Do you know how to accurately diagnose and prevent the "heart disease" of aircraft engines? It requires overcoming one of the biggest bottlenecks that constrain their performance—metal fatigue in the blades. Even metals fatigue; spinning thousands of rotations per minute, they run the risk of fracturing over time. Neutron sources can be used for stress testing aircraft engine blades to detect and prevent metal fatigue.
Have you heard of methane hydrates, found distributed in deep seas or permafrost? Safely extracting, storing, transporting, and utilizing methane hydrates requires an understanding of their structure and properties. Methane hydrates are crystalline substances formed by methane and water under high-pressure, low-temperature conditions. Scientists must encase them in thick metal containers to simulate the immense pressure at depths of kilometers underwater. Neutrons are particularly sensitive to the hydrocarbon compounds that make up methane hydrates, allowing research on methane hydrates to be conducted through these thick metal containers.
Studying the performance of electric vehicle batteries, understanding the mechanism of catalysts, investigating the single-particle effects of chips, exploring the spin fluctuations of high-temperature superconducting materials—neutron sources play a crucial role in these fields.
In the Science City of Songshan Lake, Dongguan City, Guangdong Province, China, nestled next to a highway, stands a unique cluster of buildings on a hillside, with the words "China Spallation Neutron Source" prominently displayed. The China Spallation Neutron Source (CSNS) is China's first and the world's fourth pulsed spallation neutron source, providing advanced neutron scattering research and applications for international cutting-edge basic scientific research and various fields of national development strategy. Its successful construction fills the gap in domestic pulsed neutron sources and applications, with its technical and comprehensive performance leading among similar international devices, significantly enhancing China's technological level and independent innovation capabilities in related fields.
Forging an Ideal "Probe"
Physics has undergone three major leaps in the past century, from atomic physics to nuclear physics, and then to particle physics. Over 100 years ago, scientists discovered that atoms are composed of atomic nuclei and electrons, later realizing that atomic nuclei are made up of protons and neutrons. Since the 1960s, scientists have gradually discovered that the protons and neutrons that make up atomic nuclei are composed of even deeper-level particles called quarks.
These three major leaps have yielded fruitful results. As research delves deeper into the microstructures of matter, breakthroughs in material structure theory have been made, driving significant technological inventions and transforming into huge productive forces. The semiconductors, televisions, mobile phones, computers, lasers, and global positioning systems we use today are all developed based on the research achievements of 20th-century physics.
How do we study microstructures? In high school biology classes, we use microscopes to observe pollen and cells. If we want to see even finer structures, we can use electron microscopes. To see even more delicate structures, we need tools like spallation neutron sources and synchrotron radiation sources, which we call super microscopes. As a super microscope, the spallation neutron source uses neutrons as "probes" to peer into the microscopic structures of materials.
Neutrons possess certain characteristics, such as being electrically neutral but having a magnetic moment; they can detect the positions of atomic nuclei and elements such as carbon, hydrogen, oxygen, and nitrogen, which are insensitive to synchrotron radiation; they have strong penetration capabilities, allowing for in-situ research on residual stress and metal fatigue in large engineering components; they can also detect the microscopic dynamic processes of material structures, among other capabilities. Therefore, scientists consider them as the ideal "probe" for exploring the microcosm. When neutrons interact with the atomic nuclei of the object under study and change their direction of motion, scientists can infer the structure of the material by analyzing the trajectory, energy, and momentum changes of scattered neutrons. It's like continuously throwing marbles onto an invisible web; some marbles pass through the web, while others hit it and bounce off in different directions. By recording the trajectories of these marbles, we can roughly infer the shape of the web. If enough marbles are thrown, densely enough and with sufficient force, we can accurately depict the composition of this web.
Constructing Neutron "Factories"
Neutrons actually exist everywhere around us, but these neutrons are confined within atomic nuclei and cannot move freely. To use neutrons as probes, we need free neutrons. Where do free neutrons come from? This requires specialized facilities that produce large quantities of free neutrons, which can colloquially be referred to as neutron-producing "factories." There are mainly two types of such "factories": one is reactor neutron sources, and the other is spallation neutron sources, which use high-energy proton beams to bombard heavy metal targets, causing spallation reactions and generating high-flux pulsed neutron beams. Internationally, advanced neutron sources are gradually shifting from reactors to spallation sources due to their better performance and higher safety.
There's a fundamental law in physics: the smaller the scale you're studying, the higher the energy you need. As research delves into the nucleus and particles, the scale of studying material microstructures becomes smaller, requiring the use of higher-energy particles. Accelerators can produce high-energy particles, and the larger the accelerator, the higher the potential energy it can achieve. This has led to the emergence of various major technological infrastructure projects based on large accelerators, also known as big science facilities.
