This article is a review of nuclear physics and nuclear applications, selected from "China's Discipline Development Strategy and Physics in the Next 10 Years". The series "China's Discipline Development Strategy in the Next 10 Years" is the result of the "Research on Discipline Development Strategy" of the National Natural Science Foundation of China and the Faculty of Chinese Academy of Sciences, published in 2012. This article is a summary of the development trend of nuclear physics and nuclear technology in that year, and can also be used as a comprehensive science introduction. We can see that in just a decade, many aspects have changed dramatically, but there are still many outstanding issues.
Written by 丨 Strategic Research Group
First, the laws and characteristics of development
Nuclear physics is a branch of physics that focuses on the study of strong interactions, but also involves weak interactions and electromagnetic interactions. Humans' understanding of strong interactions is far less than that of electrically weak interactions. For example, we are not well aware of the basic nuclear power. Although quantum chromodynamics has been widely accepted as a fundamental theory of strong interactions and has achieved great success in the perturbation region, non-perturbative physics such as quark confinement remains an unsolved fundamental physical problem. The goal of nuclear physics research is to explore the structure and state of matter controlled by strong interactions.
Schematic diagram of the atomic structure
The discipline of nuclear physics originated from an accidental experimental discovery. In 1896, when Becquerel was exploring the problems related to X-rays, which was an international hot topic in physics at the time, he unexpectedly found that uranium emitted an unknown ray. Through the study of this new radioactivity, the Curies discovered two new chemical elements, polonium and radium; Rutherford discovered different kinds of radioactivity and used natural alpha rays and the scattering of atoms to show that atoms have a core, that is, the presence of atomic nuclei.
With the further discovery of neutrons, it is clearly known that the nucleus is composed of protons and neutrons, and the basic research of nuclear physics has entered a period of great development, after which two new forms of interaction, strong interaction and weak interaction, have been discovered. With the discovery of nuclear fission and the need for war and the use of nuclear energy, nuclear physics has received the attention of some governments, promoted the development of basic research in nuclear physics, and a large number of accelerators have been built. Nuclear physicists synthesize new chemical elements and new nuclides through accelerators, and obtain a large amount of nuclear data through experiments, thus establishing and improving some basic nuclear models, such as droplet models, shell models, collective models and nuclear reaction models of atomic nuclei.
In turn, theoretical predictions further promote the development of experiments, which brings about the interaction of experimental research and theoretical research. The study of nuclear reactions and decay has also made it clear that the energy of the sun comes from nuclear fusion reactions, and the formation mechanism of some chemical elements and heavy atomic nuclei in the universe has been known, and the study of radioactivity has enabled scientists to correctly estimate the age of the earth. Therefore, the discipline of nuclear physics is an important branch of physics, which has an important role in promoting the development of other fields of natural science.
Artificial elements
From the perspective of energy or material composition units, nuclear physics research is divided into low-energy and medium- and high-energy nuclear physics, corresponding to the nucleon, meson and quark levels of matter, respectively. Nuclear physics can be divided into two parts: nuclear structure and nuclear reaction. The former discusses the structure of atomic nuclei, while the latter emphasizes the dynamics of particle collisions. Since the 1960s and 1970s, based on the understanding of the deep hierarchy of matter and the vacuum state of QCD, people have begun to link microscopic dynamics research with macroscopic study of matter state, and explore the properties of QCD and the symmetrical properties of strong interaction under high temperature and high density conditions.
A distinctive feature of nuclear physics research is the critical role of large nuclear experimental devices. In recent years, many large nuclear physics experimental devices have been built and put into operation. For example, in the field of low- and medium-energy nuclear physics, there are HISFL-CSR in China and the radioactive beam device BRIFII of the Chinese Academy of Atomic Energy Sciences, the RBF/RIKEN radioion beam factory in Japan, and the FRIB/MSU of the Rare Isotope Beam Device in the United States. In the field of nuclear physics, there are the American electron beam device CEBAF and its improved and upgraded version in recent years, Germany's DESY uses proton beam HERA, CERN uses electron beam COMPASS, Germany's Ulich Research Center uses proton beam COSY, and Japan has JPARC. In the field of high-energy nuclear physics, there are rhic in the United States, the German antiproton and ion research plant FAIR/GSI, and cernion research at CERN LHC-ALICE. The completion and commissioning of these new devices has brought new opportunities for nuclear physics research.
