Radioactivity as evidence of the complex structure of atoms. The history of discovery, experiments, types of radioactivity

After the periodic law was opened, for a long time one question remained completely incomprehensible for scientists. Why do the properties of chemicals depend on their atomic mass? The researchers could not understand the very reason for the periodicity. They had to deal with the physical law that underlay the periodic system.

The fruit of human hands or a natural phenomenon?

The phenomenon of radiation actually existed always. People from the very beginning of their history lived in the midst of the so-called natural radioactive field. But radioactivity as evidence of the complex structure of the atom became a well-known phenomenon only at the beginning of the 20th century.

Part of the ionizing radiation comes from space to the earth's surface. People are also irradiated from those sources that are contained in the bowels of the Earth and in minerals. Even in the human body are those substances that are commonly called radionuclides. But until the end of the 19th century, scientists could only guess about all this.

Ignorance of radioactivity

Radioactivity as evidence of the complex structure of atoms was unknown to ordinary miners. For example, in the 16th century, on lead mines in Austria, from the so-called mountain disease miners died massively at the age of only 30-40 years. Local women married several times, as the mortality of miners exceeded the mortality rate of the common population by more than 50 times. Then about such reception, as measurement of radioactivity, yet did not know. People could not even imagine that lead ore could contain dangerous uranium. Only in 1879 the doctors found out that "mountain sickness" is actually lung cancer.

Discovery of radioactive processes Becquerel

At the end of the 19th century, investigations were carried out, as a result of which radioactivity as evidence of the complex structure of atoms became apparent to society. In 1896, the researcher AA Becquerel determined that the substances containing uranium can brighten the photographic plate in the dark. Later, the scientist managed to find out that not only uranium possesses such a property. Then the Polish chemist Maria Sklodowska-Curie, together with her husband Pierre Curie, discovered two new radionuclides: polonium and radium.

The experience of Becquerel was quite simple. He took uranium salts, wrapped them in a dark-colored cloth and then exhibited in the sun to see how the energy stored by this substance would re-emit. But one day the scientist noticed that the photographic plate begins to glow even when the uranium salts were not exposed to the sun. This led to the discovery of radioactivity. Becquerel called the unknown rays X-rays (by analogy with the name of the x-ray).

Rutherford's experiments

Then the radioactivity was carried away by the English scientist Ernest Rutherford. In 1899, he conducted an experiment to study this phenomenon. It was concluded in the following. The scientist took the uranium salt and put it in a cylinder made of lead. Through a narrow aperture, a stream of alpha particles was incident on a photographic plate located on top. At the beginning of the experiments, Rutherford did not use an electromagnetic plate.

Therefore, the photographic plate, as in previous experiments, was illuminated at the same point. Then Rutherford began to connect the magnetic field. With its small value, the beam began to split in two. When the magnetic field increased even more, a dark spot appeared on the plate. Thus, various types of radioactivity were discovered: alpha, beta, and gamma radiation.

Conclusions from studies

After all these experiments, radioactivity became known as evidence of the complex structure of atoms. After all, it turned out that it is the processes inside the atomic nucleus that lead to such radiation. It is appropriate to recall here that since the time of Ancient Greece the atom was considered an indivisible particle of the universe. The very word "atom" meant "indivisible." As a result of research scientists learned about spontaneous electromagnetic radiation, as well as about new particles of atoms - so a serious step forward was made by physics. Radioactivity, which was discovered by the luminaries of science at the dawn of the new century, proved that the atom is actually divided into parts.

The structure of the atom

Experimental studies have confirmed that the atom has a complex structure. It consists of a nucleus and negatively charged electrons. In 1932, the domestic researchers D. Ivanenko and E. Gapon, as well as independently by the German physicist Heisenberg, proposed a model of the structure of the atom, called the proton-neutron. According to this concept, the atom consists of particles called protons and neutrons. They are united in a common group of nucleons.

Virtually the entire mass of the atom is in its core. Protons, neutrons and electrons form a category of elementary particles. As a result of experimental research it was established that the serial number of a substance in a periodic system of elements is equal to the charge of its nucleus.

Properties of radionuclides

To understand what radioactivity is and how it is related to the structure of the nucleus of an atom, it is necessary to master a few simple terms. For example, radionuclides are now called radioactive isotopes. They differ from unstable ones because they have different half-lives.

Radioactive isotopes, turning into other isotopes, become sources of ionizing radiation. Different radionuclides have different degrees of instability. Some can decay for hundreds and thousands of years. Such radionuclides are called long-lived. As an example, all isotopes of uranium can serve. The short-lived radionuclides, in contrast, disintegrate very quickly: within seconds, minutes or months.

What is the measure of radioactivity?

The unit of radioactivity is 1 Becquerel. If one decay occurs in one second, then it is said that the activity of one or the other isotope is equal to one Becquerel. Activity - this is the value that allows you to estimate the power of decay arithmetically. Previously, scientists used a different unit of radioactivity - Curie. The ratio between them is as follows: for 1 Ki there are 37 billion Bq.

In this case, it is necessary to differentiate the activity of different amounts of a substance, for example 1 kg and 1 mg. The activity of a certain amount of matter in science is usually called specific activity. This value is inversely proportional to the half-life.

Danger of radioactivity

Radioactivity as evidence of the complex structure of atoms began to be considered one of the most dangerous phenomena. Having learned more about this phenomenon, people began to reasonably fear its consequences. Many people had the impression that the greatest threat could be gamma radiation. But this is not quite true, at least it does not endanger life. Radiation irradiation is much more dangerous due to its penetrating ability. Of course, in gamma rays, this figure is higher than, for example, in beta rays. But the danger is determined not by this indicator, but by the dose.

The same dose can be safe for a person with one body weight and dangerous for another. The effect of ionizing radiation is determined using the absorbed dose rate. But even this is not enough to assess harm. After all, not every radiation is equally dangerous. The radiation hazard factor is called a weighing factor. The unit of radioactivity used to estimate the radiation dose with a weighting factor is called a sievert.