Neutron is a neutral particle belonging to the class of hadrons. Discovered in 1932 by the English physicist J. Chadwick. Together with protons, neutrons are part of atomic nuclei. The electric charge of the neutron is zero. This is confirmed by direct measurements of the charge from the deflection of the neutron beam in strong electric fields, which showed that (here is the elementary electric charge, i.e., the absolute value of the electron charge). Indirect data give an estimate. The neutron spin is 1/2. As a hadron with a half-integer spin, it belongs to the group of baryons (see Proton). Every baryon has an antiparticle; The antineutron was discovered in 1956 in experiments on the scattering of antiprotons by nuclei. The antineutron differs from the neutron in the sign of the baryon charge; a neutron, like a proton, has a baryon charge.
Like the proton and other hadrons, the neutron is not a true elementary particle: it consists of one m-quark with an electric charge and two -quarks with a charge - , interconnected by a gluon field (see Elementary particles, Quarks, Strong interactions).
Neutrons are stable only in stable atomic nuclei. A free neutron is an unstable particle that decays into a proton, an electron, and an electron antineutrino (see Beta decay):. The lifetime of a neutron is s, i.e., about 15 min. Neutrons exist in free form in matter even less due to strong absorption by their nuclei. Therefore, they arise in nature or are obtained in the laboratory only as a result of nuclear reactions.
According to the energy balance of various nuclear reactions, the value of the difference between the masses of a neutron and a proton is determined: MeV. By comparing it with the mass of the proton, we obtain the mass of the neutron: MeV; this corresponds to r, or , where is the mass of the electron.
The neutron participates in all kinds of fundamental interactions (see Unity of the Forces of Nature). Strong interactions bind neutrons and protons in atomic nuclei. An example of a weak interaction - neutron beta decay - has already been considered here. Does this neutral particle participate in electromagnetic interactions? The neutron has an internal structure, and in the case of general neutrality there are electric currents in it, leading, in particular, to the appearance of a magnetic moment in the neutron. In other words, in a magnetic field, a neutron behaves like a compass needle.
This is just one example of its electromagnetic interaction.
The search for the electric dipole moment of the neutron acquired great interest, for which the upper limit was obtained: . Here the scientists of the Leningrad Institute of Nuclear Physics of the Academy of Sciences of the USSR managed to perform the most effective experiments. Searches for the dipole moment of neutrons are important for understanding the mechanisms of violation of invariance with respect to time reversal in microprocesses (see parity).
Gravitational interactions of neutrons were observed directly from their incidence in the Earth's gravitational field.
Now a conditional classification of neutrons according to their kinetic energy has been adopted: slow neutrons eV, there are many varieties of them), fast neutrons (eV), high-energy eV). Very interesting properties have very slow neutrons (eV), called ultracold. It turned out that ultracold neutrons can be accumulated in "magnetic traps" and even their spins can be oriented there in a certain direction. Using magnetic fields of a special configuration, ultracold neutrons are isolated from absorbing walls and can "live" in a trap until they decay. This allows many subtle experiments to study the properties of neutrons.
Another method of storing ultracold neutrons is based on their wave properties. At low energy, the de Broglie wavelength (see Quantum Mechanics) is so large that neutrons are reflected from the nuclei of matter, just as light is reflected from a mirror. Such neutrons can simply be stored in a closed "bank". This idea was put forward by the Soviet physicist Ya. B. Zel'dovich in the late 1950s, and the first results were obtained in Dubna at the Joint Institute for Nuclear Research almost a decade later. Recently, Soviet scientists managed to build a vessel in which ultracold neutrons live until their natural decay.
Free neutrons are able to actively interact with atomic nuclei, causing nuclear reactions. As a result of the interaction of slow neutrons with matter, resonance effects, diffraction scattering in crystals, etc. can be observed. Due to these features, neutrons are widely used in nuclear physics and solid state physics. They play an important role in nuclear power engineering, in the production of transuranium elements and radioactive isotopes, and find practical applications in chemical analysis and geological exploration.
What is a neutron? This question most often arises among people who are not involved in nuclear physics, because the neutron in it is understood as an elementary particle that has no electric charge and has a mass that is 1838.4 times greater than the electronic one. Together with the proton, whose mass is slightly less than the mass of the neutron, it is the "brick" of the atomic nucleus. In elementary particle physics, the neutron and the proton are considered to be two different forms of one particle - the nucleon.