Lanzhou heavy ion accelerator cooling storage loop HIRFL-CSR
Another feature of nuclear physics is that the object of study is a microscopic multiparticle system controlled by strong interaction dynamics, which leads to the close connection between nuclear physics research and the two difficult problems of current physics.
First, the law of low-energy strong interaction. Although QCD is widely accepted as a strong interaction theory and has achieved great success with perturbation theory at the high energy limit, how to use it to describe the interaction between low-energy hadrons is still an unsolved problem.
The second is multi-particle dynamics. For monomer or two-body problems, if the known interaction form can be treated with classical mechanics or quantum mechanics, and for systems with infinite number of particles, statistical mechanics can be used to describe it. But the nucleus is a multiparticle system in between, and it is impossible to deal with it rigorously by force or statistical methods. Given the small spatio-temporal scale, boundary effects and non-equilibrium effects of the microscopic system, the problem is further complicated.
These two dilemmas, on the one hand, make the study of nuclear physics face a complex microscopic system, and on the other hand, nuclear physics is always one of the frontiers of physics and even the entire science of matter.
Multiparticle system
Nuclear technology is based on the applied disciplines of nuclear effects, nuclear radiation and nuclear devices, and can be divided into two categories according to technical means: one is nuclear technology based on nuclear devices (accelerators, reactors, etc.) and the other is nuclear technology based on radionuclides. Traditional nuclear technologies include accelerator technology, nuclear detection technology, irradiation technology, ion beam analysis technology, X-ray analysis technology Neutron activation analysis technology, neutron scattering technology, radiolabeling and tracer technology, nuclear imaging technology, radiation protection, etc.
Nuclear technology has a wide range of applications, in the energy, medicine, materials, life, environment, geology and archaeology, agriculture, national defense, security and other fields have a very important application of nuclear technology and applications involving national security and economic development, has a very important position, is a strategic high technology.
Magnetic resonance imaging for medical use
Second, the current situation and trend of development
01 Nuclear physics
At present, the international nuclear physics community generally believes that the current hot spots and opportunities for nuclear physics research include the following four aspects: nuclear structure under extreme conditions, dynamics of intranuclear quarks, relativistic heavy ion collisions and quark gluon plasma, and nuclear astrophysics. In general, the current trend of nuclear physics research is towards extreme conditions (high energy, high temperature, high density, high spin, far from the stable line, superheavy nucleus, etc.) and the combination of particle physics and astrophysics.
(1) Nuclear structure under extreme conditions
Before the 1980s, nuclear physicists studied in detail the properties of hundreds of nuclides near the stability line of the β, establishing atomic core shell models, collective models, group models, and some nuclear reaction models. Since then, much progress has been made in the development of radioactive beam devices and detectors, making it possible to experimentally synthesize and study nuclei that are far from the stabilization line.
For nearly 20 years, radiological nuclear beam physics has constituted a new field of nuclear physics, studying the properties of thousands of unstable nuclei that have been or will be produced on new large scientific devices. Although the existing research is still preliminary, it has led to great developments in various branches of nuclear physics.
(1) Nuclear structure: Challenge the proposed theoretical model of nuclear structure based on the core near the stability line, such as shell model and collective model, and at the same time it is possible to discover new ways of motion in the nucleus, and now it has been discovered that strange light nuclei have halo structures, group structures, new magic numbers, nonlinear multi-nucleon associations and other novel quantum multibody phenomena.
(2) Nuclear decay: Thousands of unstable away from the β stable line peculiar nuclei will provide a very rich variety of nuclear decay, from which new decay patterns can be found, such as proton radioactivity (single proton or biproton) nodule radiation, β-slow neutrons, β-slow protons, β-brady fission, etc.
(3) Nuclear reactions: Due to the great increase in the types of nuclides, many new nuclear reaction systems will appear, and these new nuclear reaction systems will lead to the discovery of new reaction types and reaction mechanisms, and new nuclear reaction mechanisms and effects such as abnormal cross-sectional increase, multi-reactor coupling, group rupture and multi-step transfer have been observed.
(4) Application: The development and utilization of nuclear energy today is based on the knowledge of the structure, decay and reaction of stable nuclei in the past, and now the study of the structure, decay and reaction of the strange nuclei far away from the β stabilization line will likely provide new knowledge of nuclear chain reactions, so that people will have new ideas for the development and utilization of nuclear energy. The study of radioactive nuclear beam physics is a pioneering research work on a large number of unknown atomic nuclei, which will synthesize many new atomic nuclei and study their various properties, which may change people's traditional understanding of atomic nuclei and discover completely novel nuclear phenomena and new physical laws.
