Which is bigger, neutron or proton? The structure of atoms - elementary particles of matter, electrons, protons, neutrons

A proton is a stable particle from the class of hadrons, the nucleus of a hydrogen atom.

It is difficult to say which event should be considered the discovery of the proton: after all, as a hydrogen ion, it has been known for a long time. The creation of a planetary model of the atom by E. Rutherford (1911), the discovery of isotopes (F. Soddy, J. Thomson, F. Aston, 1906-1919), and the observation of hydrogen nuclei knocked out of nuclei by alpha particles played a role in the discovery of the proton nitrogen (E. Rutherford, 1919). In 1925, P. Blackett received the first photographs of proton traces in a cloud chamber (see Nuclear Radiation Detectors), confirming the discovery of the artificial transformation of elements. In these experiments, the β-particle was captured by a nitrogen nucleus, which emitted a proton and turned into an oxygen isotope.

Together with neutrons, protons form the atomic nuclei of all chemical elements, and the number of protons in the nucleus determines the atomic number of a given element. A proton has a positive electric charge equal to the elementary charge, i.e., the absolute value of the charge of the electron. This has been tested experimentally with an accuracy of 10-21. Proton mass mp = (938.2796 ± 0.0027) MeV or ~ 1.6-10-24 g, i.e. a proton is 1836 times heavier than an electron! WITH modern point From a perspective, the proton is not a true elementary particle: it consists of two u-quarks with electric charges +2/3 (in units of elementary charge) and one d-quark with electric charge -1/3. Quarks are interconnected by the exchange of other hypothetical particles - gluons, quanta of the field that carries strong interactions. Data from experiments in which the processes of electron scattering on protons were considered indeed indicate the presence of point scattering centers inside protons. These experiments are in a certain sense very similar to Rutherford's experiments that led to the discovery of the atomic nucleus. Being a composite particle, the proton has a finite size of ~ 10-13 cm, although, of course, it cannot be represented as a solid ball. Rather, the proton resembles a cloud with a fuzzy boundary, consisting of created and annihilated virtual particles. The proton, like all hadrons, participates in each of the fundamental interactions. So. strong interactions bind protons and neutrons in nuclei, electromagnetic interactions bind protons and electrons in atoms. Examples of weak interactions are the beta decay of a neutron or the intranuclear transformation of a proton into a neutron with the emission of a positron and neutrino (for a free proton such a process is impossible due to the law of conservation and transformation of energy, since the neutron has a slightly larger mass). The proton spin is 1/2. Hadrons with half-integer spin are called baryons (from the Greek word meaning "heavy"). Baryons include the proton, neutron, various hyperons (?, ?, ?, ?) and a number of particles with new quantum numbers, most of which have not yet been discovered. To characterize baryons it is introduced special number-- baryon charge, equal to 1 for baryons, - 1 -- for antibaryons and O -- for all other particles. The baryon charge is not a source of the baryon field; it was introduced only to describe the patterns observed in reactions with particles. These patterns are expressed in the form of the law of conservation of baryon charge: the difference between the number of baryons and antibaryons in the system is conserved in any reaction. The conservation of the baryon charge makes it impossible for the proton to decay, since it is the lightest of the baryons. This law is empirical in nature and, of course, must be tested experimentally. The accuracy of the law of conservation of baryon charge is characterized by the stability of the proton, the experimental estimate for the lifetime of which gives a value of no less than 1032 years.

At the same time, theories that combine all types of fundamental interactions predict processes leading to the disruption of the baryon charge and the decay of the proton. The lifetime of a proton in such theories is not very accurately indicated: approximately 1032 ± 2 years. This time is enormous, it is many times longer than the existence of the Universe (~ 2*1010 years). Therefore, the proton is practically stable, which made the formation of chemical elements and ultimately the emergence of intelligent life possible. However, the search for proton decay now represents one of the most important tasks experimental physics. With a proton lifetime of ~ 1032 years in a volume of water of 100 m3 (1 m3 contains ~ 1030 protons), one proton decay per year should be expected. All that remains is to register this decay. The discovery of proton decay will be an important step towards a correct understanding of the unity of the forces of nature.

