Since ancient times, man has been interested in the structure of the matter that he observes around him every day. One of the hypotheses, put forward in ancient Greece, postulated that matter consists of elementary particles - atoms. However, only in the 20th century it was experimentally established that the atom also consists of subatomic particles: protons, electrons and neutrons. The article reveals the topic of who discovered the neutron, proton and electron, and what impact these discoveries had on the development of mankind.

Atom and subatomic particles

The matter of the universe is made up of small particles called atoms. This concept was put forward by the Greek mathematician and philosopher Democritus as early as the 5th century BC. From the ancient Greek language, the word "atom" is translated as "indivisible". Due to the technical impossibility of verifying what an atom is, this hypothesis existed until the 19th century, when advances in science and technology made it possible to study the atom more carefully. Through the study of the atom late XIX century, it was found that it is not an elementary unit of matter and consists of smaller particles, which were called subatomic. It is customary to refer to these particles as the electron, proton and neutron, since they form the atoms of all matter.

At present, science has advanced far ahead in the study of elementary particles. So, it was found that even subatomic particles also have their own internal structure. In addition, there is the so-called antimatter, formed by atoms, consisting of antiparticles, which are also subatomic. Nevertheless, the discovery of electrons, protons and neutrons marked the beginning of nuclear physics and the nuclear history of mankind. Who discovered these subatomic particles is discussed in this article.

Modern ideas about the structure of the atom

Before proceeding to the answer to the question of who discovered neutrons, protons and electrons, let's consider what an atom is from a modern point of view.

Every substance we see every day is made up of molecules. They are also made up of atoms. Although the number of different molecules is quite large, they are all formed by a limited number of different atoms (of the order of 100). Each atom has a nucleus, consisting of protons and neutrons, and electrons revolving around the nucleus, the electric charge of which is negative and opposite in sign to the charge of the nucleus.

If we apply these ideas to water, then it should be said that in a drop of water with a diameter of 4 mm there are approximately 10 15 molecules. The water molecule consists of 3 atoms: 2 hydrogen atoms and 1 oxygen atom. The oxygen atom consists of a nucleus, formed by 8 protons and 8 neutrons, and an electron shell, consisting of 8 electrons.

Discovery of the electron

Until 1897, mankind considered the atom to be indivisible, when the British physicist Joseph John Thomson discovered the electron in his experiments with cathode rays. The device that Thomson used was a sealed glass tube in which two cathodes were placed and air was evacuated. The scientist discovered that the emitted cathode rays deviate from the path of their propagation, if they are affected by an electric field. As a result, the scientist found that the particles that form these rays must have a negative charge. Subsequently, these particles were called electrons.

Discovery of the proton

JJ Thomson's student, New Zealand physicist Ernest Rutherford, is credited with discovering the proton. At the beginning of the 20th century, he proposed a planetary model of the structure of the atom, in which the main mass is in the center. Rutherford came to this hypothesis after analyzing experiments in which scientists Hans Geiger and Ernest Marsden bombarded a plate of gold with alpha particles.

In 1918, Rutherford conducted experiments on his own on the interaction of alpha particles with nitrogen. In these experiments, the scientist observed the emission of nuclei of the hydrogen atom and came to the conclusion that they are "bricks" for all other nuclei. So Rutherford discovered the proton. Subsequently, it was found that nuclear mass significantly exceeded the total mass of all the protons of the atom, so Rutherford suggested that in the nucleus of the atom there is still some heavy particle that does not have a charge. This particle was the neutron, which was discovered later.

Who discovered the neutron?

The third particle that makes up the atom was discovered in 1932. The scientist who discovered the existence of neutrons was the English physicist James Chadwick. By studying the behavior of atoms when they are bombarded by alpha particles, Chadwick discovered the existence of radiation, the particles of which had a mass approximately the same as protons, but were electrically neutral because they did not interact with an electric field. In addition, these particles were able to penetrate matter and make atoms heavy elements split into lighter ones. Because of physical properties new particle Chadwick called it a neutron, so he is rightfully considered the scientist who discovered the neutron.

Energy of the atomic nucleus

Since the discovery of neutrons, nuclear physics as well as chemistry and technology have taken a huge step forward. A new, practically inexhaustible and at the same time dangerous source of energy has opened up before man.

The beginning of the nuclear era was felt by mankind in 1945, when the United States tested the devastating first nuclear bomb"Trinity", dropping it on the Japanese cities of Hiroshima and Nagasaki.

The first use of nuclear energy for peaceful purposes should be attributed to the mid-1950s, when the first nuclear power plant was built in 1953. nuclear reactor, which replaced the diesel engine on the American submarine Nautilus.