The neutron is present in the composition of the nuclei of atoms for each chemical element, the only exception is the hydrogen atom, the nucleus of which is one proton. What is a neutron, what structure does it have? Although it is called the elementary "brick" of the kernel, it still has its own internal structure. In particular, it belongs to the family of baryons and consists of three quarks, two of which are down-type quarks, and one is up-type. All quarks have a fractional electric charge: the top one is positively charged (+2/3 of the electron charge), and the bottom one is negatively charged (-1/3 of the electron charge). That is why the neutron does not have an electric charge, because it is simply compensated for by the quarks that make it up. However, the neutron's magnetic moment is not zero.
In the composition of the neutron, the definition of which was given above, each quark is connected to the others with the help of a gluon field. The gluon is the particle responsible for the formation of nuclear forces.
In addition to the mass in kilograms and atomic mass units, in nuclear physics, the mass of a particle is also described in GeV (gigaelectronvolts). This became possible after Einstein's discovery of his famous equation E=mc 2 , which relates energy to mass. What is a neutron in GeV? This is a value of 0.0009396, which is slightly larger than that of the proton (0.0009383).
Stability of the neutron and atomic nuclei
The presence of neutrons in atomic nuclei is very important for their stability and the possibility of the existence of the atomic structure itself and matter in general. The fact is that protons, which also make up the atomic nucleus, have a positive charge. And their approach to close distances requires the expenditure of huge energies due to the Coulomb electric repulsion. The nuclear forces acting between neutrons and protons are 2-3 orders of magnitude stronger than the Coulomb ones. Therefore, they are able to keep positively charged particles at close distances. Nuclear interactions are short-range and manifest themselves only within the size of the nucleus.
The neutron formula is used to find their number in the nucleus. It looks like this: the number of neutrons = the atomic mass of the element - the atomic number in the periodic table.
A free neutron is an unstable particle. Its average lifetime is 15 minutes, after which it decays into three particles:
- electron;
- proton;
- antineutrino.
Prerequisites for the discovery of the neutron
The theoretical existence of the neutron in physics was proposed back in 1920 by Ernest Rutherford, who tried to explain in this way why atomic nuclei do not fall apart due to the electromagnetic repulsion of protons.
Even earlier, in 1909 in Germany, Bothe and Becker established that if light elements, such as beryllium, boron or lithium, are irradiated with high-energy alpha particles from polonium, then radiation is formed that passes through any thickness of various materials. They assumed that it was gamma radiation, but no such radiation known at that time had such a great penetrating power. The experiments of Bothe and Becker have not been properly interpreted.
Discovery of the neutron
The existence of the neutron was discovered by the English physicist James Chadwick in 1932. He studied the radioactive radiation of beryllium, conducted a series of experiments, obtaining results that did not coincide with those predicted by physical formulas: the energy of radioactive radiation far exceeded theoretical values, and the law of conservation of momentum was also violated. Therefore, it was necessary to accept one of the hypotheses:
- Or angular momentum is not conserved in nuclear processes.
- Or radioactive radiation consists of particles.
The scientist rejected the first assumption, since it contradicts the fundamental physical laws, so he accepted the second hypothesis. Chadwick showed that the radiation in his experiments was formed by particles with zero charge, which have a strong penetrating power. In addition, he was able to measure the mass of these particles, establishing that it is slightly larger than that of a proton.
Slow and fast neutrons
Depending on the energy that a neutron has, it is called slow (of the order of 0.01 MeV) or fast (of the order of 1 MeV). Such a classification is important, since some of its properties depend on the speed of the neutron. In particular, fast neutrons are well captured by nuclei, leading to the formation of their isotopes, and causing their fission. Slow neutrons are poorly captured by the nuclei of almost all materials, so they can easily pass through thick layers of matter.
The role of the neutron in the fission of the uranium nucleus
If you ask yourself what a neutron is in nuclear energy, then we can say with confidence that this is a means of inducing the process of fission of the uranium nucleus, accompanied by the release of large energy. This fission reaction also produces neutrons of various speeds. In turn, the generated neutrons induce the decay of other uranium nuclei, and the reaction proceeds in a chain manner.
If the uranium fission reaction is uncontrolled, then this will lead to an explosion of the reaction volume. This effect is used in nuclear bombs. The controlled fission reaction of uranium is the source of energy in nuclear power plants.
What is a neutron? What are its structure, properties and functions? Neutrons are the largest of the particles that make up atoms, which are the building blocks of all matter.