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 a neutron qn is zero. This is confirmed by direct measurements of the charge from the deflection of a neutron beam in strong electric fields, which showed that |qn|<10-20e (здесь е -- элементарный электрический заряд, т. е. абсолютная величина заряда электрона). Косвенные данные дают оценку |qn|< 2?10-22 е. Спин нейтрона равен 1/2. Как адрон с полуцелым спином, он относится к группе барионов. У каждого бариона есть античастица; антинейтрон был открыт в 1956 г. в опытах по рассеянию антипротонов на ядрах. Антинейтрон отличается от нейтрона знаком барионного заряда; у нейтрона, как и у протона, барионный заряд равен +1.Как и протон и прочие адроны, нейтрон не является истинно элементарной частицей: он состоит из одного u-кварка с электрическим зарядом +2/3 и двух d-кварков с зарядом - 1/3, связанных между собой глюонным полем.

Neutrons are stable only in stable atomic nuclei. A free neutron is an unstable particle that decays into a proton (p), electron (e-) and electron antineutrino. The neutron lifetime is (917?14) s, i.e. about 15 minutes. In matter, neutrons exist in free form even less due to their strong absorption by nuclei. Therefore, they occur in nature or are produced in the laboratory only as a result of nuclear reactions.

Based on the energy balance of various nuclear reactions, the difference between the masses of the neutron and proton was determined: mn-mp(1.29344 ±0.00007) MeV. By comparing it with the proton mass, we obtain the neutron mass: mn = 939.5731 ± 0.0027 MeV; this corresponds to mn ~ 1.6-10-24. The neutron participates in all types of fundamental interactions. Strong interactions bind neutrons and protons in atomic nuclei. An example of the weak interaction is the beta decay of a neutron.

Does this neutral particle participate in electromagnetic interactions? The neutron has an internal structure, and with 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, for which an upper limit was obtained, gained great interest. Here, the most effective experiments were carried out by scientists from the Leningrad Institute of Nuclear Physics of the USSR Academy of Sciences; The search for the neutron dipole moment is important for understanding the mechanisms of violation of invariance under time reversal in microprocesses.

Gravitational interactions of neutrons were observed directly from their incidence in the Earth's gravitational field.

A conventional classification of neutrons according to their kinetic energy is now accepted:

slow neutrons (<105эВ, есть много их разновидностей),

fast neutrons (105?108eV), high-energy (> 108eV).

Very slow neutrons (10-7 eV), which are called ultracold neutrons, have very interesting properties. It turned out that ultracold neutrons can be accumulated in “magnetic traps” and their spins can even be oriented in a certain direction there. Using magnetic fields of a special configuration, ultracold neutrons are isolated from the absorbing walls and can “live” in the trap until they decay. This allows many subtle experiments to study the properties of neutrons. Another method for storing ultracold neutrons is based on their wave properties. Such neutrons can simply be stored in a closed “jar”. This idea was expressed by the Soviet physicist Ya. B. Zeldovich in the late 1950s, and the first results were obtained in Dubna at the Institute of Nuclear Research almost a decade later.

Recently, 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, one can observe resonance effects, diffraction scattering in crystals, etc. Due to these properties, neutrons are widely used in nuclear physics and solid state physics. They play an important role in nuclear energy, in the production of transuranium elements and radioactive isotopes, and find practical application in chemical analysis and geological exploration.

Atoms are the smallest particles of matter.
If you enlarge an average-sized apple to the size of the Earth, the atoms will become only the size of an apple. Despite such small dimensions, the atom consists of even smaller physical particles.
You should already be familiar with the structure of the atom from your school physics course. And yet, let us recall that the atom contains a nucleus and electrons, which rotate around the nucleus so quickly that they become indistinguishable - they form an “electron cloud”, or the electron shell of the atom.

Electrons usually denoted as follows: e − . Electrons e− very light, almost weightless, but they have negative electric charge. It is equal to −1. The electric current we all use is a stream of electrons running in wires.

Atomic nucleus, in which almost all of its mass is concentrated, consists of particles of two types - neutrons and protons.

Neutrons denoted as follows: n 0 , A protons So: p + .
In terms of mass, neutrons and protons are almost the same - 1.675 10−24 g and 1.673 10−24 g.
True, it is very inconvenient to count the mass of such small particles in grams, so it is expressed in carbon units, each of which is equal to 1.673 10 −24 g.
For each particle we get relative atomic mass, equal to the quotient of the mass of an atom (in grams) divided by the mass of a carbon unit. The relative atomic masses of a proton and a neutron are equal to 1, but the charge of protons is positive and equal to +1, while neutrons have no charge.

