Source: People's Daily
Author: Chen Hesheng, Academician of the Chinese Academy of Sciences, Commander-in-Chief of the China Spallation Neutron Source Engineering Headquarters
The picture shows the China Spallation Neutron Source Station
The picture shows the China Spallation Neutron Source Ring Equipment Building. Courtesy of China Spallation Neutron Source Graphic: Cai Huawei
Do you know about combustible ice that is found in deep-sea or terrestrial permafrost? To safely mine, store, transport and utilize combustible ice, you need to understand its structure and properties. Combustible ice is a crystalline substance formed by methane and water at high pressures and low temperatures, and scientists must place it in a thick metal container to simulate the enormous pressure at a depth of thousands of meters. Neutrons are the most sensitive to the hydrocarbons that make up combustible ice, and the spallation neutron source allows the study of combustible ice through thick metal containers.
Spallation neutron sources can play a key role in studying the battery performance of electric vehicles, studying the mechanism of action of catalysts, studying the single-event effect of chips, and studying the spin fluctuations of high-temperature superconducting materials.
In Songshan Lake Science City, Dongguan City, Guangdong Province, close to the expressway, there is a group of buildings built by the mountain with unique shapes, and on the hillside stands the words "China Spallation Neutron Source". The China Spallation Neutron Source (CSNS) is the first pulsed spallation neutron source in mainland China and the fourth in the world, providing advanced neutron scattering research and applications for many fields of international frontier basic scientific research and national development strategies. Its successful construction has filled the gap in the domestic pulsed neutron source and application field, and its technology and comprehensive performance have entered the advanced ranks of similar devices in the world, which has significantly improved the technical level and independent innovation ability of the mainland in related fields.
Neutrons are ideal "probes" to explore the microscopic world
Physics has undergone three major leaps in the past century, from atomic physics to nuclear physics and then to particle physics. More than 100 years ago, scientists discovered that the atom is composed of nuclei and electrons, and later discovered that the nucleus is composed of protons and neutrons, and since the 60s of the 20th century, scientists have gradually discovered that the protons and neutrons that make up the nucleus are composed of deeper particles - quarks.
It should be said that these three great leaps have produced fruitful results, and in the process of continuously deepening the research to a new level of material microstructure, major breakthroughs have been made in the theory of material structure, and major technological inventions have been driven into huge productive forces. The semiconductors, televisions, mobile phones, computers, lasers, and global positioning systems we use today are all based on the results of 20th-century physics.
How do we study microstructure? We used a microscope in middle school biology class to look at pollen, to look at cells. If you want to see a finer structure, you can use an electron microscope. More elaborately, we use spallation neutron sources, synchrotron radiation sources, etc., which we call super microscopes. As a super microscope, the Spallation Neutron Source uses neutrons as "probes" to see through the microstructure of materials.
Neutrons have some characteristics, such as being uncharged but having a magnetic moment; they can detect the position of atomic nuclei and light elements that are not sensitive to synchrotron radiation, such as carbon, hydrogen, oxygen, nitrogen, etc.; they have a very strong penetrating ability, and can be used to study the residual stress and metal fatigue of large engineering components in situ; and they can detect the microscopic dynamic processes of material structure. As a result, it is regarded by scientists as an ideal "probe" for exploring the microscopic world. When neutrons interact with the nucleus of the object of study to change the direction of motion, scientists can deduce the structure of matter by analyzing the trajectories of scattered neutrons, changes in energy and momentum. It's like we keep throwing marbles into an invisible net, some of which go through the net, and some of which hit the net and bounce at different angles. If you record the movement of these marbles, you can roughly guess the shape of the net. If the marbles are thrown enough, densely enough, and strong enough, the composition of the net can be accurately delineated.
Big science devices are important weapons of the country and weapons of science and technology
Neutrons are actually everywhere around us, but these neutrons are bound to the nucleus of the atom and cannot move freely. If we want to use neutrons as probes, we need free neutrons. Where do free neutrons come from? This requires a device that produces a large number of free neutrons, which can be colloquially called a "factory" that produces neutrons. There are two main types of such "factories": one is the reactor neutron source, and the other is the spallation neutron source, which uses a high-energy proton beam to bombard a heavy metal target, and the spallation reaction occurs, resulting in a high-flux, short-pulse neutron beam. Advanced neutron sources in the world are gradually shifting from reactors to spallation neutron sources because of their better performance and higher safety.
There is a basic law of physics that the smaller the scale, the higher the amount of energy required. As the study of the structure of matter goes deeper into the level of atomic nuclei and particles, the scale of studying the microstructure of matter becomes smaller and smaller, and it is necessary to use particles with higher and higher energy. Accelerators can produce high-energy particles, and the larger the accelerator, the higher the energy is likely to be, which has given rise to a variety of major scientific and technological infrastructures based on large accelerators, also known as big science devices.