In 1920, Rutherford conjectured about the existence of a neutral elementary particle formed as a result of the fusion of an electron and a proton. In the thirties, J. Chadwick was invited to the Cavendish Laboratory to conduct experiments to detect this particle. The experiments took place over many years. With the help of an electric discharge through hydrogen, free protons were obtained, with which the nuclei of various elements were bombarded. The calculation was that it would be possible to knock out the desired particle from the nucleus and destroy it, and indirectly record the knockout acts by the tracks of the decaying proton and electron.

In 1930, Bothe and Becker during irradiation a- particles of beryllium found radiation of great penetrating power. Unknown rays passed through lead, concrete, sand, etc. At first it was supposed to be hard x-rays. But this assumption did not stand up to scrutiny. When observing rare acts of collision with nuclei, the latter received such a large return, for the explanation of which it was necessary to assume unusually high energy x-ray photons.

Chadwick decided that in the experiments of Bothe and Becker, the neutral particles that he was trying to detect were emitted from beryllium. He repeated the experiments, hoping to find leaks of neutral particles, but to no avail. Tracks were not found. He set aside his experiments.

The decisive impetus for the resumption of his experiments was an article published by Irene and Frédéric Joliot-Curie on the ability of beryllium radiation to knock out protons from paraffin (January 1932). Taking into account the results of Joliot-Curie, he modified the experiments of Bothe and Becker. The scheme of his new installation is shown in Figure 30. Beryllium radiation was obtained by scattering a- particles on a beryllium plate. A paraffin block was placed in the radiation path. Radiation was found to knock out protons from paraffin.

We now know that the radiation from beryllium is a stream of neutrons. Their mass is almost equal to the mass of a proton, so neutrons transfer most of the energy to protons flying forward. Protons knocked out of paraffin and flying forward had an energy of about 5.3 MeV. Chadwick immediately rejected the possibility of explaining the knocking out of protons by the Compton effect, since in this case it was necessary to assume that the photons scattered by protons had an energy of about 50 MeV(at that time sources of such high-energy photons were not known). Therefore, he concluded that the observed interaction occurs according to the scheme
Joliot-Curie reaction (2)

In this experiment, not only free neutrons were observed for the first time, it was also the first nuclear transformation - the production of carbon by the fusion of helium and beryllium.

Task 1. In Chadwick's experiment, protons knocked out of paraffin had an energy 5.3 MeV. Show that for the acquisition of such energy by protons during the scattering of photons, it is necessary that the photons have the energy 50 MeV.

History of the discovery of the neutron

The history of the discovery of the neutron begins with Chadwick's unsuccessful attempts to detect neutrons in electric discharges in hydrogen (based on the aforementioned Rutherford hypothesis). Rutherford, as we know, carried out the first artificial nuclear reaction by bombarding the nuclei of the atom with alpha particles. This method also succeeded in carrying out artificial reactions with the nuclei of boron, fluorine, sodium, aluminum and phosphorus. In this case, long-range protons were emitted. Subsequently, it was possible to split the nuclei of neon, magnesium, silicon, sulfur, chlorine, argon and potassium. These reactions were confirmed by the experiments of the Viennese physicists Kirsch and Petterson (1924), who also claimed that they were able to split the nuclei of lithium, beryllium and carbon, which Rutherford and his co-workers failed to do.

A discussion broke out in which Rutherford disputed the splitting of these three nuclei. Recently, O. Frisch suggested that the results of the Viennese are explained by the participation in the observations of students who sought to "please" the leaders and saw outbreaks where there were none.

In 1930, Walter Bothe (1891-1957) and H. Becker bombarded beryllium with polonium a-particles. In doing so, they found that beryllium, as well as boron, emit strongly penetrating radiation, which they identified with hard y-radiation.

And in January 1932, Irene and Frederic Joliot-Curie reported at a meeting of the Paris Academy of Sciences the results of studies of radiation discovered by Bothe and Becker. They showed that this radiation "is capable of freeing protons in hydrogen-containing substances, giving them a high speed."

These protons were photographed by them in a cloud chamber.

In the next communication, made on March 7, 1932, Irene and Frédéric Joliot-Curie showed photographs of traces of protons in a cloud chamber knocked out of paraffin by beryllium radiation.

Interpreting their results, they wrote: “Assumptions about elastic collisions of a photon with a nucleus lead to difficulties, consisting, on the one hand, in the fact that this requires a quantum with a significant energy, and, on the other hand, in the fact that this process occurs too often. Chadwick proposes to assume that the radiation excited in beryllium consists of neutrons - particles with unit mass and zero charge.