. Riddles about the atom

An atom can be assembled “in the mind” from particles, like a toy or a car from parts of a children’s construction set. It is only necessary to observe two important conditions.

• First condition: each type of atom has its own own set"details" - elementary particles. For example, a hydrogen atom will definitely have a nucleus with a positive charge of +1, which means it must certainly have one proton (and no more).
  A hydrogen atom can also contain neutrons. More on this in the next paragraph.
  The oxygen atom (atomic number in the Periodic Table is 8) will have a nucleus charged eight positive charges (+8), which means there are eight protons. Since the mass of an oxygen atom is 16 relative units, to get an oxygen nucleus, we add another 8 neutrons.
• Second condition is that each atom should be electrically neutral. To do this, it must have enough electrons to balance the charge of the nucleus. In other words, the number of electrons in an atom is equal to the number of protons in its core, as well as the serial number of this element in the Periodic Table.

As already noted, an atom consists of three types of elementary particles: protons, neutrons and electrons. The atomic nucleus is the central part of an atom, consisting of protons and neutrons. Protons and neutrons have the common name nucleon; they can transform into each other in the nucleus. The nucleus of the simplest atom - the hydrogen atom - consists of one elementary particle - the proton.

The diameter of the nucleus of an atom is approximately 10-13 - 10-12 cm and is 0.0001 of the diameter of the atom. However, almost the entire mass of the atom (99.95-99.98%) is concentrated in the nucleus. If it were possible to obtain 1 cm3 of pure nuclear matter, its mass would be 100-200 million tons. The mass of the nucleus of an atom is several thousand times greater than the mass of all the electrons that make up the atom.

Proton- an elementary particle, the nucleus of a hydrogen atom. The mass of a proton is 1.6721 x 10-27 kg, which is 1836 times the mass of an electron. The electric charge is positive and equal to 1.66 x 10-19 C. A coulomb is a unit of electric charge equal to the amount of electricity passing through the cross-section of a conductor in a time of 1 s at a constant current of 1A (ampere).

Each atom of any element contains a certain number of protons in the nucleus. This number is constant for a given element and determines its physical and chemical properties. That is, the number of protons determines what chemical element we are dealing with. For example, if there is one proton in the nucleus, it is hydrogen, if there are 26 protons, it is iron. The number of protons in the atomic nucleus determines the charge of the nucleus (charge number Z) and the atomic number of the element in the periodic table of elements D.I. Mendeleev (atomic number of the element).

Neutron- an electrically neutral particle with a mass of 1.6749 x 10-27 kg, 1839 times the mass of an electron. A neuron in a free state is an unstable particle; it independently turns into a proton with the emission of an electron and an antineutrino. The half-life of neutrons (the time during which half the original number of neutrons decay) is approximately 12 minutes. However, in a bound state inside stable atomic nuclei, it is stable. The total number of nucleons (protons and neutrons) in the nucleus is called the mass number (atomic mass - A). The number of neutrons included in the nucleus is equal to the difference between the mass and charge numbers: N = A - Z.

Electron- an elementary particle, the carrier of the smallest mass - 0.91095x10-27 g and the smallest electric charge - 1.6021x10-19 C. This is a negatively charged particle. The number of electrons in an atom is equal to the number of protons in the nucleus, i.e. the atom is electrically neutral.

Positron- an elementary particle with a positive electric charge, an antiparticle in relation to the electron. The mass of the electron and positron are equal, and the electric charges are equal in absolute value, but opposite in sign.

The different types of nuclei are called nuclides. Nuclide is a type of atom with given numbers of protons and neutrons. In nature, there are atoms of the same element with different atomic masses (mass numbers):
, Cl, etc. The nuclei of these atoms contain the same number of protons, but different numbers of neutrons. Varieties of atoms of the same element that have the same nuclear charge but different mass numbers are called isotopes . Having the same number of protons, but differing in the number of neutrons, isotopes have the same structure of electron shells, i.e. very similar chemical properties and occupy the same place in the periodic table of chemical elements.

