What does a proton, neutron and electron consist of? Structure of the atomic nucleus (proton, neutron, electron)

Chapter first. PROPERTIES OF STABLE NUCLEI

It was already said above that the nucleus consists of protons and neutrons bound by nuclear forces. If we measure the mass of a nucleus in atomic mass units, it should be close to the mass of a proton multiplied by an integer called the mass number. If the charge of a nucleus is a mass number, this means that the nucleus contains protons and neutrons. (The number of neutrons in the nucleus is usually denoted by

These properties of the kernel are reflected in symbolic notation, which will be used later in the form

where X is the name of the element whose atom the nucleus belongs to (for example, nuclei: helium - , oxygen - , iron - uranium

The main characteristics of stable nuclei include: charge, mass, radius, mechanical and magnetic moments, spectrum of excited states, parity and quadrupole moment. Radioactive (unstable) nuclei are additionally characterized by their lifetime, type of radioactive transformations, energy of emitted particles and a number of other special properties, which will be discussed below.

First of all, let's consider the properties of the elementary particles that make up the nucleus: proton and neutron.

§ 1. BASIC CHARACTERISTICS OF THE PROTON AND NEUTRON

Weight. In units of electron mass: proton mass, neutron mass.

In atomic mass units: proton mass, neutron mass

In energy units, the rest mass of a proton is the rest mass of a neutron.

Electric charge. q is a parameter characterizing the interaction of a particle with an electric field, expressed in units of electron charge where

All elementary particles carry an amount of electricity equal to either 0 or The charge of a proton The charge of a neutron is zero.

Spin. The spins of the proton and neutron are equal. Both particles are fermions and obey Fermi-Dirac statistics, and therefore the Pauli principle.

Magnetic moment. If we substitute the proton mass into formula (10), which determines the magnetic moment of the electron instead of the electron mass, we obtain

The quantity is called nuclear magneton. It could be assumed by analogy with the electron that the spin magnetic moment of the proton is equal to However, experience has shown that the proton’s own magnetic moment is greater than the nuclear magneton: according to modern data

In addition, it turned out that an uncharged particle - a neutron - also has a magnetic moment that is different from zero and equal to

The presence of a magnetic moment in a neutron and so great importance magnetic moment of the proton contradict assumptions about the point nature of these particles. A number of experimental data obtained in last years, indicates that both the proton and the neutron have a complex inhomogeneous structure. At the center of the neutron there is a positive charge, and at the periphery there is a negative charge equal in magnitude distributed in the volume of the particle. But since the magnetic moment is determined not only by the magnitude of the flowing current, but also by the area covered by it, the magnetic moments created by them will not be equal. Therefore, a neutron can have a magnetic moment while remaining generally neutral.

Mutual transformations of nucleons. The mass of a neutron is 0.14% greater than the mass of a proton, or 2.5 times the mass of an electron,

In a free state, a neutron decays into a proton, electron and antineutrino: Its average lifetime is close to 17 minutes.

A proton is a stable particle. However, inside the nucleus it can turn into a neutron; in this case the reaction proceeds according to the scheme

The difference in the masses of particles on the left and right is compensated by the energy imparted to the proton by other nucleons in the nucleus.

A proton and a neutron have the same spins, almost the same masses, and can transform into each other. It will be shown later that the nuclear forces acting between these particles in pairs are also identical. Therefore, they are called by a common name - nucleon and they say that a nucleon can be in two states: proton and neutron, differing in their relationship to the electromagnetic field.

Neutrons and protons interact due to the existence of nuclear forces that are non-electrical in nature. Nuclear forces owe their origin to the exchange of mesons. If we depict the dependence of the potential energy of interaction between a proton and a low-energy neutron on the distance between them, then approximately it will look like the graph shown in Fig. 5, a, i.e. it has the shape of a potential well.

Rice. 5. Dependence of potential interaction energy on the distance between nucleons: a - for neutron-neutron or neutron-proton pairs; b - for a proton-proton pair

As soon as you happen to encounter an unknown object, the mercantile and everyday question inevitably arises - how much does it weigh? But if this unknown is an elementary particle, what then? But nothing, the question remains the same: what is the mass of this particle. If someone were to start counting the costs incurred by humanity to satisfy their curiosity in researching, or rather, measuring, the mass of elementary particles, we would find out that, for example, the mass of a neutron in kilograms with a mind-boggling number of zeros after the decimal point cost humanity more than than the most expensive construction with the same number of zeros before the decimal point.

And it all started very routinely: in 1897, in the laboratory headed by J. J. Thomson, studies of cathode rays were carried out. As a result, a universal constant for the Universe was determined - the ratio of the mass of an electron to its charge. There is very little left to determine the mass of the electron - to determine its charge. After 12 years I managed to do it. He conducted experiments with oil droplets falling in an electric field, and he managed not only to balance their weight with the magnitude of the field, but also to carry out the necessary and extremely subtle measurements. Their result is the numerical value of the electron mass:

me = 9.10938215(15) * 10-31kg.

