How does a Particle Accelerator Work?

The full name of particle accelerator is charged particle accelerator, which is a special electromagnetic and high vacuum device that enables charged particles to be controlled by magnetic field forces and accelerated by electric field forces in high vacuum fields. It is a modern equipment that artificially provides various high-energy particle beams or radiations ^[1] .

Particle accelerator

particle

Since the 1980s, China has successively built four high-energy physics research facilities-

The structure of a particle accelerator generally includes 3 main parts:

There are many types of accelerators. So far, no fewer than dozens of them have been built or have been developed in the world. Some of them have been eliminated, and some are still immature. There are more than ten types that are widely adopted and shaped. They have different characteristics and can be classified according to different principles. ^[1]

Particles can be operated in the following modes: straight line, gyration, spiral, and automatic stabilization mechanism.

Accelerating Charge with Linear Accelerator

Beijing Electron Collider

The Beijing Electron-Positron Collider is a high-energy physics experimental device that can accelerate the positive and negative electron beams in the same ring in opposite directions and collide with each other at a designated location. due to

The research on the structure of matter under the condition of high-energy accelerator is essentially related to the relative change (transformation) of the energy state between natural energy groups (or energy clusters and energy ions) in the natural state.

From the perspective of arc theory, weak interactions can be obtained under conditions that use high-energy accelerators and other methods to bombard arc-like substructures (atoms): 1. Symmetry theory (universal symmetry theory) 2. Asymmetry theory , Obtained under special conditions. If you bombard energetics (archisons, subatomic structures), you get strong interactions: asymptotic freedom theory, etc.

why?

Both of these effects occur at the energy state level rather than at the material state level; the relationship between genus energy clusters and energy clusters.

Weak interaction: When any external energy group bombards the arc-like substructure, and enters the arc-like subordinate (from energy to energy) along the time axis, the energy is added

During the 20 years from the 1930s to the second half of the 1950s, the energy of the accelerator increased by hundreds to thousands of times. This is because

The application of electron beams or X-rays produced by accelerators for irradiation processing has become an important means and process of production in chemical, electric power, food, environmental protection and other industries, and is a new processing technology. It is widely used in polymer cross-linking modification, coating curing, polyethylene foaming, heat-shrinkable materials, semiconductor modification, wood-plastic composite material preparation, food sterilization and preservation, flue gas desulfurization and denitration, and other processing processes. .

The products produced by irradiation have many excellent characteristics, such as: after irradiation of 105Gy dose of irradiated cross-linked polyethylene cable, its electrical properties and thermal properties have been greatly improved, and the temperature before use is 60 ~ 70 , The long-term use temperature can reach above 120 after irradiation. There are more than 200 production lines using accelerators in China for irradiation processing.

Particle accelerator nondestructive testing

Non-destructive testing is to detect the internal conditions of materials, products or components without damaging and damaging them, and to determine whether there are defects inside. There are many modern non-destructive testing methods, such as: ultrasonic flaw detection method, eddy current flaw detection method, fluorescent flaw detection method and ray detection method. The radiographic inspection method can inspect both the surface of the workpiece and the defects inside the workpiece. The device can use gamma rays produced by the radioisotope Co60, low-energy X-rays produced by X-ray machines, and high-energy X-rays produced by electron accelerators. Especially the flaw detection accelerator has high penetration ability and sensitivity. It is used as a final inspection method or other verification methods for verification and in quality control, in large-scale cast and forged weldments, large pressure vessels, reactor pressure shells, and rocket solid fuels. It is widely used in defect inspection of workpieces. This flaw detection accelerator is based on an electronic linear accelerator.

The methods of radiographic inspection can be divided into three types according to the different methods of receiving and processing the rays transmitted through the workpiece:

a. Radiography

This method is similar to the X-ray film taken during our physical examination. The radiographic receiver is X-ray film. When detecting a flaw, place the film box containing the X-ray film against the back of the workpiece to be inspected. After irradiating the workpiece with X-rays, the film is sensitized through the rays of the workpiece, and the real situation inside the workpiece is reflected on the latex of the film After processing the photosensitive film, you can clearly understand whether there are defects in the workpiece and the type, location, shape and size of the defects.