They are designated by the symbol of the corresponding chemical element with the index A located at the top left - the mass number, sometimes the number of protons (Z) is also given at the bottom left. For example, radioactive isotopes of phosphorus are designated 32P, 33P, or P and P, respectively. When designating an isotope without indicating the element symbol, the mass number is given after the element designation, for example, phosphorus - 32, phosphorus - 33.

Most chemical elements have several isotopes. In addition to the hydrogen isotope 1H-protium, heavy hydrogen 2H-deuterium and superheavy hydrogen 3H-tritium are known. Uranium has 11 isotopes; in natural compounds there are three (uranium 238, uranium 235, uranium 233). They have 92 protons and 146,143 and 141 neutrons, respectively.

Currently, more than 1900 isotopes of 108 chemical elements are known. Of these, natural isotopes include all stable (about 280 of them) and natural isotopes that are part of radioactive families (46 of them). The rest are classified as artificial; they are obtained artificially as a result of various nuclear reactions.

The term “isotopes” should only be used when we are talking about atoms of the same element, for example, carbon 12C and 14C. If atoms of different chemical elements are meant, it is recommended to use the term “nuclides”, for example, radionuclides 90Sr, 131J, 137Cs.

Let's talk about how to find protons, neutrons and electrons. There are three types of elementary particles in an atom, each with its own elementary charge and mass.

Core structure

In order to understand how to find protons, neutrons and electrons, imagine It is the main part of the atom. Inside the nucleus are protons and neutrons called nucleons. Inside the nucleus, these particles can transform into each other.

For example, to find protons, neutrons and electrons in one, you need to know its serial number. If we take into account that it is this element that heads the periodic table, then its nucleus contains one proton.

The diameter of the atomic nucleus is ten-thousandth of the total size of the atom. It contains the bulk of the entire atom. The mass of the nucleus is thousands of times greater than the sum of all the electrons present in the atom.

Particle characteristics

Let's look at how to find protons, neutrons and electrons in an atom, and learn about their features. A proton is what corresponds to the nucleus of a hydrogen atom. Its mass exceeds the electron by 1836 times. To determine the unit of electricity passing through a conductor with a given cross-section, electric charge is used.

Each atom has a certain number of protons in its nucleus. It is a constant value and characterizes the chemical and physical properties of a given element.

How to find protons, neutrons and electrons in a carbon atom? The atomic number of this chemical element is 6, therefore, the nucleus contains six protons. According to the planetary system, six electrons move in orbits around the nucleus. To determine the number of neutrons from the carbon value (12), we subtract the number of protons (6), we get six neutrons.

For an iron atom, the number of protons corresponds to 26, that is, this element has the 26th atomic number in the periodic table.

A neutron is an electrically neutral particle, unstable in a free state. A neutron can spontaneously transform into a positively charged proton, emitting an antineutrino and an electron. Its average half-life is 12 minutes. Mass number is the total number of protons and neutrons inside the nucleus of an atom. Let's try to figure out how to find protons, neutrons and electrons in an ion? If an atom, during a chemical interaction with another element, acquires a positive oxidation state, then the number of protons and neutrons in it does not change, only electrons become less.

Conclusion

There were several theories regarding the structure of the atom, but none of them were viable. Before the version created by Rutherford, there was no detailed explanation of the location of protons and neutrons inside the nucleus, as well as the rotation of electrons in circular orbits. After the emergence of the theory of the planetary structure of the atom, researchers had the opportunity not only to determine the number of elementary particles in an atom, but also to predict the physical and chemical properties of a specific chemical element.

Many people know well from school that all substances consist of atoms. Atoms, in turn, consist of protons and neutrons that form the nucleus of atoms and electrons located at some distance from the nucleus. Many have also heard that light also consists of particles - photons. However, the world of particles is not limited to this. To date, more than 400 different elementary particles are known. Let's try to understand how elementary particles differ from each other.

There are many parameters by which elementary particles can be distinguished from each other:

• Weight.
• Electric charge.
• Lifetime. Almost all elementary particles have a finite lifetime, after which they decay.
• Spin. It can be considered, very approximately, as a rotational moment.

A few more parameters, or as they are commonly called in the science of quantum numbers. These parameters do not always have a clear physical meaning, but they are needed in order to distinguish some particles from others. All these additional parameters are introduced as some quantities that are preserved in the interaction.

