What is radioactive decay?

Radioactive decay is defined as the spontaneous release of energy or particles from the nucleus of unstable atomic nuclei, which is characteristic of radioactive isotopes. This process occurs when an atom has an excess of energy or mass, leading to instability. During decay, the nucleus emits radiation in the form of alpha particles, beta particles, or gamma rays, and transforms into a different element or a different isotope of the same element.

The phenomenon is crucial in understanding nuclear reactions, radioactive dating, and the behavior of materials that contain radioactive isotopes. This spontaneous process does not require external intervention and allows the atom to reach a more stable state over time.

The other options represent significant concepts in nuclear physics but do not accurately define radioactive decay. Gaining electrons and transformation into stable isotopes describe different atomic processes, while nuclear fusion involves the combination of atomic nuclei rather than the disintegration of an unstable nucleus.