b, radiation imaging

The radiation receiver of this method is an array detector or a fluorescence-sensitized screen. The former is a large container inspection product jointly developed and produced by Tsinghua University and Tsinghua Tongfang. The latter is an X-ray security inspection system for luggage and parcels at airports, railways, and non-destructive inspection in industry. This method, coupled with an image processing system, can display the real situation inside the item online in real time.

c. Industrial CT

Similar to the principle of medical CT, CT technology is computer-assisted tomography. CT technology, which uses an accelerator as an X-ray source, is an advanced non-destructive testing method, which is mainly developed for the detection of large solid rocket engines and precision workpieces. Its density resolution can reach 0.1%, which is an order of magnitude higher than conventional radiation technology. It has important application value in defect detection, dimensional measurement, and assembly structure analysis of precision workpieces in the fields of aerospace, aviation, weapons, and automobile manufacturing.

Particle accelerator ion implantation

Accelerators can be used to implant ions of a certain energy into the surface layer of solid materials to obtain good physical, chemical and electrical properties. Semiconductor devices, metal material modification, and large-scale integrated circuit production all use ion implantation technology. China now has more than 100 ion implanters of various types. Among them, China has produced more than 140 ion implanters with an energy of 150KeV ~ 600KeV (1KeV = 1 × 103eV) and a current intensity of 0.5mA to more than ten mA.

1.2 Application of Low Energy Accelerator in Agriculture

The application of accelerators as nuclear technology application equipment in agriculture has been widely used in some countries in three main areas:

1) Irradiation breeding

The application of accelerators in radiation breeding is mainly to use high-energy electrons, X-rays, fast neutrons or protons generated by it to irradiate crop seeds, buds, embryos, or grain pollen, etc., to change the genetic characteristics of crops, so that they are optimized development of. Breeding breeds through radiation mutation has played a significant role in improving yield, improving quality, shortening growth period, and enhancing stress resistance. Potatoes, wheat, rice, cotton, soybeans and other crops after irradiation breeding can have the advantages of high yield, early maturity, short stalks and resistance to diseases and insect pests.

2) Irradiation preservation

Irradiation preservation is a new preservation technology developed after traditional preservation methods such as heat treatment, dehydration, refrigeration, and chemical processing. For example, irradiated potatoes, garlic, onions, etc. can inhibit their germination and extend the storage period; dried and fresh fruits, mushrooms, sausages, etc., can extend the supply period and shelf life.

3) Irradiation and sterilization

Chemical fumigation is widely used in pesticide and sterilization of agricultural products and foods. Due to the residual toxicity caused by the use of chemical fumigation methods such as methyl bromide and ethylene oxide, and damage to the atmospheric ozone layer, according to the Montreal Convention, it will be in the global scope by 2005. The use of methyl bromide is prohibited. Therefore, the use of accelerators for agricultural products, food and other irradiation to kill insects and sterilization has developed rapidly. The use of high-energy electrons or X-rays generated by the accelerator can kill parasites and pathogenic bacteria in agricultural products and food, which can not only reduce the loss of food due to spoilage and pests, but also improve the quality of food hygiene and added value.

Particle accelerator medical health

With the advancement of science and technology and the improvement of people's life and quality, people have put forward higher requirements for medical and health conditions. The application of accelerators in medical care has promoted the development of medicine and the extension of human life. At present, there are three main applications of accelerators in medical and health, namely radiation therapy, production of medical isotopes, and disinfection of medical devices, medical supplies and drugs.

1) Radiation therapy

Medical accelerators for malignant tumor radiotherapy (referred to as radiotherapy) are the largest and most mature technology in various application fields of accelerators in the world today.

Accelerators for radiotherapy have been developed from induction accelerators in the 1950s to medical electronic cyclotrons in the 1960s, and medical electronic linear accelerators gradually dominated in the 1970s. There are more than 3,000 medical linear accelerators in the world in hospitals around the world.

In addition to the use of electron beams and X-rays generated by accelerators for radiation therapy, accelerators can also be used for proton, neutron, heavy ion, and meson radiotherapy. These cancer treatment methods are still in the experimental stage. Significant effect. However, these accelerators have much higher energy, more complicated structures, and are much more expensive than electronic linear accelerators.

The use of electronic linear accelerator for stereotactic radiotherapy, commonly known as X-knife, is a new radiotherapy technology developed. Compared with conventional radiotherapy, this technique can protect 15% ~ 20% of normal tissues, and tumors can increase the dose by 20% ~ 40%, which can more effectively kill cancer cells and increase the efficacy of radiotherapy.

