Radioactive decay describes the spontaneous and random transformation of unstable nuclei into more stable ones by emitting radiation such as alpha, beta, or gamma particles. In this topic you examine the statistical nature of decay, where the likelihood of a nucleus decaying in a given time is constant, leading to an exponential decrease in the number of undecayed nuclei. You work with key quantities such as activity, decay constant, and half-life, and learn how to model decay processes mathematically. You also look at how different types of radiation interact with matter and how decay chains form as nuclei transform through a series of steps. These ideas are central to understanding nuclear physics, dating techniques, radiation hazards, and applications in medicine and industry.

Nuclear energy refers to the energy released when changes occur in the nuclei of atoms, either through fission, where a heavy nucleus splits into smaller ones, or fusion, where light nuclei combine to form a heavier nucleus. In this topic you examine how mass and energy are related through E= m c squared, allowing small changes in mass during nuclear reactions to produce large amounts of energy. You study binding energy curves to understand why some nuclei release energy when they split while others release it when they fuse, and you compare the energy scales of nuclear processes with those of chemical reactions. You also look at practical applications such as nuclear power generation, alongside considerations of reactor design, fuel use, and waste management. Understanding nuclear energy provides the basis for analysing both natural and engineered nuclear systems.