们按照12C(Hoyle state) + 𝛼 的特征模式衰变，与理论预言的类 Hoyle-BEC 结构及其转动带特征相一致。本观测结果将推动进一步的理论研究，实验上也需要对上述共振态做更多物理量的观测。

A digital data-acquisition system based on XIA LLC products was used in a complex nuclear reaction experiment using radioactive ion beams. A flexible trigger system based on a field-programmable gate array (FPGA) parametrization was developed to adapt to different experimental sizes. A user-friendly interface was implemented, which allows converting script language expressions into FPGA internal control parameters. The proposed digital system can be combined with a conventional analog data acquisition system to provide more flexibility. The performance of the combined system was verified using experimental data.

The basic properties of atomic nuclei including spins,magnetic moments,electric quadrupole moments and charge radii,are sensitive probes to different aspects of exotic nuclear structure,and are also important to investigate the unrevealed nature of interaction between nucleons.Based on multidiscipline,laser spectroscopy is a unique tool to precisely measure the basic nuclear properties mentioned above in a nuclear-model independent way by measuring the hyperfine structure of atoms,ions,or molecules,which has played an important role in the study of exotic nuclear structures across the different regions of the nuclear chart.Basic principles of laser spectroscopy and various types of experimental devices are expounded after the brief history of the hyperfine structure.Furthermore,advantages of utilizing laser spectroscopy in the study of nuclear struc-ture are briefly introduced by taking the radioactive neutron-deficient Pb region as an illustration.In addition,current condi-tion of collinear laser spectroscopy setup has been systematically reviewed,together with the latest progress on collinear res-onance ionization spectroscopy offline devices at Peking University.Finally,the developing status and ongoing plan of laser spectroscopy devices for current and future radioactive ion beam facilities in China have been put forward,and the broad pro-spects of laser spectroscopy in unstable nuclear properties and the fundamental symmetries based on molecular spectroscopy are interpreted.

Nucleus is essentially composed of protons and neutrons, which are commonly known as nucleons. Interestingly, some of nucleons may group together and exhibit collective behavior inside a nucleus. Such clustering effects have been known since the early stages of nuclear physics because of the observation and description of α-cluster decay from many heavy nuclei. Subsequent studies demonstrated that cluster structures exist in many nuclear systems, especially in weakly bound or excited states, and are complementary to the shell-like structures. In this review article, we provide a brief historical recall of the field, and follow it with a conceptual and logical description of the major theoretical models that have been frequently applied in the literature to describe nuclear clustering. Experimental methods and progress are outlined, recent outcomes are emphasized, and perspectives relevant to future studies of heavy neutron-rich systems are discussed.

The past three decades have witnessed the emergence of exotic structures and dynamics in weakly bound unstable nuclei located in the rapidly expanding nuclear chart. Examples include halo and cluster structures, shell evolution incorporating the shift of the nuclear magic numbers, new modes of collective motion, strong coupling to the continuum and new reaction–decay mechanisms. The progress in this fast-evolving field and its deep impacts on several key interdisciplinary realms will be reviewed in this article, together with perspectives for the future exploration of the heavier neutron-rich region. This article reviews the exotic structures and dynamics that emerge in weakly bound unstable nuclei, highlighting their deep impacts on several key interdisciplinary fields. Additionally, it outlines prospects for future exploration of the heavier neutron-rich region.

We report here the first observation of the 0(2)(+) state of He-8, which has been predicted to feature the condensatelike alpha + (2)n + (2)n cluster structure. We show that this state is characterized by a spin parity of 0(+), a large isoscalar monopole transition strength, and the emission of a strongly correlated neutron pair, in line with theoretical predictions. Our finding is further supported by the state-of-the-art microscopic alpha + 4n model calculations. The present results may lead to new insights into clustering in neutron-rich nuclear systems and the pair correlation and condensation in quantum many-body systems under strong interactions.