These big science facilities have distinct scientific and engineering attributes, yielding abundant knowledge innovation and scientific output. The significant benefits of technology spillover and talent aggregation make them key elements of a country's innovation landscape, representing essential tools for national innovation and scientific advancement.
In September 2011, construction began on the China Spallation Neutron Source facility in Dongguan, Guangdong. The first-phase construction includes an 80-million-electron-volt linear accelerator, a 1.6-billion-electron-volt rapid cycling synchrotron accelerator, a target station, and three neutron scattering spectrometers for scientific experiments. Its working principle involves accelerating protons to 1.6 billion electron volts, equivalent to 0.92 times the speed of light, treating the proton beam as "bullets" to bombard heavy metal targets. When the atomic nuclei of the metal target are struck, protons and neutrons are ejected, and scientists "collect" neutrons using special devices to conduct various experiments. The device for the Spallation Neutron Source (SNS) in China is not only colossal but also intricate, with numerous components and a highly complex manufacturing and installation process, overcoming numerous challenges. The mass production of equipment for the device was completed by nearly a hundred cooperating units nationwide, with a localization rate of over 90%, and many devices reaching international advanced levels. In August 2017, the Chinese Spallation Neutron Source successfully obtained a neutron beam that fully met expectations during its first beam operation. In 2018, the construction of the Chinese Spallation Neutron Source was completed with high quality according to the specifications and schedule, thus achieving a significant leap forward in the field of high-current proton accelerators and neutron scattering, providing strong support for basic research and high-tech R&D in materials science, life science, resources and environment, and new energy.
Establishing Cross-platform Collaboration Since the Chinese Spallation Neutron Source entered the formal operation stage after passing the national acceptance, it has completed more than ten rounds of open access, with an annual operation time exceeding 5000 hours, leading in both duration and efficiency among similar international facilities. Currently, it has completed over 1300 scientific research projects, yielding a batch of important scientific achievements, such as lithium-ion batteries, solar cell structures, rare earth magnetism, new high-temperature superconductors, quantum materials, functional films, high-strength alloys, and single-particle effects on chips, providing a crucial research platform for various strategic needs and high-tech industries in the country. In the Guangdong-Hong Kong-Macao Greater Bay Area, eight collaborative spectrometers have been constructed and put into operation.
In recent years, the Chinese Spallation Neutron Source has conducted internal residual stress measurements on domestically-produced high-speed train wheels, providing comprehensive stress data crucial for the safety and speed enhancement of high-speed trains. By utilizing neutron penetration and quantitative identification capabilities for complex compositions, it has explained the new mechanism of creating world-record high-yield strength and good toughness super steels. Through real-time in-situ measurements, it has studied the structural characteristics of automotive lithium-ion batteries and the transport behavior of lithium ions during charge-discharge cycles, providing important data support for enhancing lithium battery performance. By operating atmospheric neutron spectrometers, it has accelerated the simulation of cosmic rays hitting the atmosphere to create neutron irradiation environments, offering important means to solve the failure issues of electronic components in the atmosphere and on the ground, and providing a research platform for aircraft airworthiness certification and aviation safety.
The Chinese Spallation Neutron Source actively promotes the transformation of relevant technological achievements. Boron neutron capture therapy for tumor treatment is a new binary cellular-level precision cancer treatment technology developed using the technology developed by the Chinese Spallation Neutron Source. As the first project to promote the industrialization of Spallation Neutron Source technology, the boron neutron capture therapy project has completed installation and commissioning of clinical equipment at the Dongguan People's Hospital and is about to commence clinical trials.
The second phase of the Chinese Spallation Neutron Source project officially commenced in January 2024. After the completion of the second phase project, the number of spectrometers at the Chinese Spallation Neutron Source will increase to 20, and the power of the accelerator's beam will increase from 100 kilowatts in the first phase to 500 kilowatts. With the completion of new spectrometers and experimental terminals, the equipment research capabilities of the Chinese Spallation Neutron Source will be significantly enhanced, and the precision and speed of experiments will be significantly improved, capable of measuring smaller samples and studying faster dynamic processes, providing a more advanced research platform for frontier scientific research, national major needs, and the development of the national economy.
The completion of the Chinese Spallation Neutron Source coincides with a golden era of large scientific facility development, bearing the important responsibility of developing neutron scattering research and applications in China, providing a crucial engine for national innovation and development, and making contributions to achieving high-level technological self-reliance and self-improvement.
(The author is an academician of the Chinese Academy of Sciences and the general commander of the Chinese Spallation Neutron Source project command)
Cooperation between the China Association for Science and Technology Science Communication Center, the Chen Jiageng Science Award Foundation, and this newspaper.
