From Big Medical Encyclopedia

NUCLEAR REACTIONS — the transformations of atomic nuclei caused by impact on them of elementary particles or other kernels.

As a result I. river transformation of one chemical element into another is possible. I. rubles are used for receiving the isotopes (see) which are widely applied in the industry and medicine. Work of nuclear power plants is based on fission tests of kernels of uranium and plutonium (see nuclear reactors). I. rubles are used in nuclear physics for studying of a structure and properties of an atomic nucleus (see an atomic nucleus) and elementary particles (see).

For receiving I. rubles of an atomic nucleus bombard the particles moving with high speeds. Such particles arise at radioactive decay (see Radioactivity), they are available as a part of space radiation (see), and also can be received by means of particle accelerators (see). Only one of many thousands of particles bombarding substance causes I. the river, energy of the others is spent for ionization of atoms and other processes. For particles of high energy and neutrons this indicator can be much higher. For allocation of products I. rubles use methods of radiochemistry. I can also cause heating of substance to temperatures taken by millions of degrees. river. Such reactions received the name of thermonuclear.

The first I. the river is carried out in 1919 by E. Rutherford, to-ry during the bombing by alpha particles of kernels of nitrogen received kernels of oxygen and a proton:

14N + >and-170 + r ili14ya (and, p) 1? 0

7 8 7 8

reactions Of this kind are usually written down in the reduced form: And + and —> In + in or And (and, c) in, where And — an initial kernel, and — a bombarding particle, In — a final kernel, in — the taking-off particle (them maybe a little).

In a crust, time several thousands I are known. river. Mechanism Ya. river — complex process of reorganization of an atomic nucleus. It is supposed that at I. the river occurs education, and then disintegration of the compound nucleus which is turning out at absorption by an initial kernel of a bombarding particle in the beginning. As well as chemical reactions, I. rubles can proceed as with absorption, and allocation of energy, and at I. the river is allocated to energy in millions times more, than at chemical reactions. Chain reactions of uranium fission or plutonium and synthetic reaction

of 235

easy kernels are of particular practical interest. At division 92 U

two splinters and 2 — 3 neutrons are formed. Everyone their these neutrons is capable to cause the new act of division, however, if the mass of uranium is small, many neutrons take off outside, without having managed to face the corresponding kernels. If the mass of the breaking-up uranium is more than certain critical size, then neutrons cause new acts of division, and the quantity of splinters and neutrons promptly increases that leads to explosion of huge force. This process happens at explosion of an atomic bomb (see. Nuclear weapon). If to create such conditions that only one of the neutrons which are formed at uranium fission will cause the new act of division, then quantity of the kernels sharing at every moment will be approximately same, explosion will not happen, and the marked-out heat can be used for receiving the electric power (1 g of uranium gives the same amount of energy as 2,5 t of coal). Work of nuclear power plants is based on it. A bigger amount of energy is emitted at synthetic reactions of easy kernels, however such reactions proceed at very high temperatures (many millions of degrees). Action of a hydrogen bomb is based on synthetic reaction of helium nuclei from kernels of a deuterium and hyzone. Temperature, necessary to start this reaction, is provided with explosion of an atomic bomb, edges are carried out by a role of a peculiar fuse. It is not possible to make synthetic reaction of easy kernels managed yet, but in this direction intensive scientific research as in - our country, and abroad is conducted. The managed thermonuclear reaction will allow to provide mankind with almost inexhaustible energy source.

Bibliography: Bourne M. Atomic physics, the lane with English, M., 1965; Kukhling of X. The reference book on physics, the lane with it., page 427, M., 1982; Works of the International conference on the chosen questions of structure of a kernel, t. 2, page 45, Dubna, 1976; Shirokov Yu. M. and Yudin N. P. Nuclear physics, page 113, M., 1980; Shpol-

with to and y E. V. Atomic physics, t. 1 — 2 * M., 1984.