The results of Joliot-Curie threatened the law of conservation of energy. Indeed, if we try to interpret the Joliot-Curie experiments based on the presence in nature of only known particles: protons, electrons, photons, then the explanation for the appearance of long-range protons requires the production of photons with an energy of 50 MeV in beryllium. In this case, the photon energy turns out to depend on the type of recoil nucleus used to determine the photon energy.

This conflict was resolved by Chadwick. He placed a beryllium source in front of an ionization chamber, into which protons knocked out of a paraffin plate fell. Placing aluminum absorbing screens between the paraffin plate and the chamber, Chadwick found that beryllium radiation knocks out protons with energies up to 5.7 MeV from paraffin. To communicate such energy to protons, a photon must itself have an energy of 55 MeV. But the energy of nitrogen recoil nuclei observed with the same beryllium radiation turns out to be 1.2 MeV. To transfer such energy to nitrogen, the radiation photon must have an energy of at least 90 MeV. The energy conservation law is incompatible with the photon interpretation of beryllium radiation.

Chadwick showed that all difficulties are removed if we assume that beryllium radiation consists of particles with a mass equal approximately to that of a proton and zero charge. He called these particles neutrons. Chadwick published an article about his results in the Proceedings of the Royal Society for 1932. However, a preliminary note on the neutron was published in the Nature issue of February 27, 1932. Subsequently, I. and f. Joliot-Curie in a number of works of 1932-1933. confirmed the existence of neutrons and their ability to knock out protons from light nuclei. They also established the emission of neutrons from argon, sodium, and aluminum nuclei when irradiated with a-rays.

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At the beginning of the 20th century, when it had already been established that molecules were made up of atoms, new question. What are atoms made of? The English scientist Rutherford and a group of his students undertook to solve this difficult problem.

The nucleus of a hydrogen atom in the nucleus of any substance

It was already known that the atom itself consists of a nucleus and an electron rotating around it at high speed. But what is the core made of? Rutherford assumed that the nucleus of an atom of any chemical element necessarily includes the nucleus of a hydrogen atom.

Later, this was proved by a series of experiments. The essence of the experiments was as follows: nitrogen atoms were bombarded with alpha radiation. This led to the fact that periodically alpha radiation knocked out some particles from the nucleus of the nitrogen atom.

The whole process was captured on photosensitive film. However, the glow was still so weak that before starting the experiment, Rutherford and his students sat in a completely dark room for about 8 hours so that the eye could see the smallest light signals.

By the nature of the light traces, it was found that the knocked-out particles are the nuclei of oxygen and hydrogen atoms. Thus, Rutherford's assumption that the nucleus of the hydrogen atom is part of the nucleus of the atom of any chemical element was confirmed.

Discovery of the proton

Rutherford called this particle a proton. From the Greek "protos" - the first. It should be understood that it is not the proton that is the nucleus of the hydrogen atom, but, on the contrary, the nucleus of the hydrogen atom has such a structure that only one proton enters it.

The composition of the nuclei of atoms of other chemical elements may include much more protons. The proton has a positive electrical charge. In this case, the charge of the proton is equal to the charge of the electron, but it has a different sign.

Thus, the proton and electron seem to balance each other. Therefore, all objects are initially not charged in any way, and acquire a charge only when they enter an electric field.

Discovery of the neutron

After the discovery of the proton, scientists understood that the nucleus consists not only of protons, since, using the example of the nucleus of the beryllium atom, it turned out that the total mass of protons in the nucleus is 4 mass units, while the mass of the nucleus as a whole is 9 mass units.

That is, another 5 units of mass belong to some other particles, which, moreover, do not have an electric charge, since otherwise the proton-electron balance would be disturbed.

Rutherford's student Chadwick conducted a series of experiments and discovered particles emitted from the nucleus of a beryllium atom when bombarded with alpha radiation, but having no charge.

The absence of charge was stated by the fact that the particles did not react in any way to the electromagnetic field. It became obvious that the missing element of the structure of the atomic nucleus had been discovered.

These particles were called neutrons. The neutron has a mass approximately equal to the mass of the proton, but at the same time, as already mentioned, it does not have any charge.

Since ancient times, man has been interested in the structure of the matter that he observes around him every day. One of the hypotheses, put forward in ancient Greece, ...

