Nuclear reactions are processes where the nucleus of an atom changes, resulting in the release or absorption of energy. These reactions can occur in various ways, such as through fission, where a heavy nucleus splits into smaller nuclei, or fusion, where light nuclei combine to form a heavier nucleus. Both processes are fundamental to the energy produced in nuclear power plants and the reactions that power the sun. In addition to energy production, nuclear reactions are also important in medical applications, such as radiation therapy for cancer treatment. They can also create new elements through transmutation, which occurs in laboratories or during supernova explosions in space. Understanding these reactions helps scientists harness their power for various uses.