Radioactivity is the spontaneous disintegration of unstable atomic nuclei, which lose energy by emitting radiation (particles or electromagnetic waves) to become more stable atoms. This process is random but follows predictable rates, measured by the half-life, and results in radioactive decay, producing different types of radiation like alpha, beta, and gamma rays. What Causes Radioactivity? Unstable Nuclei: Atoms with an unstable nucleus, due to an imbalance of protons and neutrons or excess i