decaythe spontaneous breakdown of an unstable atomic nucleus into smaller partsThe rate of radioactive decay is measured using half-lives, which vary enormously between different isotopes.NoteThe rate of radioactive decay is measured using half-lives, which vary enormously between different isotopes.Elon.io is an online learning platformWe have an entire course teaching TOEFL Academic Vocabulary grammar and vocabulary.Start learning TOEFL Academic Vocabulary now