In the 1960s, hospitals in China were equipped with medical induction accelerators, and in the 1970s, medical electronic linear accelerators began to be installed in hospitals throughout China. As of early 2000, China has about 530 medical accelerators of various energies, including about 250 domestic medical accelerators and about 300 imported medical accelerators.

Particle accelerator isotope

Modern nuclear medicine widely uses radioisotopes to diagnose diseases and treat tumors. About 80 isotopes have been identified as clinical applications, of which 2/3 are produced by accelerators, especially neutron-deficient short-lived isotopes can only be produced by accelerators. These short-lived isotopes are mainly used in the following areas:

a. Positron and single photon emission computed tomographyPET and SPECT

PET is inhaled or pre-injected by the patient with a very short half-life of positron-emitting radionuclides. These detectors are used to detect positrons and photons emitted from annihilation from various angles by a circularly arranged detector. The computer-processed reconstruction An image of the cut tissue. These short-lived radionuclides are made by small cyclotrons. The shortest half-life nuclides, such as 15O, are only 123 seconds, which is usually several minutes to one hour. Therefore, such accelerators are generally equipped in hospitals using PET. Small cyclotrons that produce short-lived radionuclides for PET have attracted many accelerator manufacturers to develop them. There are dozens of small cyclotrons produced by several foreign accelerator manufacturers.

b. Image acquisition

Using radionuclide scintillation scanning or gamma photography to acquire images can diagnose tumors, examine human organs, study their physiological and biochemical functions and metabolic status, and obtain dynamic data. For example, 201Tl is used for myocardial examination, which is the most sensitive inspection method for early detection of coronary heart disease and localization of myocardial infarction. Most of these radionuclides are also produced by accelerators.

Particle accelerator irradiation disinfection

The use of accelerators to sterilize and sterilize medical instruments, disposable medical articles, vaccines, antibiotics, and proprietary Chinese medicines is a promising future for accelerators in medical and health applications. Similar to the insecticidal and sterilizing principles of accelerators in food, it can replace the applied high-temperature disinfection and chemical disinfection methods. However, the dose of radiation required for sterilization is greater than that required for insecticide.

A particle accelerator is a device that uses artificial methods to generate high-speed charged particles. Common particle accelerators in daily life include facilities such as cathode ray tubes and X-ray tubes for televisions. It is an important tool for exploring the nature, internal structure and interaction of atomic nuclei and particles. It also has important and extensive practical applications in industrial and agricultural production, medical health, science and technology. Since E. Rutherford bombarded nitrogen atoms with a-rays emitted by natural radioactive elements in 1919 for the first time to realize the artificial conversion of the elements, physicists have realized that in order to understand the nucleus, high-speed particles must be used to transform the nucleus. Particles provided by natural radioactivity have limited energy, only a few megaelectron volts (MeV). Although the energy of particles in natural cosmic rays is very high, the particle flow is extremely weak. For example, particles with an energy of 10 ^ 14 electron volts (eV) per hour On an area of 1 square meter, there is only one on average, and it cannot control the type, number, and energy of particles in cosmic rays, making it difficult to carry out research. Therefore, in order to carry out experimental research with expected goals, people have developed and constructed a variety of particle accelerators for decades, and their performance has been continuously improved. In life, televisions and X-ray facilities are small particle accelerators.

The application of particle accelerators has found most of the new transuranium elements and thousands of new artificial radionuclides synthesized, and has systematically studied the basic structure of nuclear nuclei and their changing laws, which has promoted the rapid development and maturity of nuclear physics. Build particle physics. In the past 20 years, the application of accelerators has far exceeded the fields of nuclear physics and particle physics, and has important applications in other scientific and technological fields such as materials science, surface physics, molecular biology, and photochemistry. Accelerators are widely used in the fields of industry, agriculture, and medicine for isotope production, tumor diagnosis and treatment, radiation disinfection, non-destructive testing, polymer irradiation polymerization, material irradiation modification, ion implantation, ion beam microanalysis, and space radiation simulation. And nuclear explosion simulation. Thousands of particle accelerators have been built so far around the world, a small part of which is used for basic research on atomic nucleus and particle physics, and they continue to develop in the direction of increasing energy and improving beam quality; most of the rest belong to the application of particle rays Technology-based "small" accelerators ^[1] .