China's spalling-neutron sources hit the target successfully for the first time. What can a "super microscope" see
Time：2018-11-11 17:08:57 View：
A few days ago, China's spalling-neutron source (CSNS), a national science project located in dongguan, guangdong province, successfully hit a target for the first time and acquired the neutron beam, marking the successful completion of CSNS 'main project and entering the trial operation stage. What is the spallation neutron source in China? What does it look like? What's the use? Is it safe? Our reporter went to the scene for you to reveal one by one.
An aerial view of China's spalling neutron source park. Chinese spallation neutron source supply map
Q: what is it?
Like a "super microscope", it can study the microstructure of matter
"When a neutron beam is incident on the study sample, it interacts with its nucleus or magnetic moment to produce scattering. By measuring the changes of scattered neutron energy and momentum, we can study the microstructure and motion of various substances on the atomic and molecular scales, and tell people the position and motion state of atoms and molecules. This is called neutron scattering technique. China spallation neutron source engineering general director, engineering manager, cas academician Chen hesheng said.
In 1932, when the British physicist Chadwick discovered the neutron, people began to realize that the nucleus was made up of positively charged protons and uncharged neutrons. The discovery and application of neutrons is one of the most important scientific and technological achievements of the 20th century. Because the neutron has no charge, with a magnetic moment, and penetrability is strong, can distinguish the lighter elements, isotope and neighboring elements, non-destructive, these features makes neutron scattering research material structure and dynamics properties, one of the ideal probe and X-ray, is a multidisciplinary research in detecting material microstructure and powerful means of atomic motion.
"Let's say we have an invisible net in front of us," Chen explained. "we keep throwing marbles. If the trajectory of these marbles is recorded, the shape of the net can be estimated. If the marbles are thick enough, thick enough and strong enough, they can be accurately depicted or even inferred from the material.
However, the study of neutron scattering requires the use of neutron as a probe and an appropriate neutron source. How to obtain a neutron source that produces a high flux of neutrons has always been the goal of scientists.
High flux neutron sources include reactor neutron source and spallation neutron source. Nuclear reactor is a stable and continuous neutron source, which plays an important role in the research of neutron. But the reactor's neutron flux was saturated in the 1960s and 1970s because of the limits of its cooling technology. With the progress of science and technology, the corresponding research systems, such as thin films, nanoclusters, biomacromolecules and proteins, have a larger scale distribution, and it is more difficult to obtain samples with a quantity of grams. Therefore, the fast and high resolution neutron scattering measurement of small samples urgently needs a new generation of neutron sources with higher flux and wider band.
"It is bombarding heavy metal targets with high-energy protons from large accelerators, causing the spallation of metal atoms and releasing large amounts of neutrons. These neutrons form a very strong neutron beam. After neutron-slowing (the phenomenon of neutron slowing down due to the neutron energy reduction caused by the collision of the neutron with the nucleus of the medium), they scatter with the sample and are finally received by the neutron scattering spectrometer. Based on these neutron scattering data, our researchers have analyzed the microscopic characteristics of the object under observation. In layman's terms, a spalling-neutron source is like a 'super microscope' that studies the microstructure of things like DNA, crystalline materials, polymers, etc. "Said Chen.
Ask: grow what appearance?
It's huge, built between 13 and 18 meters underground
Because of these unique properties of spallation neutron sources and the increasingly stringent safety assessment requirements of the international community, spallation neutron sources are widely used in developed countries for neutron scattering studies. At present, the countries that are running pulse-type spalling neutron sources in the world mainly include Britain, America and Japan. China's spallation neutron source will become the first spallation neutron source in developing countries, ranking among the world's four major pulsed spallation neutron sources, thus greatly improving the level of basic research and high technology in China.
Although the neutron is so small, the spallation neutron source that produces the strong neutron beam is an unusually large device, a whole of various high, fine and pointed equipment.
Reporters at the scene saw the CSNS tunnel device built in 13 meters to 18 meters deep underground. The main construction contents include 1 negative hydrogen ion linear accelerator with beam energy of 80 mev, 1 beam energy of 1.6 billion electron volt, 2 beam transport lines, 1 target station and 3 spectrometer, and corresponding supporting facilities and civil engineering.
"The number of subspectrometer in the first phase of CSNS project is three, and it can be up to 20 in the future," Chen said. At present, the beam power is 100 kilowatts, and there is room for further improvement of the beam power to 500 kilowatts and for upgrading the second target station.
