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Neutrons in the Universe: How Do Cosmic Rays Produce These Mysterious Particles?
Neutron radiation, as a type of ionizing radiation, often appears in the form of free neutrons. These mysterious particles usually originate from the phenomena of nuclear fission or nuclear fusion, which release free neutrons in the reaction. These neutrons then react with the nuclei of other atoms to form new isotopes, which in turn may trigger further neutron radiation. Understanding the origins of these particles and their behavior is not only crucial for physicists, but also has far-reaching implications for research in fields such as biology and materials science.
The average lifetime of free neutrons is 887 seconds (14 minutes 47 seconds), indicating that their decay properties are quite special.
Sources of Neutrons
Neutrons can be released by nuclear fusion, nuclear fission, or other nuclear reactions such as radioactive decay, or by interactions with particles from cosmic rays. Large neutron sources are relatively rare and are usually found in large facilities such as nuclear reactors or particle accelerators. The discovery of neutron radiation came from the observation of an alpha particle colliding with a barium nucleus, which releases a neutron and transforms it into a carbon nucleus, becoming an important source of neutrons.
Neutrons in Nuclear Fission
In nuclear reactors, neutrons are generally classified as either slow (thermal) or fast neutrons, which are distinguished by their energy. The energy distribution of slow neutrons is similar to the Maxwell–Boltzmann distribution of gas, which makes them easily captured by atomic nuclei and thus become the main means of nuclear transformation of elements. In order to achieve an effective fission chain reaction, neutrons produced by nuclear fission must be captured by fissionable nuclei, which then undergo fission to release more neutrons.
In order to achieve adequate absorption, a neutron moderator is sometimes needed to slow the fast neutrons to thermal speed for effective absorption.
Neutrons from the Universe
Cosmically produced neutrons are generated in the Earth's atmosphere or on the surface by cosmic radiation, and these neutrons generally have higher energy levels than neutrons produced in reactors. When these neutrons interact with nitrogen-14 atoms, they convert it into carbon-14, which is widely used in radiocarbon dating.
Applications of Neutrons
Cold, hot and thermal neutron radiation is commonly used in scattering and diffraction experiments to evaluate the properties and structure of materials in crystallography, condensed matter physics, biology and materials science. Neutron radiation is also used in boron neutron capture therapy to fight cancer, making it an effective treatment due to its high penetration and damaging effect on cell structures.
Neutron ionization mechanism and characteristics
Neutron radiation is often called indirect ionizing radiation because it has no electrical charge and does not induce ionization in the same way. When neutrons interact with atoms, they may result in the release of gamma rays through neutron absorption, which in turn causes electrons to be removed from other atoms. Neutrons, because they have no electrical charge, are more penetrating than alpha or beta radiation. In some cases, its penetrating power is even greater than that of gamma radiation.
Health Hazards and Protection
In health physics, neutron radiation is a radiation hazard. Another more serious hazard caused by neutron radiation is neutron activation, which is the ability of neutron radiation to induce radioactivity in most substances, including human tissue. This process is triggered by neutron capture and often results in the release of radioactive material. It is one of the main causes of radioactive material released when a nuclear weapon is detonated.
Protection against neutron radiation relies on radiation shielding. Materials with high hydrogen content such as water or polyethylene are effective neutron shielding materials.
Influence on Materials
High-energy neutrons damage and degrade materials over time. When neutrons bombard materials, they create a collision cascade, which causes defects and dislocations within the material, leading to changes in the microstructure. In some cases, this could have important consequences for the life of a nuclear reactor, as such damage could cause materials to become brittle, which may eventually need to be replaced.
In summary, neutrons play a mysterious role in the universe. As we deepen our understanding of these particles, neutrons will continue to be an important topic of future research, both in scientific research and in applications that benefit human society. Are you ready to explore these mysterious cosmic rays?