Schematic diagram of the structural composition of atoms
α decay of uranium-238
Schematic diagram of two nuclear reactions
(2) Dynamics of intranuclear quarks
How do quarks and gluons make up nucleons? The nucleon is the simplest system that embodies the three color synthesis colorlessness of the strong interaction theory QCD and its non-Abelle properties, but at present we cannot quantitatively describe the internal quark-gluon structure of the nucleon using the QCD theory, and even what the effective degrees of freedom inside the nucleon are is not clear.
Classical images of nucleon structures consist of three quarks, but there are growing experimental indications that the nucleon contains a significant polyquark component inside, and that the gluon component also contributes to problems such as nucleon spin polarization. Many of the nucleon excited states predicted by various theoretical models have not been found, and the search for "missing" baryon excited states is a hot spot in the current international high-energy nuclear physics research.
In addition, how to describe the interaction between nucleons at the quark level, whether there are polyquark states and dual substates, and how the quark gluon structure of the nucleus kernel differs from the free nucleons are all important for understanding the strong interactions. Due to the non-perturbative feature. For example, quark gluon confinement and spontaneous disruption of hand sign symmetry make it difficult for QCD to describe low-energy-strong interactions. Currently, only some phenomena can be described using lattice QCD and effective field theory, as well as QCD large NC unfolding. How to study the nature of strong interactions directly from QCD theory is a major challenge for physics.
The hadron in the quark model, inside are the quarks
The phenomenon of three injections in the high-energy positron-negative electron collision experiment shows the presence of gluons, and it is gluons that connect each pellet
(3) Relativistic heavy ion collision with quark gluon plasma
QCD is the basic theory of strong interaction. Despite the great success of perturbation QCD, non-perturbation phenomena such as low-energy confinement and vacuum symmetry breaking have always been difficult problems in particle physics and nuclear physics. In 1974, Li Zhengdao proposed that the symmetry of the physical vacuum was restored by generating high energy density in a large volume through the collision of relativistic heavy ions, and the quark gluon was released from confinement and moved in a space-time range larger than the scale of hadrons. The expansion of the space in motion of quark gluons means that a phase transition from hadronous matter to quark matter occurs, producing a quark substance called a quark gluon plasma (QGP).
Another important QCD phase transition is the recovery of spontaneously broken hand symmetry in a vacuum at finite temperature density. According to modern cosmology, high-temperature quark matter may be the state of the universe in the instant after the Big Bang, and exploring and studying high-temperature quark matter can deepen our understanding of the early universe. For dense stars currently present in the universe, their interiors are likely to be in a high-density quark or hadron material state.
On Earth, relativistic heavy ion collisions are the only possible means of producing new forms of matter in the laboratory. There is clear evidence that new forms of matter may have been produced in experiments. Since the high-temperature and high-density QGP can only be the intermediate state of heavy ion collision, the low-temperature and low-density end state is still the lepton hadron state, and whether the collision system has experienced the QGP state is inferred by the terminal state distribution. The final distribution with QGP characteristics is called the signal that produces the QGP. Since the QCD phase transition itself is in a strong coupling region, perturbation theory cannot be used, and the current theoretical tools for studying phase transitions are mainly QCD calculations at lattice points and effective models with QCD symmetry. How to determine the signal of the QCD phase transition and study the properties of strongly coupled quark matter is the central problem of the current relativistic heavy ion collision and quark matter research.
At very high temperatures and densities, there are free, untethered quark-gluon plasmas
(4) Nuclear astrophysics
Nuclear astrophysics is an interdisciplinary discipline formed by combining the study of nuclear physics in the microscopic world with the study of astrophysics of the macroscopic world, which applies the knowledge and laws of nuclear physics to explain the energy generated by nuclear processes in stars and their influence on the structure and evolution of stars.
The nuclear process is the only mechanism by which stars resist their main energy source of gravitational contraction and the synthesis of various nuclides in the universe, and play an extremely important role in the evolution of the universe and celestial bodies after the Big Bang. The nuclear processes in the stable nuclear combustion phase of a star are essentially nuclear reactions that develop along a stable path. In the high-temperature environments of explosive celestial events such as novae, supernovae, and X-ray explosions, nuclear reactions occur in exactly different ways than stable nuclei in the nuclide table. In today's world of highly radioactive nuclear beams, it is possible to reproduce the processes of these reactions in the laboratory.
