The experimental nuclear physics group (ENPG) led by Professor Zhigang Xiao from the Department of Physics at Tsinghua University has made a groundbreaking observation in heavy-ion nuclear reactions, specifically noting an isotopic "ping-pong" emission phenomenon. This phenomenon, which occurs in an extremely small spatial scale of femtometers (10^-15 meters) and a temporal scale of zeptoseconds (10^-21 seconds), involves the dynamic and compositional correlation of particles emitted during the reaction, providing a novel experimental approach to studying the transport properties of nucleon isospin degrees of freedom. The ENPG utilized a compact heavy-ion experimental spectrometer, named CSHINE (Compact Spectrometer for Heavy IoN Experiment), which they developed independently. This equipment was employed at the RIBLL1 terminal of the National Major Scientific Facility HIRFL (Heavy Ion Research Facility in Lanzhou) to conduct a coincidence measurement of charged particles in the 25 MeV/u Kr+Pb reaction. By analyzing the energy spectra and yield ratios of tritium and helium-3 particles that were emitted in coincidence with medium-mass fragments (atomic mass numbers ranging from 6 to 12), the researchers were able to examine the fine characteristics of the thermodynamic relaxation and isospin degree of freedom relaxation in the nuclear reaction process. A key finding of the experiment was the discovery of a scaling phenomenon in the energy spectra of tritium and helium-3, coupled with a notable anti-correlation between their yield ratios and the neutron-to-proton ratio (N/Z) of the associated medium-mass fragments. Specifically, if the first emitted fragment is neutron-rich, the accompanying light particles tend to be neutron-poor, as indicated by a lower yield ratio of tritium to helium-3. Conversely, if the fragment is proton-rich, the light particles are more likely to be neutron-rich, resulting in a higher yield ratio. This behavior is akin to the back-and-forth motion of a ping-pong ball, hence the term "ping-pong" emission. This phenomenon suggests a dynamic and reciprocal exchange of isospin during the particle emission process, which is a significant insight into the mechanisms governing isospin dynamics and nucleon clustering in nuclear reactions. Further analysis revealed that the N/Z ratio of the residual part of the reaction system after particle emission remained close to the initial N/Z ratio of the system, indicating an isospin equilibrium effect. This effect, which is a universal phenomenon driven by symmetry energy, is also observed in the fragmentation decay of superheavy nuclei and neutron-induced fission of heavy nuclei. The Tsinghua University experiment confirms that this isospin equilibrium effect persists even in the high-excitation systems formed by heavy-ion collisions at Fermi energies. This discovery offers new perspectives on the study of isospin dynamical evolution and nucleon clustering emission mechanisms. It also provides a novel method for constraining the symmetry energy of atomic nuclei and testing the transport models of heavy-ion nuclear reactions. The findings were published in a rapid communication in the prestigious international nuclear physics journal *Physical Review C* (Phys. Rev. C, 107, L041601, 2023). The research was primarily conducted by Tsinghua University's ENPG, with significant contributions from Professor Li Ou's team at Guangxi Normal University, who were responsible for the transport model calculations. Dr. Yijie Wang, a postdoctoral fellow at Tsinghua University, Professor Zhigang Xiao, and Professor Li Ou are the co-corresponding authors of the paper. The work was supported by the Ministry of Science and Technology, the National Natural Science Foundation of China, Tsinghua University's independent research program, and the open fund of the National Laboratory of Heavy Ion Accelerator in Lanzhou. The publication can be accessed through the following link: [Phys. Rev. C, 107, L041601 (2023)](https://doi.org/10.1103/PhysRevC.107.L041601). This research not only advances the understanding of fundamental nuclear physics but also has implications for the broader field of nuclear science, including the development of more accurate nuclear reaction models and the refinement of symmetry energy parameters. The "ping-pong" emission phenomenon observed by the ENPG provides a unique experimental signature that can be used to probe the intricate dynamics of isospin in nuclear reactions, potentially leading to new insights and applications in nuclear technology and astrophysics.