After it was discovered that substances consist of molecules, and those, in turn, are made of atoms, a new question arose for physicists. It was necessary to establish the structure of atoms - what are they made of? E. Rutherford and his students undertook to solve this difficult task. The discovery of the proton and neutron by them took place at the beginning of the last century
E. Rutherford already had assumptions that the atom consists of a nucleus and electrons that revolve around it at a huge speed. But what the nucleus of an atom consists of was not entirely clear. E. Rutherford proposed the hypothesis that the composition of the atomic nucleus of any chemical element should be the nucleus of a hydrogen atom.
This hypothesis was later proved by a series of experiments, which resulted in the discovery of a proton. The essence of the experimental experiments of E. Rutherford was that nitrogen atoms were bombarded with alpha radiation, with the help of which some particles were knocked out of the atomic nucleus of nitrogen.
This process was recorded on a photosensitive film. However, the luminescence was so weak and the sensitivity of the film was also low, so E. Rutherford suggested that his students, before starting the experiment, spend several hours in a dark room so that their eyes could see subtle light signals.
In this experiment, using characteristic light traces, it was determined that the particles that were knocked out were the nuclei of hydrogen and oxygen atoms. The hypothesis of E. Rutherford, which led him to the fact that the discovery of the proton was completed, found its brilliant confirmation.
E. Rutherford proposed to call this particle a proton (in Greek, “protos” means the first). In this case, one must understand this so that the atomic nucleus of hydrogen has such a structure that only one proton is present in it. Thus was the discovery of the proton.
He has a positive electric charge. In this case, it is quantitatively equal to the charge of the electron, only the sign has the opposite. That is, it turns out that the proton and the electron balance each other, as it were. Therefore, all objects, since they consist of atoms, are not initially charged, and they receive an electric charge when an electric field begins to act on them. The structure of atomic nuclei of various chemical elements may contain a greater number of protons than in the atomic nucleus of hydrogen.
After the discovery of the proton was made, scientists began to understand that the nucleus of an atom of a chemical element consists not only of protons, because, conducting physical experiments with the nuclei of the beryllium atom, they found that the mass of protons in the nucleus was four units, while the total mass of the nucleus is nine units. It was logical to assume that another five units of mass belong to some unknown particles that do not have an electric charge, since otherwise the electron-proton balance would be violated.
James Chadwick, a student of E. Rutherford, conducted experiments and was able to detect elementary particles that emitted from the atomic nucleus of beryllium when they were bombarded with alpha radiation. It turned out that they do not have any electric charge. A lack of charge was discovered due to the fact that these particles did not respond to the electromagnetic field. Then it became clear that the missing element of the structure of the atomic nucleus was discovered.
This particle discovered by D. Chadwick was called a neutron. It turned out that it has the same mass as the proton, but, as already mentioned, it does not have any electric charge.
In addition, it was experimentally confirmed that the number of protons and neutrons is equal to the serial number of the chemical element in the periodic system.
In the Universe, one can observe such objects as neutron stars, which are often the final stage in the evolution of stars. Such neutron stars are very dense.