Atom structure
Neutrons are located in the nucleus - a dense region of the atom, also filled with protons (positively charged particles). These two elements are held together by a force called nuclear. Neutrons have a neutral charge. The positive charge of the proton is matched with the negative charge of the electron to create a neutral atom. Although neutrons in the nucleus do not affect the charge of an atom, they do have many properties that affect an atom, including the level of radioactivity.
Neutrons, isotopes and radioactivity
A particle that is in the nucleus of an atom - a neutron is 0.2% larger than a proton. Together they make up 99.99% of the total mass of the same element and can have a different number of neutrons. When scientists refer to atomic mass, they mean the average atomic mass. For example, carbon usually has 6 neutrons and 6 protons with an atomic mass of 12, but sometimes it occurs with an atomic mass of 13 (6 protons and 7 neutrons). Carbon with atomic number 14 also exists, but is rare. So the atomic mass for carbon averages out to 12.011.
When atoms have different numbers of neutrons, they are called isotopes. Scientists have found ways to add these particles to the nucleus to create large isotopes. Now adding neutrons does not affect the charge of the atom, since they have no charge. However, they increase the radioactivity of the atom. This can result in very unstable atoms that can discharge high levels of energy.
What is a core?
In chemistry, the nucleus is the positively charged center of an atom, which is made up of protons and neutrons. The word "core" comes from the Latin nucleus, which is a form of the word meaning "nut" or "core". The term was coined in 1844 by Michael Faraday to describe the center of an atom. The sciences involved in the study of the nucleus, the study of its composition and characteristics, are called nuclear physics and nuclear chemistry.
Protons and neutrons are held together by the strong nuclear force. Electrons are attracted to the nucleus, but move so fast that their rotation is carried out at some distance from the center of the atom. The positive nuclear charge comes from protons, but what is a neutron? It is a particle that has no electrical charge. Almost all of the weight of an atom is contained in the nucleus, since protons and neutrons have much more mass than electrons. The number of protons in an atomic nucleus determines its identity as an element. The number of neutrons indicates which isotope of an element is an atom.
Atomic nucleus size
The nucleus is much smaller than the overall diameter of the atom because the electrons can be further away from the center. A hydrogen atom is 145,000 times larger than its nucleus, and a uranium atom is 23,000 times larger than its center. The hydrogen nucleus is the smallest because it consists of a single proton.
Location of protons and neutrons in the nucleus
The proton and neutrons are usually depicted as packed together and uniformly distributed over spheres. However, this is a simplification of the actual structure. Each nucleon (proton or neutron) can occupy a certain energy level and range of locations. While the nucleus may be spherical, it may also be pear-shaped, globular, or disc-shaped.
The nuclei of protons and neutrons are baryons, consisting of the smallest, called quarks. The attractive force has a very short range, so protons and neutrons must be very close to each other in order to be bound. This strong attraction overcomes the natural repulsion of charged protons.
Proton, neutron and electron
A powerful impetus in the development of such a science as nuclear physics was the discovery of the neutron (1932). Thanks for this should be an English physicist who was a student of Rutherford. What is a neutron? This is an unstable particle, which in a free state in just 15 minutes is able to decay into a proton, an electron and a neutrino, the so-called massless neutral particle.
The particle got its name due to the fact that it has no electric charge, it is neutral. Neutrons are extremely dense. In an isolated state, one neutron will have a mass of only 1.67·10 - 27, and if you take a teaspoon densely packed with neutrons, then the resulting piece of matter will weigh millions of tons.
The number of protons in the nucleus of an element is called the atomic number. This number gives each element its own unique identity. In the atoms of some elements, such as carbon, the number of protons in the nuclei is always the same, but the number of neutrons may vary. An atom of a given element with a certain number of neutrons in the nucleus is called an isotope.
Are single neutrons dangerous?
What is a neutron? This is a particle that, along with the proton, is included in However, sometimes they can exist on their own. When neutrons are outside the nuclei of atoms, they acquire potentially dangerous properties. When they move at high speed, they produce lethal radiation. Known for their ability to kill humans and animals, so-called neutron bombs have minimal impact on non-living physical structures.
Neutrons are a very important part of an atom. The high density of these particles, combined with their speed, gives them extraordinary destructive power and energy. As a consequence, they can alter or even tear apart the nuclei of atoms that strike. Although the neutron has a net neutral electrical charge, it is made up of charged components that cancel each other out with respect to charge.
The neutron in an atom is a tiny particle. Like protons, they're too small to see even with an electron microscope, but they're there because that's the only way to explain the behavior of atoms. Neutrons are very important for the stability of an atom, but outside of its atomic center they cannot exist for a long time and decay on average in only 885 seconds (about 15 minutes).
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