Nuclear fission, also known as nuclear fission, is a form of nuclear reaction in which a nucleus splits into several nuclei. It refers to a form of nuclear reaction in which heavy atoms, mainly uranium or plutonium, splits into lighter atoms.

Only some very large atomic nuclei such as uranium (yóu), thorium (tǔ), etc. can undergo nuclear fission. After absorbing a neutron, the nucleus of these atoms will split into two or more nuclei with smaller mass, and at the same time release two to three neutrons and a large amount of energy, which can cause other nuclei to undergo nuclear fission..., making the process continue, and this process is called chain reaction. When a nucleus undergoes nuclear fission, the release of huge energy is called atomic energy, commonly known as atomic energy. The fission of all nuclei of 1 kilogram of uranium-235 will generate 20,000 megawatt hours of energy (enough to allow a 20 megawatt power plant to operate for 1,000 hours), which is as much energy as burning 3 million tons of coal. See also fission and fusion.

Nuclear fission was discovered in 1938. Due to the needs of World War II at that time, nuclear fission was first used to create a powerful atomic weapon - atomic bomb. The huge power of the atomic bomb comes from the huge energy generated by nuclear fission. At present, in addition to using nuclear fission to create atomic bombs, people have worked harder to study the use of the huge energy generated by nuclear fission to benefit mankind, so that nuclear fission will always be carried out under people's control. Nuclear power plants are such devices.

Fission releases energy because the storage method of mass-energy in the nucleus is the most effective in the form of the nucleus of iron and related elements (see Nuclear Synthesis). From the heaviest element to iron, the energy storage efficiency is basically continuously changing, so any process in which heavy nucleus can split into lighter nucleus (to iron) is beneficial in energy relations. If the nucleus of heavier elements can split and form lighter nucleus, energy will be released. However, once the nucleus of many such heavy elements is formed inside the star, even if it requires input energy during formation (taken from supernova explosions), they are very stable. Unstable heavy nucleus, such as the nucleus of uranium-235, can spontaneously fission. Fast moving neutrons can also trigger fission when impacting unstable nucleus. Because fission itself releases

The split neutrons in the nuclear, so if a sufficient amount of radioactive material (such as uranium-235) is piled together, the spontaneous fission of one nuclear will trigger the fission of two or more nuclei near each other, each of which triggers the fission of at least two other nuclei, and so on, the so-called chain reaction occurs. This is the energy release process called the atomic bomb (actually a nuclear bomb) and the nuclear reactor used for power generation (through a controlled slow method). For nuclear bombs, chain reaction is an out-of-control explosion because the fission of each nuclear causes fission of several other nuclei. For nuclear reactors, the rate of reaction is controlled by the absorbable part of the neutron inserted into the uranium (or other radioactive material) reservoir, so that on average, the fission of each nuclear just triggers the fission of the other nuclei.

The high-energy neutrons released by nuclear fission move extremely high (fast neutrons), so they must be slowed down to increase their chances of impacting atoms and trigger more nuclear fission. Generally, commercial nuclear reactors use slower agents to slow down the high-energy neutrons and turn them into low-energy neutrons (hot neutrons). Commercial nuclear reactors generally use ordinary water, graphite and more expensive heavy water as slower agents.

Nuclear fission is the change in which a nucleus splits into several nuclei. Only some nuclei with very large mass, such as uranium, thorium, etc., can nuclear fission occur. After absorbing a neutron, the nucleus of these atoms will split into two or more nuclei with smaller mass, and at the same time releases two to three neutrons and a large amount of energy, which can cause other nuclei to undergo nuclear fission..., making the process continue, and this process is called chain reaction. When a nucleus undergoes nuclear fission, the release of huge energy is called atomic energy, commonly known as atomic energy. 1 grams of uranium 235

The energy released after complete nuclear fission is equivalent to the energy generated by burning 2.5 tons of coal. A nuclear weapon that is more powerful than an atomic bomb is a hydrogen bomb, which uses nuclear fusion to play a role. The process of nuclear fusion is the process of polymerizing several atomic nuclei into one atomic nucleus. Only lighter atomic nuclei can undergo nuclear fusion, such as deuterium, tritium, the hydrogen isotopes. Nuclear fusion will also emit huge energy, and it will be greater than the energy released by nuclear fission. The sun continues to fusion into helium, and its light and heat are generated by nuclear fusion.

How was nuclear fission discovered?

Lise Meitner and Otto Hahn are both researchers at the Kaiser Wilhelm Institute in Berlin, Germany. As part of the research on radioactive elements, Meitner and Hahn have worked hard for many years to create atoms heavier than uranium (transuranium atoms). Bombing uranium atoms with free protons, some protons will hit the uranium nucleus and stick to it, thus producing elements heavier than uranium. This seems obvious, but has not been successful.

They tested their methods with other heavy metals, and each reaction was unexpected, everything happened as described by Lizer's physical equation. But once uranium came, the heaviest element that people knew, would not work. Throughout the 1930s, no one could explain why experiments with uranium always failed.

Physically speaking, it makes no sense that atoms heavier than uranium cannot exist. However, more than 100 experiments have not succeeded in one success. Obviously, something they did not realize during the experiment. They needed new experiments to illustrate what exactly happened when free protons bombarded the uranium nucleus.

Finally, Odog thought of a way: use non-radioactive barium as a mark to continuously detect and measure the existence of radioactive radium. If uranium decays into radium, barium will be detected.

They conducted previous experiments to determine the reaction of barium to radioactive radium in the presence of uranium, and also remeasured the exact decay rate and decay pattern of radium. This took them three months.

Before they could conduct substantive experiments, Lizer had to flee to Sweden to avoid the Hitler Nazi Party that came to power. Odo had to conduct their great experiments alone.

Two weeks after Hahn completed the experiment, Lizer received a long report, which described the failure of his experiment. Hahn bombarded uranium with a clustered particle flow, but he did not even get radium. He only detected more barium - barium was far more than the amount at the beginning of the experiment. He was puzzled and asked Lizer to help him explain what was going on.

A week later, Lizer was walking in the snowshoes in early winter, and this was a scene that flashed through her heart: atoms tear themselves apart. The picture came so vivid, amazing and intense that she could almost feel the nucleus beating from her imagination, and could hear the hissing sound when the atoms tear apart.

She immediately realized that she had found the answer: the increase in protons made the uranium nucleus very unstable, and thus split. They conducted another experiment to prove that when free protons bombarded radioactive uranium, each uranium atom split into two parts, generating barium and krypton. This process also released huge energy.

In this way, Meitner discovered the process of nuclear fission.

Nearly four years later, at 2:20 pm on December 2, 1942, Enrique Fermi turned the switch, and hundreds of cadmium control rods absorbing neutrons rushed out of the reactor made of graphite blocks and tons of uranium oxide balls. Fermi stacked 42,000 graphite blocks in the underground tennis court under the west stands at the University of Chicago Stadium. This was the world's first nuclear reactor - the product of Metner's discovery. In 1945, the invention of the atomic bomb was the second application of her nuclear fission discovery.
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