Thus (5) can also be rewritten as (7).

If the reaction yield is greater than zero, then this reaction is exo-energetic and is accompanied by the release of energy into the kinetic energy of the reaction products, in the opposite case – absorption and is called endo-energetic. The adjustment of such a process becomes clear both by the mass difference before and after the reaction, and with a positive difference, we can say that it turns into kinetic energy and the reaction generates energy, in the opposite case, that is, with a negative difference, the process absorbs it.

The law of conservation of momentum also applies, which is very noticeable in direct reactions (8).

At the same time, there is a law of conservation of momentum and a number of other laws, but the most basic ones acting in the reaction are these two conservation laws.

But now it is important to focus on the types of nuclear reactions, and there are several of them: nuclear fission reaction, fusion, thermonuclear reaction and photonuclear reaction. The first type is a nuclear fission reaction, this is the process of splitting an atomic nucleus into two, and less often into three nuclei with close nuclear masses, which are called fission fragments. Other reaction products may also occur, including light nuclei – alpha particles, deuterons, as well as neutrons and gamma quanta. Fission itself is spontaneous and spontaneous, or forced, due to interaction with other particles, for example neutrons. The fission of heavy nuclei is in most cases an exo—energetic process, which makes it possible to obtain energy from radiation and kinetic energy of products from this process.

The nuclear fusion reaction is the second nuclear process, which consists in the fusion of two nuclei to form a new, heavier nucleus. This process is often accompanied by the emission of gamma rays or other elementary particles. Fusion of nuclei is most often an endo-energetic process, which most often requires the introduction of energy through the kinetic energies of particles in order to overcome the Coulomb barrier – the electrostatic repulsion of nuclei. The fusion of two nuclei and giving them energy can be realized, as it is not difficult to guess in charged particle accelerators, or these particles originally possessed this energy, for example, cosmic radiation particles, but there is another way – it is heating matter to extremely high temperatures in a special thermonuclear reactor, where the kinetic energy of particles and temperatures are extremely huge.

In this way, it is possible to approach thermonuclear reactions. In such reactions, the fusion of light nuclei leads to the conversion of the excess mass of the original nuclei into energy, since the total mass of the merged nuclei is greater than the mass of the resulting nucleus-the reaction product.

From this it can be concluded that the nuclear fusion reaction of the initial nuclei must have a relatively large kinetic energy, because they experience a rather powerful electrostatic repulsion when passing from their side of the Coulomb barrier. According to the molecular kinetic theory, their kinetic energy can be represented as the temperature of the entire substance, therefore heating will lead to an increase in the kinetic energy of the composite particles and their fusion. This is how nucleon synthesis develops in the bowels of stars with the formation of new nuclei under enormous temperatures.

In particular, the fusion reaction of protons and helium nuclei occurs in large quantities, and as a side result, other isotopes of substances are formed, including deuterium and tritium, as isotopes of hydrogen. And finally, the last type of nuclear reaction is a photonuclear reaction, in which case a gamma quantum is absorbed with sufficient energy to excite the nucleon composition, that is, the nucleus, so that it becomes composite, that is, it can be considered as such, and also releases a different structure from itself, or decays.