Who discovered the neutron, proton and electron, and what significance did this have for mankind

By Masterweb

01.08.2018 14:00

Since ancient times, man has been interested in the structure of the matter that he observes around him every day. One of the hypotheses, put forward in ancient Greece, postulated that matter consists of elementary particles - atoms. However, only in the 20th century it was experimentally established that the atom also consists of subatomic particles: protons, electrons and neutrons. The article reveals the topic of who discovered the neutron, proton and electron, and what impact these discoveries had on the development of mankind.

Atom and subatomic particles

The matter of the universe is made up of small particles called atoms. This concept was put forward by the Greek mathematician and philosopher Democritus as early as the 5th century BC. From the ancient Greek language, the word "atom" is translated as "indivisible". Due to the technical impossibility of verifying what an atom is, this hypothesis existed until the 19th century, when advances in science and technology made it possible to study the atom more carefully. Thanks to the study of the atom at the end of the 19th century, it was found that it is not an elementary unit of matter and consists of smaller particles, which were called subatomic. It is customary to refer to these particles as the electron, proton and neutron, since they form the atoms of all matter.

At present, science has advanced far ahead in the study of elementary particles. So, it was found that even subatomic particles also have their own internal structure. In addition, there is the so-called antimatter, formed by atoms, consisting of antiparticles, which are also subatomic. Nevertheless, the discovery of electrons, protons and neutrons marked the beginning of nuclear physics and the nuclear history of mankind. Who discovered these subatomic particles is discussed in this article.

Modern ideas about the structure of the atom

Before proceeding to the answer to the question of who discovered neutrons, protons and electrons, let's consider what an atom is from a modern point of view.

Every substance we see every day is made up of molecules. They are also made up of atoms. Although the number of different molecules is quite large, they are all formed by a limited number of different atoms (of the order of 100). Each atom has a nucleus, consisting of protons and neutrons, and electrons revolving around the nucleus, the electric charge of which is negative and opposite in sign to the charge of the nucleus.

If we apply these ideas to water, then we should say that in a drop of water with a diameter of 4 mm there are approximately 1015 molecules. The water molecule consists of 3 atoms: 2 hydrogen atoms and 1 oxygen atom. The oxygen atom consists of a nucleus, formed by 8 protons and 8 neutrons, and an electron shell, consisting of 8 electrons.

Discovery of the electron

Until 1897, mankind considered the atom to be indivisible, when the British physicist Joseph John Thomson discovered the electron in his experiments with cathode rays. The device that Thomson used was a sealed glass tube in which two cathodes were placed and air was evacuated. The scientist discovered that the emitted cathode rays deviate from the path of their propagation, if they are affected by an electric field. As a result, the scientist found that the particles that form these rays must have a negative charge. Subsequently, these particles were called electrons.

Discovery of the proton

JJ Thomson's student, New Zealand physicist Ernest Rutherford, is credited with discovering the proton. At the beginning of the 20th century, he proposed a planetary model of the structure of the atom, in which the main mass is in the center. Rutherford came to this hypothesis after analyzing experiments in which scientists Hans Geiger and Ernest Marsden bombarded a plate of gold with alpha particles.

In 1918, Rutherford conducted experiments on his own on the interaction of alpha particles with nitrogen. In these experiments, the scientist observed the emission of nuclei of the hydrogen atom and came to the conclusion that they are "bricks" for all other nuclei. So Rutherford discovered the proton. Subsequently, it was found that the nuclear mass significantly exceeded the total mass of all the protons of the atom, so Rutherford suggested that in the nucleus of the atom there is still some heavy particle that does not have a charge. This particle was the neutron, which was discovered later.

Who discovered the neutron?

The third particle that makes up the atom was discovered in 1932. The scientist who discovered the existence of neutrons was the English physicist James Chadwick. By studying the behavior of atoms when they are bombarded by alpha particles, Chadwick discovered the existence of radiation, the particles of which had a mass approximately the same as protons, but were electrically neutral because they did not interact with an electric field. In addition, these particles were able to penetrate matter and force the atoms of heavy elements to divide into lighter ones. Because of the physical properties of the new particle, Chadwick called it the neutron, so he is rightfully considered the scientist who discovered the neutron.

Energy of the atomic nucleus

Since the discovery of neutrons, nuclear physics as well as chemistry and technology have taken a huge step forward. A new, practically inexhaustible and at the same time dangerous source of energy has opened up before man.

The beginning of the nuclear era was felt by mankind in 1945, when the United States tested the devastating first nuclear bomb Trinity, dropping it on the Japanese cities of Hiroshima and Nagasaki.

The first use of nuclear energy for peaceful purposes can be traced back to the mid-1950s, when the first nuclear reactor was built in 1953 to replace the diesel engine on the American submarine Nautilus.

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