The first three spectrometers are general powder diffraction instrument, multifunctional reflectometer and small Angle scattering instrument.
"General powder diffractometer is mainly used to study the crystal structure and magnetic structure of substances; The multifunctional reflectometer studies the surface and interface structure of materials by analyzing reflected neutrons from samples. Small Angle scatterometer is used to detect the micro and mesoscopic (a system between macro and micro) structure of the material system at the scale of 1-100 nanometers. "Said Chen.
Three ask: what use?
It can make high-speed rail and aircraft safer and more comfortable, and can be used in the research of radiation therapy for tumors
The spallation neutron source can generate intense pulsed neutrons and detect the position and motion of sample nuclei by measuring the scattering reaction process of the neutron beam in the sample. Therefore, it has a broad application prospect in materials science and technology, life science, physics, chemical engineering, resources and environment, new energy and other fields.
Chen hesheng gives an example. "In June 1998, a German intercity express derailed and turned out to be the result of aging wheels. The wheels were tested on a UK spalling neutron source and found to have internal cracks.
In fact, there is stress in the wheels and rails of high-speed rail, in the turbines and wings of aircraft, which determine the service life and safety of high-speed rail and aircraft. But the stress is invisible and undetectable, and the study of it is the key to avoiding disaster. Scientists can now measure and study the residual stress of wheel rails and wings on spalling neutron sources, optimize machining processes, and make high-speed rail and aircraft safer and more comfortable.
"" spalling-neutron source technology also plays an irreplaceable role in biological, life and medical research fields, and complements the synchrotron radiation light source, becoming one of the most important platforms for basic scientific research and new material research and development," "Chen said. For example, protons and neutrons from spallous neutron sources can be used in radiation therapy of tumors and have been used in many developed countries. In addition, in the development and utilization of new type of clean energy combustible ice, the neutron diffraction technology of spalling-neutron source under high pressure can be used to study the formation mechanism and stability conditions of the combustible gas methane hydrate, and the research results will provide scientific basis for the safe and efficient exploitation and utilization of combustible ice.
The construction of CSNS device will also greatly strengthen the international communication and cooperation in the field of neutron scattering science and application in China, and provide a good opportunity for China's neutron scattering technology and application to occupy a position in the international frontier field.
"In the construction of CSNS, the construction of proton accelerators, target stations and neutron spectrometer involves a large number of high technologies of strategic significance, and these technical difficulties need to be solved by China's top scientific research forces. Therefore, the construction of this project will attract a large number of world-class scientists to carry out scientific research activities, and when completed, it will attract more than 600 experts and scholars from home and abroad to gather in dongguan for research. Sun mu, party secretary of the institute of physics, Chinese academy of sciences.
Q: is it safe?
Living nearby for a year receives the radiation equivalent of just one long flight
What about the safety of such a large scientific device? Will it pollute the surrounding environment?
"CSNS is based on a new generation of accelerator. It does not need nuclear materials, and its power comes from electricity. We have calculated that a person living near a spallous neutron source for one year would be exposed to the same amount of radiation as a long-haul flight.
According to the introduction, CSNS near the establishment of monitoring station, monitoring radiation at any time. The environmental impact report of spallation neutron source project also puts forward the accident emergency plan. As the spallation neutron source is a radiation device, the main radiation generated by the neutron source will disappear as soon as the power is shut down.
In addition, the spallation neutron source is completely different from the reactor type nuclear device. There is no need for nuclear material and there is no chain nuclear reaction. When the accelerator is running, a small number of particles are lost to produce secondary particles, such as the radioactive powder ray, gamma ray and neutron.
"The radioactive material, which is five to six orders of magnitude lower than the reactor's neutron source, has a much smaller environmental impact and will be stored in a state-designated waste repository." China's spalling neutron source engineering deputy manager Chen yuanbo said.
"As long as the accelerator is shut down, the main source of radiation causing the environmental impact is gone, which can be said to be as safe and reliable as a tap. Accelerators are automatically triggered and stopped by electronic devices and can be turned off in milliseconds if they fail. In the event of natural disasters such as earthquakes, the spallation neutron source machine will stop working and the radiation field will immediately disappear. After repeated studies, the spallation neutron source is a relatively clean radiation device. "Said Chen.
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