This depends on several factors, including how many neutrons are produced in an average fission and how easy it is to make a particular type of nuclide fission.Ī chain reaction can have runaway results. The self-sustained fission of nuclei is commonly referred to as a chain reaction, as shown in Figure 22.27.įigure 22.27 A chain reaction can produce self-sustained fission if each fission produces enough neutrons to induce at least one more fission. Both factors affect critical mass, which is smallest for 239Pu. In particular, 235U and 239Pu are easier to fission than the much more abundant 238U. Additionally, some nuclides are easier to make fission than others. Some nuclides, such as 239Pu, produce more neutrons per fission than others, such as 235U. The minimum amount necessary for self-sustained fission of a given nuclide is called its critical mass. We can enhance the number of fissions produced by neutrons by having a large amount of fissionable material as well as a neutron reflector. Some neutrons escape the fissionable material, while others interact with a nucleus without making it split. However, not every neutron produced by fission induces further fission. It is analogous to a dense shield or neutron reflector directing neutrons back to interact with more other nuclei and perpetuate the fission chain reaction. Explain that if the plastic box were not there, the uncontrolled chain reaction would likely not occur. Good videos of a ping-pong ball dropped into a room full of ping-pong balls and mousetraps elucidate this idea very well and can be easily found online. At this point, it is a good idea to show a quick video of a chain reaction model. The catalyst typically occurs in the form of a free neutron, projected directly at the nucleus of a high-mass atom. As a result, a physical catalyst is necessary to produce useful energy through nuclear fission. And although it is true that huge amounts of energy can be released, considerable effort is needed to do so in practice.Īn unstable atom will naturally decay, but it may take millions of years to do so. Given that it requires great energy separate two nucleons, it may come as a surprise to learn that splitting a nucleus can release vast potential energy. In simplest terms, nuclear fission is the splitting of an atomic bond. Through two distinct methods, humankind has discovered multiple ways of manipulating the atom to release its internal energy. Knowing that energy can be emitted in various forms of nuclear change, is it possible to create a nuclear reaction through our own intervention? The answer to this question is yes. This section delves into a less-natural process. Without human intervention, some nuclei will change composition in order to achieve a stable equilibrium. So the answer to the question “Which of the following statements correctly contrasts nuclear fusion and nuclear fission?” is (A) in nuclear fission, large nuclei split, while in nuclear fusion, small nuclei combine.The previous section dealt with naturally occurring nuclear decay. This means that the splitting of large nuclei must be nuclear fission. During the combination of two small nuclei, the nuclei are fused together. But we need to know which one is fission and which one is fusion. So we have seen how large nuclei split and how small nuclei combine. The combination of two hydrogen nuclei to form helium occurs in the Sun. Combining nuclei requires much higher temperatures than splitting nuclei. It will also release three neutrons and nuclear energy.Īn example of two nuclei combining is the combination of two hydrogen nuclei to form a helium nucleus and nuclear energy. As uranium-236 is unstable, it will split into two smaller nuclei such as barium and krypton. Uranium-236 can be formed by bombarding uranium-235 with slow-moving neutrons. Uranium-236 is an example of an unstable isotope. Large nuclei split when they are unstable. We can see from options (A) and (B) that one of these processes involves large nuclei splitting and the other involves small nuclei combining. Nuclear fusion and nuclear fission are both processes which release a lot of energy. Or (B) in nuclear fusion, large nuclei split, while in nuclear fission, small nuclei combine. Which of the following statements correctly contrasts nuclear fusion and nuclear fission? (A) In nuclear fission, large nuclei split, while in nuclear fusion, small nuclei combine.
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