What is Nuclear Fission?

Nuclear fission, also known as nuclear fission, refers to a form of nuclear reaction in which a heavy atomic nucleus (mainly a uranium or thorium nucleus) is split into two or more smaller mass atoms. The source of energy for an atomic bomb or nuclear power plant is nuclear fission. Among them, uranium fission is the most common in nuclear power plants. After thermal neutrons bombard uranium-235 atoms, they will emit 2 to 4 neutrons, which then strike other uranium-235 atoms to form a chain reaction.

Nuclear fission, also known as nuclear fission, is a

Fission release energy is related to the way mass-energy is stored in the nucleus. From the heaviest element to iron,

From the viewpoint of the droplet model, the whole process of fission is briefly described below.

The ground state energy of a stable heavy nucleus is always lower than the fission barrier. To cross the barrier, fission can occur. The nucleus in the ground state can pass quantum mechanics.

The nuclei generated by heavy nuclei during fission are called fission fragments before the release of instant neutrons, and the nuclei after the release of instant neutrons are called fission products. Fission products can be divided into primary fission products without beta decay and Secondary fission products that undergo more than one beta decay. Beta decay does not affect the mass of the nucleus, so it is not necessary to distinguish between the two cases when discussing the mass of fission products.

Can be determined experimentally using the following methods

Emitted when the nuclear fission

There is no comprehensive and unified theory about the whole phenomenon of fission, but some mature theoretical models have been developed about various aspects of fission.

Calculation of fission potential energy surface

The original method was to apply the droplet model. That is, the nucleus is regarded as a uniformly charged incompressible droplet, and a variety of deformation parameters are used to describe the various shapes of the nucleus. In principle, the potential energy under various deformations can be calculated. In the resulting potential energy surface (

The study of fission has been an active branch of nuclear physics for decades. This is because:

Fission has great practical value;

Fission is a very complex nuclear process. Studying this process is helpful

Nuclear fission was discovered in 1938. Due to the needs of World War II at the time, nuclear fission was first used to make a powerful atomic weapon, the atomic bomb. The immense power of the atomic bomb is the tremendous energy generated by nuclear fission. In addition to using nuclear fission for the production of atomic bombs, people are working harder to study the huge energy generated by nuclear fission for the benefit of mankind, so that nuclear fission is always performed under people's control. Nuclear power plants are such devices

Focus on nuclear fission (8 photos)

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In 1934, E. Fermi and others irradiated uranium with neutrons in an attempt to capture neutrons by uranium nuclei and then undergo beta decay to transuranic elements with an atomic number of 93 or higher, which attracted the attention of many chemists. in

Many people did this kind of experiment from 1934 to 1938, but different researchers got different results. Some claimed to have discovered transuranic elements, while others said that radium and thorium were obtained.

In 1938, O. Hahn and F. Strassman conducted a series of rigorous chemical experiments to identify these radioactive products, and concluded that the so-called radium and thorium are actually lanthanum and barium with atomic weights much smaller than them. This phenomenon can only be explained by assuming that the nucleus is split into two or more pieces. This process of division is called fission.

In 1939, L. Meitner and OR Frisch first suggested the use of splitting of charged droplets to explain fission. In the same year, N. Bohr and JA Wheeler systematically studied the fission process of the nucleus on the basis of the nuclear droplet model and statistical theory, which laid the foundation for the fission theory.

In 1940, KA Petrozac and .. Flierov observed that uranium nuclei would undergo fission on their own, and found a new way of radioactive decay-spontaneous fission.

In 1947, Qian Sanqiang et al. Discovered the trisomy (that is, it was divided into three fragments, and the third could be alpha particles or fragments with similar mass to the other two fragments).

In 1955, A. Bohr put forward the concept of fission track based on the collective model of atomic nuclei, taking the theory of fission a step further. In 1962, .. Polikanov and others discovered a spontaneous fission homogeneity state.

In 1967, BM Strugginsky proposed a "macro-micro" method based on the shell model based on the droplet model, and derived the bimodal fission barrier, which is another new achievement in the history of fission research.