When nuclear energy is mentioned, many people may think of nuclear power, radiation, or even related safety issues. To further understand these topics, it is necessary to first understand radioactive decay, nuclear fission, and nuclear fusion. All three involve changes in atomic nuclei, and may be accompanied by the release of radiation. However, the processes, radiation released, and applications differ among them.

During the process of radioactive decay, an unstable atomic nucleus radiates particles and energy to decay into a more stable nucleus. This process occurs spontaneously and randomly; it requires no external force to trigger it, nor can its occurrence be controlled. The radiation emitted during radioactive decay can be in the form of α particles, β particles, γ rays, or neutrons. In a given sample, as unstable nuclei decay into more stable ones, the number of unstable nuclei gradually decreases. Consequently, the frequency of nuclear decay decreases, and the amount of radiation released slowly diminishes over time.

Nuclear fission refers to the process where a heavy atomic nucleus splits into two or more lighter nuclei. The energy released by nuclear fission is in general higher, and this energy is released in the form of γ rays or neutrons.

Nuclear fission is a vital component in nuclear power plants for converting nuclear energy into electricity. However, nuclear fission rarely occurs spontaneously. In nuclear power plants, neutrons are used to bombard heavy atomic nuclei and induce fission. The neutrons released during nuclear fission can then cause other nuclei to split. By controlling the number of neutrons, their absorption, and reactor conditions, the stability of the fission chain reaction can be maintained.

Nuclear fusion is the process in which two or more atomic nuclei combine to form a single, larger atomic nucleus. This process generally releases a massive amount of energy, and this energy is also released in the form of γ rays or neutrons.

Nuclear fusion is the energy source of the Sun and other Stars. One key difference between nuclear fusion and nuclear fission is that fusion usually does not produce as much long-lasting radioactive material as nuclear fission does, so it may pose a lower long-term radioactive risk. However, because atomic nuclei all carry positive electric charge, they repel one another. To make nuclear fusion happen, extremely high temperatures and appropriate confinement conditions are typically required. Scientists are currently researching how to stably control nuclear fusion and are attempting to develop it as a cleaner energy source.

In conclusion, although radioactive decay, nuclear fission, and nuclear fusion all involve changes in atomic nuclei, there are clear differences among the three in terms of the occurrence processes, radiation released, and practical applications. Radioactive decay is a naturally occurring process; nuclear fission has been applied to nuclear power generation; nuclear fusion remains a direction of research for future energy usage.