These large scientific devices have distinct dual attributes of science and engineering, with fruitful output of knowledge innovation and scientific achievements, and the benefits of technology spillover and talent gathering are very significant, so they often become the key elements of the national innovation highland, and are the important weapons of the country and the weapon of science and technology.
In September 2011, the construction of the China Spallation Neutron Source Facility started in Dongguan, Guangdong. The first phase of construction includes an 80 million electronvolt linear accelerator, a 1.6 billion electronvolt fast cyclic synchrotron, a target station, and three neutron scattering spectrometers for scientific experiments. It works by accelerating protons to 1.6 billion electron volts, a speed equivalent to 0.92 times the speed of light, and using the proton beam as a "bullet" to bombard heavy metal targets. Protons and neutrons are knocked out of the nuclei of metal targets, and scientists use special devices to "collect" neutrons and carry out various experiments.
The Spallation Neutron Source is not only extremely large, but also has a large number of components, an extremely complex process, and many difficulties in manufacturing and installation. The mass production of various equipment of the device has been completed by nearly 100 cooperative units across the country, with a localization rate of more than 90%, and many equipment have reached the international advanced level. In August 2017, the China Spallation Neutron Source successfully obtained a neutron beam that fully met expectations for the first target. In 2018, the China Spallation Neutron Source completed the project construction task with high quality according to the indicators and construction period, and since then it has achieved a major leap in the field of strong current proton accelerator and neutron scattering, providing strong support for basic research and high-tech research and development in material science, life science, resources and environment, new energy, etc.
The Spallation Neutron Source is a large-scale crossover platform that provides advanced neutron scattering research and applications
Since the China Spallation Neutron Source passed the national acceptance and entered the official operation stage, it has completed 11 rounds of opening, with an annual operation time of more than 5,000 hours, and the opening time and efficiency are at the leading level of similar devices in the world. At present, more than 1,300 scientific research projects have been completed, and a number of important scientific achievements have been made, such as lithium-ion batteries, solar cell structures, rare earth magnetism, new high-temperature superconductivity, quantum materials, functional thin films, high-strength alloys, chip single event effects, etc., providing key research platforms for the strategic needs of many fields and high-tech industries in China. In the Guangdong-Hong Kong-Macao Greater Bay Area, the Spallation Neutron Source has built another 8 cooperative spectrometers, which have been put into operation one after another.
In recent years, the China Spallation Neutron Source has measured the internal depth residual stress of domestic high-speed railway wheels, and given the complete stress data of high-speed rail wheels, which is of great significance for the safety and speed of high-speed rail; the neutron penetration ability and the quantitative identification ability of complex components have been used to explain the new mechanism of super steel with high yield strength and good toughness, which has set a world record; through real-time in-situ measurement, the structural characteristics of automotive lithium batteries and the transmission behavior of lithium ions in the process of charge-discharge cycle have been studied, which provides important data support for the improvement of lithium battery performance; and the atmospheric neutron spectrometer has been operated to accelerate the simulation of the neutron irradiation environment generated by cosmic rays hitting the atmosphereIt provides an important means to solve the problem of failure of electronic components in the atmosphere and on the ground, and provides a research platform for aircraft airworthiness demonstration and aircraft safety.
The Spallation Neutron Source actively promotes the transformation of relevant technological achievements. Boron neutron targeted tumor therapy is a new binary cell-level precision therapy technology for cancer, which is developed by using the technology developed by the China Spallation Neutron Source. As the first project to promote the industrialization of spallation neutron source technology, the clinical equipment has been installed and debugged in Dongguan People's Hospital, and clinical trials will begin soon.
The second phase of the China Spallation Neutron Source project was officially launched in January 2024. After the completion of the second phase of the project, the number of spectrometers of the China Spallation Neutron Source will be increased to 20, and the power of the accelerator target beam will be increased from 100 kilowatts in the first phase to 500 kilowatts. After the completion of the new spectrometer and experimental terminal, the equipment research capacity of the China Spallation Neutron Source will be greatly improved, the experimental accuracy and speed will be significantly improved, and it will be able to measure smaller samples and study faster dynamic processes, providing a more advanced research platform for cutting-edge scientific research, major national needs and national economic development.
The completion of the China Spallation Neutron Source coincides with the good era of the development of large scientific facilities, shouldering the important task of developing the research and application of neutron scattering in China, providing an important engine for the country's innovation and development, and contributing to the realization of high-level scientific and technological self-reliance and self-reliance.