Recently, researchers and collaborators of the Institute of Modern Physics of the Chinese Academy of Sciences have made important progress in the research of the microscopic mechanism of heavy ion cancer treatment. They observed for the first time the intermolecular energy and proton transfer cascade mechanism caused by heavy ion irradiation in biomolecule clusters, which is considered an important reason for the excellent biological effects of heavy ion cancer treatment. The related results were recently published as a highlight paper in the physics journal "Physical Review X" and reported online in the American Physical Society's "Physics" journal. Heavy ion cancer treatment is a radiation therapy technique that uses heavy ion beams to kill cancer cells, and is currently the most advanced radiation therapy method. Since scientists proposed using heavy ions to treat tumors in 1946, over 50000 patients worldwide have received heavy ion therapy. Xu Shenyue, a researcher at the Institute of Modern Physics of the Chinese Academy of Sciences, said: "At the same dose, heavy ions are 2-3 times more powerful than traditional radiotherapy methods such as X-ray, and heavy ion radiotherapy can directly lead to double strand breaks in tumor cell DNA, with significantly higher biological effects. However, it is not clear for a long time what microscopic mechanisms play an important role in it." To further explore this problem, researchers developed advanced mixed cluster source technology, selecting pyrimidine molecule, a basic structural unit in DNA, as the model. The research team combined water molecules and pyrimidine molecules to prepare controllable sized hydrated pyrimidine clusters to simulate the tissue environment of the body. The experiment was conducted on the cooling storage ring of the Lanzhou Heavy Ion Accelerator and the 320 kV high charge state ion comprehensive research platform. The research team observed for the first time that when heavy ions irradiate water molecules, the ionized water molecules in the inner shell transfer energy to pyrimidine molecules, causing pyrimidine molecules to ionize and release a low-energy electron. This process will further induce proton transfer between water molecules, producing hydroxyl radicals that are also lethal. It is generally believed that ionized water molecules in the inner shell do not directly act on DNA, but rather decay through their own dissociation. But this study suggests that ionized water molecules in the inner shell of body tissues can directly act on DNA to ionize it, while also producing lethal secondary particles around DNA. This process increases the likelihood of both DNA strands being simultaneously disrupted. In addition, the proportion of ionization of the inner shell of water molecules caused by heavy ion irradiation is significantly higher than other types of radiation such as electrons, X-rays, and protons. The microscopic mechanism discovered this time is an important reason for the high biological effects of heavy ions. This study can help us gain a deeper understanding of the molecular mechanisms of radiation damage, which will aid in optimizing cancer treatment strategies and promoting the development of new radiation therapy technologies in the future Ma Xinwen, a researcher at the Institute of Modern Physics of the Chinese Academy of Sciences, said. The work was led by the Institute of Modern Physics of the Chinese Academy of Sciences and jointly completed by Irkutsk State University of Russia, Heidelberg University of Germany, University of Science and Technology of China, Xi'an Jiaotong University and Lanzhou University. The research was supported by the key research and development plan of the Ministry of Science and Technology, the Chinese Academy of Sciences, the National Natural Science Foundation of China and the Ministry of Science and Education of the Russian Federation. (New Society)