Research into the structure, where Ernest Rutherford was a pioneer, also dates back to this time. It was he who, observing the scattering of charged particles, proposed a model of the atom with an external electron shell and a positive core. The particle, which was proposed to play the role of the nucleus of the simplest atom, was obtained by bombarding nitrogen. This was the first nuclear reaction, obtained in the laboratory - as a result, oxygen and nuclei of future ones called protons were obtained from nitrogen. However, alpha rays consist of complex particles: in addition to two protons, they also contain two neutrons. The mass of the neutron is almost equal to total weight The alpha particle turns out to be quite substantial in order to destroy the oncoming nucleus and break off a “piece” from it, which is what happened.

The flow of positive protons was deflected by the electric field, compensating for its deflection caused by In these experiments, determining the mass of the proton was no longer difficult. But the most interesting question was what the ratio of the mass of a proton and an electron is. The riddle was immediately solved: the mass of a proton exceeds the mass of an electron a little more than 1836 times.

So, initially, the model of the atom was assumed, according to Rutherford, to be an electron-proton set with the same number of protons and electrons. However, it soon turned out that the primary nuclear model does not fully describe all the observed effects in the interactions of elementary particles. Only in 1932 did he confirm the hypothesis of additional particles in the nucleus. They were called neutrons, neutral protons, because. they had no charge. It is this circumstance that determines their greater penetrating ability - they do not spend their energy on ionizing oncoming atoms. The mass of a neutron is very slightly greater than the mass of a proton - only about 2.6 electron masses more.

The chemical properties of substances and compounds that are formed by a given element are determined by the number of protons in the nucleus of the atom. Over time, the participation of the proton in strong and other fundamental interactions was confirmed: electromagnetic, gravitational and weak. Moreover, despite the fact that the neutron has no charge, in strong interactions the proton and neutron are considered as an elementary particle, the nucleon, in various quantum states. The similarity in the behavior of these particles is partly explained by the fact that the mass of a neutron differs very little from the mass of a proton. The stability of protons allows them to be used, after being previously accelerated to high speeds, as bombarding particles to carry out nuclear reactions.

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. Considering that it is this element that heads 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 constant value, characterizes chemical and physical properties of this 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 physical and Chemical properties specific chemical element.

What is a neutron? What are its structure, properties and functions? Neutrons are the largest of the particles that make up atoms, the building blocks of all matter.

Atomic structure

Neutrons are found 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. Even though the neutrons in the nucleus do not affect the charge of the atom, they still have many properties that affect the atom, including the level of radioactivity.

Neutrons, isotopes and radioactivity

A particle that is located in the nucleus of an atom is a neutron that is 0.2% larger than a proton. Together they make up 99.99% of the total mass of the same element can have different quantity neutrons. When scientists refer to atomic mass, they mean average atomic mass. For example, carbon typically has 6 neutrons and 6 protons with an atomic mass of 12, but it is sometimes found with an atomic mass of 13 (6 protons and 7 neutrons). Carbon with atomic number 14 also exists, but is rare. So, atomic mass for carbon averages 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 larger 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 lead to very unstable atoms that can discharge high levels energy.

What is the core?

In chemistry, the nucleus is the positively charged center of an atom, which consists of protons and neutrons. The word "kernel" comes from the Latin nucleus, which is a form of the word meaning "nut" or "kernel". 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 strong nuclear force. The electrons are attracted to the nucleus, but move so fast that their rotation occurs at some distance from the center of the atom. The nuclear charge with a plus sign comes from protons, but what is a neutron? This is a particle that has no electrical charge. Almost all the weight of an atom is contained in the nucleus, since protons and neutrons have much large 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 the element the atom is.

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.

Arrangement of protons and neutrons in the nucleus

The proton and neutrons are usually depicted as being packed together and evenly distributed into spheres. However, this is a simplification of the actual structure. Each nucleon (proton or neutron) can occupy a specific energy level and range of locations. While the nucleus can be spherical, it can also be pear-shaped, spherical, or disc-shaped.

The nuclei of protons and neutrons are baryons, consisting of smallest ones called quarks. The attractive force has a very short range, so protons and neutrons must be very close to each other 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). We should thank for this the English physicist who was a student of Rutherford. What is a neutron? This is an unstable particle that, in a free state, can decay into a proton, electron and neutrino, the so-called massless neutral particle, in just 15 minutes.

The particle gets its name because it has no electrical 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, 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 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 can 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 potential dangerous properties. When they move with high speed, they produce deadly radiation. So called neutron bombs, known for their ability to kill people and animals, while having minimal effect on non-living physical structures.

Neutrons are a very important part of the atom. The high density of these particles, combined with their speed, gives them extreme destructive power and energy. As a result, they can alter or even tear apart the nuclei of the atoms they strike. Although a neutron has a net neutral electrical charge, it is composed of charged components that cancel each other with respect to charge.

A neutron in an atom is a tiny particle. Like protons, they are too small to be seen even with an electron microscope, but they are there because that is the only way to explain the behavior of atoms. Neutrons are very important for the stability of an atom, but outside its atomic center they cannot exist for long and decay on average in only 885 seconds (about 15 minutes).

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! From a modern point of view, the proton is not a truly 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 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, a special number was introduced - the 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 possible education chemical elements and ultimately the emergence of intelligent life. 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. Opened in 1932 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.