For example, this can occur when the shape of the nucleus undergoes a change.
Neither the mass number nor the atomic number is changed when a nucleus emits a The time required for half of the atoms in any given quantity of a radioactive isotope to decay is the half-life of that isotope. For example, the half-life of C is 5730 years, thus it is useful for dating archaeological material.
As in chemical reactions, nuclear reactions can either be exothermic (i.e. Fusion is a nuclear process in which two light nuclei combine to form a single heavier nucleus.
Because the reacting nuclei are both positively charged, there is a large electrostatic repulsion between them as they come together.
Only when they are squeezed very close to one another do they feel the strong nuclear force, which can overcome the electrostatic repulsion and cause them to fuse.
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