They realized that this made possible a chain reaction with an unprecedented energy yield. Meitner and Frisch carried out further experiments, which showed that the U-235 fission could release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). She was the first to realize that Hahn’s barium and other lighter products from the neutron bombardment experiments were coming from the fission of U-235. When they finally published the results in 1939, they came to the attention of Lise Meitner, an Austrian-born physicist who had worked with Hahn on his nuclear experiments. When they finally identified one of the products as Barium-141, they were circumspective of publishing the finding because it was unexpected. Rather than the heavy elements they expected, they got several unidentified products. They attempted to create transuranic elements by bombarding uranium with neutrons. Nuclear fission of heavy elements was discovered on December 17, 1938, by Otto Hahn and his assistant Fritz Strassmann. The reactor core consists of nuclear fuel, control rods, moderator (coolant), and neutron reflectors. Physics design of nuclear reactors entails two main aspects, namely, theoretical simulations and their experimental validation.The fission takes place in the nuclear reactor core.The multiplication factor is also influenced by other parameters such as temperature, fuel burnup, and reactor poisoning.Insertion of the rods decreases the parameter one or more (multiplication factor), thus decreasing the power.In a hydrogen bomb, two isotopes of hydrogen, deuterium and tritium are fused to form a nucleus of helium and a neutron. Withdrawal of the rods increases the parameter one or more (multiplication factor), thus increasing the power. The power that fuels the sun and the stars is nuclear fusion.Control rods contain material that absorbs neutrons ( boron, cadmium, …).The consequence of fission or fusion is the absorption or release of energy. For reactors using light water as a moderator, enriched uranium fuel is required. Fission is the splitting of a heavy nucleus into lighter nuclei and fusion is the combining of nuclei to form a bigger and heavier nucleus.Therefore the moderator is used to slow down neutrons (to increase the probability of fission). The probability that fission will occur depends on incident neutron energy.The chain reaction means if the reaction induces one or more reactions.The fission process produces free neutrons (2 or 3).Most of the energy (~85%) is released in the form of the kinetic energy of the split parts.Nuclear fission is the main process of generating nuclear energy.
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