Currently, data are available for nuclides that are not far from the stabilization line, and for nuclides that are far from the stabilization line, especially near the reaction path, there are few or no data. The reaction path itself is correlated with the physical environment of the explosive celestial event (temperature, density, chemical composition, etc.), and may approach proton and neutron drips when temperatures and densities are high. Nuclear processes in explosive celestial events are at the forefront of current nuclear astrophysics, and measuring related data is challenging research.
Schematic of the Big Bang
02 Nuclear technology
Nuclear imaging technology was the first nuclear technique to be applied, and the application of nuclear imaging technology began soon after Röntgen discovered X-rays. Its application in human health and medical diagnosis is an example of the successful application of nuclear imaging techniques.
In the past 20 years, nuclear medicine and molecular imaging supported by nuclear imaging technology have developed particularly rapidly and have become an indispensable means of medical clinical diagnosis. Nuclear medicine functional imaging can find lesions earlier than structural imaging, can truly reflect the occurrence and development process of diseases, and has become an effective and important indicator for disease judgment and treatment effect evaluation in cerebrovascular, cardiovascular disease and tumor diagnosis. Major nuclear scientific research institutions around the world have used the foundation of nuclear science to carry out related technical research, such as CERN, many national laboratories in the United States DOE, Japan Riken Institute of Physics and Chemistry (RIKEN), Japan National Institute of Radiological Science (NIRS), etc., are strengthening imaging technology research and applied research in neurological, cognitive, oncology and other aspects. The National Institutes of Biomedical Imaging and Bioengineering (NBIB) was established by the National Institutes of Health (NIH) in 2001 with a mission to focus and coordinate the application of engineering and imaging sciences to basic research in biology, medicine, and other fields.
Positron emission computed tomography, the most advanced medical imaging technology for functional imaging of the human body
Radiation therapy is another important application of nuclear technology in human health. Malignant tumors are common diseases and diseases that are extremely harmful to human health, and have been plaguing the medical community in countries around the world, ranking second in various causes of death. At present, surgery, radiation therapy and chemotherapy are the three major means of tumor treatment. According to statistics, the five-year survival rate of cancer patients treated by different methods has reached more than 45%, of which 40% are patients who have undergone radiation therapy.
In recent years, the application of various advanced technologies in the field of accelerator-based radiation therapy (intensity-modulated therapy, image-guided therapy, proton therapy, heavy ion therapy, etc.) has significantly improved the cure rate and effective control rate of cancer radiation therapy, radiation therapy has enabled some early local tumors to be cured, and radiation therapy has important significance for the preservation of organs and functions at the site of cancer. Especially in recent years, the development of electron linear accelerators in the X-band and C-band has further miniaturized, produced some new radiotherapy equipment, and gradually industrialized. In view of the unique advantages of protons and heavy ions in radiation therapy, countries have successively carried out research on proton and heavy ion cyclotrons and synchrotrons specifically for radiation therapy. It is foreseeable that radiation therapy will still occupy an important position in the treatment of tumors for a long time to come.
Radiotherapy instruments for medical use
The use of nuclear energy is one of the most important aspects of the application of nuclear technology, involving almost all the technical methods of nuclear technology, and is the best example of the integrated application of nuclear technology. The level of a country's nuclear energy utilization is often a comprehensive embodiment of its nuclear technology and application level. The safe, clean and efficient use of nuclear energy is a key area in which the world's major powers are competing to invest heavily in research and development.
Daya Bay Nuclear Power Plant
Nuclear technology has important uses in terms of national security. Toxic and harmful substances and explosives are one of the important root causes of endangering national security and social stability, the development of its detection and diagnostic technology in various countries around the world has been widely valued, the current development of technical means are basically based on nuclear technology, including ion mobility spectrometer (MS) neutron scattering, coherent X-ray, nuclear quadrupolar resonance, etc., of which MS technology has been the most widely developed and applied because of its fast, efficient, sensitive and small advantages. In addition, container inspection technology based on accelerator X-ray sources has played an important role in detecting smuggled and prohibited items at customs ports, resulting in significant social and economic benefits.
Ionic pyrotechnic alarm
Nuclear technology has played an important role in archaeology and the study of artifacts. The application of nuclear technology has fundamentally changed the face of archaeology, making it gradually become the science of quantitative expression. Once nuclear technology is applied to archaeology, it constantly reveals the rich potential information of ancient remains, raises archaeological research to a new level, and fundamentally changes its research appearance, so in a sense, nuclear technology has a special significance for the development of archaeology. Nuclear analysis technology has played an irreplaceable role in the study of precious cultural relics because of its ability to non-destructively analyze.
