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Neutrons in Nuclear Reactors: How Do They Promote Fission Reactions?
Neutron radiation is a form of ionizing radiation from free neutrons in nuclear reactions. It is produced during nuclear fission and nuclear fusion and subsequently reacts with the nuclei of other atoms to form new nuclides and may trigger more neutrons. sub-radiation. Neutrons themselves are uncharged and therefore have higher penetration capabilities than other types of radiation during propagation, making their application in nuclear power generation and related fields particularly important.
Source of neutrons
Neutrons can be released from nuclear fission, nuclear fusion, radioactive decay, and even the interaction of cosmic rays with the Earth's atmosphere. Among these sources, nuclear reactors and particle accelerators are common large-scale sources of neutrons.
One of the typical neutron sources is the free neutrons produced in the collision of barium gamma rays and beryllium nuclei.
Neutrons in fission
In nuclear reactors, neutrons are usually divided into slow (thermal) neutrons and fast neutrons. Thermal neutrons exhibit a Maxwell-Boltzmann distribution similar to gases in energy distribution, and can be easily captured by atomic nuclei, which is the main way to produce fission chain reactions. In order to maintain an effective fission chain reaction, the neutrons produced by fission must be captured by a fissionable nucleus, which then undergoes fission to release more neutrons.
In order to slow down fast neutrons to thermal neutrons, neutron moderators, such as graphite or light water, are often introduced into the reactor to increase the capture efficiency.
Climate Neutrons
Climate neutrons are produced by cosmic radiation at the Earth's surface and atmosphere and typically have higher energies than neutrons in nuclear reactors. These neutrons can convert into carbon-14 when they interact with nitrogen-14, a feature that is widely used in radiocarbon dating.
Applications of neutrons
Cold, hot and thermal neutron radiation is widely used in scattering and diffraction experiments to help evaluate the properties of materials in fields such as physical science, crystallography and biology. To treat cancer, boron neutron capture therapy also takes advantage of the highly penetrating and damaging nature of neutrons, aiming to attack tumor cells. In addition, neutrons can also be used to image industrial components, which is of great significance to industries such as nuclear energy, aerospace, and high-reliability explosives.
Ionization mechanism and characteristics of neutrons
Because neutrons are uncharged, their ionization mechanism is different from that of charged particles. When neutron absorption results in the emission of gamma rays, these gamma rays remove electrons from the atoms, causing indirect ionization. Neutron radiation is extremely penetrating and, in some cases, can even outperform gamma rays.
Health Hazards and Protection
The main health risk of neutron radiation comes from the activation of radioactive materials it can cause, which causes many materials to become radioactive, including human tissue. Neutrons are a dangerous type of radiation due to their high-energy properties. Under external radiation sources, protection measures mainly rely on radiation shielding materials, such as water or hydrogen-rich materials, to effectively block the effects of neutron radiation.
The impact of materials
High-energy neutrons can damage and degrade materials over time. As the material is bombarded with neutrons, shock reactions react with atomic nuclei, causing the formation of dislocations and defects. This process reduces the reliability and lifespan of materials, especially in nuclear reactor pressure vessels.
Conclusion
As the demand for nuclear energy utilization increases, research on neutrons continues to seek better protection measures and application technologies. We should think more deeply: What role and impact do these invisible forces play in our daily lives?
