After the periodic law was opened, for a long time one question remained completely incomprehensible to scientists. Why do the properties of chemicals depend on their atomic mass? Researchers could not understand the very cause of periodicity. They had to deal with the physical law underlying the periodic system.
The fruit of human hands or a natural phenomenon?
The phenomenon of radiation actually always existed. People from the very beginning of their history lived in the environment of the so-called natural radioactive field. But radioactivity as evidence of the complex structure of the atom became a known phenomenon only at the beginning of the 20th century.
From space to the earth's surface comes part of the ionizing radiation. People are also irradiated from those sources 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, miners died en masse at the age of only 30-40 years on lead mines in Austria from the so-called mountain sickness. Local women married several times, as the mortality rate of miners exceeded the mortality rate of the common population by more than 50 times. Then such a technique as measuring radioactivity was not yet known. People could not even imagine that lead ores could contain hazardous uranium. Only in 1879 did doctors learn that “mountain sickness” was actually lung cancer.
The discovery of radioactive processes by Becquerel
At the end of the 19th century, studies were made, as a result of which radioactivity as evidence of the complex structure of atoms became apparent to society. In 1896, researcher A. A. Beckerel determined that substances containing uranium can lighten a photographic plate in the dark. Later, the scientist managed to find out that not only uranium has this property. Further, the Polish chemist Maria Skłodowska Curie, together with her husband Pierre Curie, discovered two new radionuclides: polonium and radium.
Becquerel’s experience itself was pretty straightforward. He took uranium salts, wrapped them in a dark colored cloth, and then exposed them to the sun to see how the energy accumulated by this substance would be re-emitted. But once a scientist noticed that the photographic plate begins to glow even when the uranium salts were not exposed to the sun. This led to the fact that radioactivity was discovered. Becquerel called the unknown rays X-rays (by analogy with the name X-rays).
Rutherford's experiences
Further, the English scientist Ernest Rutherford became interested in radioactivity . In 1899, he conducted an experiment to study this phenomenon. It consisted of the following. The scientist took uranium salt and placed it in a cylinder made of lead. Through a narrow hole, a stream of alpha particles fell onto 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. Rutherford then 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 Research
After all these experiments, radioactivity became known as evidence of the complex structure of atoms. After all, it turned out that it was the processes inside the nucleus of the atom that lead to such radiation. It is appropriate to recall here that since ancient Greece, the atom was considered an indivisible particle of the universe. The word "atom" itself meant "indivisible." As a result of research by scientists, people learned about spontaneous electromagnetic radiation, as well as about new particles of atoms - such a serious step forward physics took. 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.
Atom structure
Experimental studies have confirmed that the atom has a complex structure. It consists of a nucleus and negatively charged electrons. In 1932, domestic researchers D. Ivanenko and E. Gapon, as well as independently of them by the German physicist Heisenberg, proposed a model of the structure of the atom, called proton-neutron. According to this concept, an atom consists of particles called protons and neutrons. They are combined into a common group of nucleons.
Almost the entire mass of an atom is in its core. Protons, neutrons and electrons form a category of elementary particles. As a result of experimental studies, it was found that the serial number of the substance in the periodic system of elements is equal to the charge of its core.
Properties of radionuclides
To understand what radioactivity is and how it relates to the structure of the atomic nucleus, it is necessary to master a few simple terms. For example, radioactive isotopes are now called radionuclides. They differ from unstable in that they have different half-lives.
Radioactive isotopes, turning into other isotopes, become sources of ionizing radiation. Different radionuclides have varying degrees of instability. Some can decay over hundreds and thousands of years. Such radionuclides are called long-lived. All uranium isotopes can serve as an example. Short-lived radionuclides, in contrast, decay very quickly: within seconds, minutes or months.
What is radioactivity measured in?
The unit of radioactivity is 1 Becquerel. If one decay occurs in one second, then it is said that the activity of one or another isotope is equal to one Becquerel. Activity is that quantity which allows to evaluate the decay power arithmetically. Previously, scientists used another unit of radioactivity - Curie. The correlation between them is as follows: 1 billion accounts for 37 billion Bq.
In this case, it is necessary to distinguish between the activity of different amounts of a substance, for example, 1 kg and 1 mg. The activity of a certain amount of a substance 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 has become one of the most dangerous phenomena. Learning more about this phenomenon, people began to fear their consequences without reason. Many have the impression that gamma radiation can pose the greatest threat. But this is not entirely true, at least it does not threaten life. Irradiation with radiation is much more dangerous due to its penetrating ability. Of course, this indicator is higher for gamma rays than, for example, for 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. Exposure to ionizing radiation is determined using an absorbed dose indicator. But even this is not enough to assess the harm. After all, not every radiation is equally dangerous. The hazard coefficient of radiation is called weighting. The unit of radioactivity that is used to evaluate the radiation dose with a weighting factor is called the sievert.