The 114C decay process, using the radiation level of modern carbon fourteen as the standard compared with carbon fourteen in the measured specimen, deduces the age when carbon fourteen of the carbon-containing substance died or stopped exchanging
Irradiation technology is one of the traditional fields of nuclear technology applications, which has been widely used in basic research, application development and industrial development. Radiation technology mainly uses the effect of radiation to solve special technical problems. In the 1950s, British scientists discovered that polyethylene cables were crosslinked after being irradiated in nuclear reactors, and the radiation effect and radiation processing of polymer materials were rapidly developed. In 1962, American scientists used pulsed electron accelerators and time-resolved techniques to observe the hydrated electrons produced by radiation, which rapidly promoted the development of radiation chemistry and radiation technology.
Radiation technology has played an important role in the fields of polymer materials, high-performance fibers, food sterilization and preservation, disinfection of medical supplies, plant and microbial breeding, environmental governance, nanomaterials and even cultural relics protection, energy and other fields by using high-energy rays to irradiate substances. After decades of development, the irradiation technology method has been relatively mature, and the current focus is mainly on the key technical issues in the promotion and application and the study of radiation biological effects, etc., and still shows a rapid development trend in the world. In addition, the intersection of radiation chemistry and other disciplines also has a broad future.
Irradiated polyethylene cable
As an extension of accelerator-based nuclear technology, synchrotron radiation technology has been developed extremely rapidly in the international community in the past 20 years. Synchrotron radiation light sources are devices that emit electromagnetic radiation when high-energy electrons or positrons are accelerated. Synchrotron radiation light source has the characteristics of wide continuous spectrum, high brightness, high collimation, high polarization, pulse time structure and high purity that conventional light sources do not have. Its application provides a powerful experimental technology means and comprehensive research platform for the basic research of many disciplines, the development of science and technology and its application, and greatly promotes the rapid development of multiple disciplines (such as structural biology, molecular environmental science, etc.). Its construction and operation have an important role in promoting accelerator technology and other high technologies.
At present, international research in this field is characterized by two aspects. On the one hand, the study of advanced technologies and new methods of synchrotron radiation. High spatial resolution experimental techniques and methods: The typical spatial resolution scale is promoted from micrometers to nanospeakers, and the typical time-resolving scale is advanced from microseconds (us) to nanoseconds (ns) to nanoseconds (ps). High energy resolution experimental technique, typical energy resolution from eV to meV. The development of analytical theoretical methods related to high-momentum resolution experimental techniques, high-sensitivity experimental techniques, and experimental techniques and methods that utilize synchronous photopolarization characteristics has attracted increasing attention.
The development of these advanced technologies and methods has greatly expanded the scope and depth of synchrotron radiation applications, deepened the understanding of the various hierarchies and properties of matter, enriched and developed the knowledge and theory of non-steady-state structures and kinetic processes, and made them widely used in physics, chemistry, life science, materials science, environmental science, energy science, geoscience, medical microelectronics and micromachining.
On the other hand, the wide application of synchrotron radiation in the above fields, especially in the life sciences, materials science, energy science, environmental science, medicine and other disciplines with important practical prospects, is expected to have a significant impact on human health and sustainable socio-economic development. At present, the third generation of synchrotron radiation light sources that have been operated internationally can average thousands of users from various disciplines to carry out various topic research projects every year, which is a natural interdisciplinary research platform and has attracted the attention of the scientific and technological community around the world. So far, more than 60 synchrotron radiation devices have been operated and under construction around the world, providing an experimental research platform for tens of thousands of research topics.
Shanghai synchrotron radiation light source
The high-intensity neutron source technology (spallation neutron source) based on the development of particle accelerator technology has pushed neutron technology and application to a new height, greatly expanding the breadth and depth of the application of conventional neutron scattering technology and becoming an important means of research and technological development in many disciplines. In addition, many universities and research institutions in the world are also carrying out research on accelerator-based small neutron sources. For example, Indiana University in the United States based on proton accelerator low energy neutron source (LENS), Hokkaido University in Japan based on electron linear accelerator neutron source, etc., in the neutron and proton science, to carry out innovative research work and neutron proton application innovative talents training.
Diagram of the Neutron Source Model for Spallation in the United Kingdom
This article is reprinted with permission from the WeChat public account "School of Physics, Jilin University", and the original article is excerpted from the section of "Nuclear Physics and Nuclear Technology" of "Development Strategy and Physics of Chinese Disciplines in the Next 10 Years".