Almost all particles have mass, except photons and neutrinos (according to the latest data, neutrinos have mass, but so small that it is often considered zero). Without mass particles can only exist in motion. All particles have different masses. The electron has the smallest mass, not counting the neutrino. Particles called mesons have a mass 300-400 times greater than the mass of an electron, a proton and a neutron are almost 2000 times heavier than an electron. Particles that are almost 100 times heavier than a proton have now been discovered. Mass (or its energy equivalent according to Einstein’s formula:

is preserved in all interactions of elementary particles.

Not all particles have an electric charge, which means that not all particles are capable of participating in electromagnetic interaction. All freely existing particles have an electric charge that is a multiple of the electron charge. In addition to freely existing particles, there are also particles that are only in a bound state; we will talk about them a little later.

Spin, like other quantum numbers, is different for different particles and characterizes their uniqueness. Some quantum numbers are conserved in some interactions, some in others. All these quantum numbers determine which particles interact with which and how.

The lifetime is also a very important characteristic of a particle, and we will consider it in more detail. Let's start with a note. As we said at the beginning of the article, everything that surrounds us consists of atoms (electrons, protons and neutrons) and light (photons). And where then are hundreds of different types of elementary particles? The answer is simple - everywhere around us, but we don’t notice it for two reasons.

The first of them is that almost all other particles live very short, approximately 10 to the minus 10 power of seconds or less, and therefore do not form such structures as atoms, crystal lattices, etc. The second reason concerns neutrinos; although these particles do not decay, they are subject only to weak and gravitational interactions. This means that these particles interact so little that they are almost impossible to detect.

Let us visualize how well a particle interacts. For example, the flow of electrons can be stopped by a fairly thin sheet of steel, on the order of a few millimeters. This will happen because the electrons will immediately begin to interact with the particles of the steel sheet, will sharply change their direction, emit photons, and thus lose energy quite quickly. This is not the case with the neutrino flow; they can pass through the Earth almost without interactions. And therefore it is very difficult to detect them.

So, most particles live for a very short time, after which they disintegrate. Particle decays are the most common reactions. As a result of decay, one particle breaks up into several others of smaller mass, and they, in turn, decay further. All decays obey certain rules - conservation laws. So, for example, as a result of decay, electric charge, mass, spin and a number of other quantum numbers must be conserved. Some quantum numbers may change during decay, but also subject to certain rules. It is the decay rules that tell us that the electron and proton are stable particles. They can no longer decay subject to the rules of decay, and therefore they are the ones that end the chains of decay.

Here I would like to say a few words about the neutron. A free neutron also decays into a proton and an electron in about 15 minutes. However, this does not happen when the neutron is in the atomic nucleus. This fact can be explained in various ways. For example, when an electron and an extra proton from a decaying neutron appear in the nucleus of an atom, a reverse reaction immediately occurs - one of the protons absorbs an electron and turns into a neutron. This picture is called dynamic equilibrium. It was observed in the universe at an early stage of its development, shortly after the big bang.

In addition to decay reactions, there are also scattering reactions - when two or more particles interact simultaneously, and as a result one or more other particles are obtained. There are also absorption reactions, when two or more particles produce one. All reactions occur as a result of strong weak or electromagnetic interactions. Reactions due to strong interaction are the fastest; the time of such a reaction can reach 10 minus 20 seconds. The speed of reactions occurring due to electromagnetic interaction is lower; here the time can be about 10 minus 8 seconds. For weak interaction reactions, the time can reach tens of seconds and sometimes years.

At the end of the story about particles, let's talk about quarks. Quarks are elementary particles that have an electrical charge that is a multiple of a third of the charge of an electron and that cannot exist in a free state. Their interaction is arranged in such a way that they can only live as part of something. For example, a combination of three quarks of a certain type forms a proton. Another combination produces a neutron. A total of 6 quarks are known. Their different combinations give us different particles, and although not all combinations of quarks are allowed by physical laws, there are quite a lot of particles made up of quarks.

Here the question may arise: how can a proton be called elementary if it consists of quarks? It’s very simple - the proton is elementary, since it cannot be split into its component parts - quarks. All particles that participate in the strong interaction consist of quarks, and at the same time are elementary.

Understanding the interactions of elementary particles is very important for understanding the structure of the universe. Everything that happens to macro bodies is the result of the interaction of particles. It is the interaction of particles that describes the growth of trees on earth, reactions in the interior of stars, radiation from neutron stars, and much more.