Define "radioactive decay".

Radioactive decay is defined as the process by which an unstable atomic nucleus loses energy by emitting radiation. This can occur in various forms, such as alpha decay, beta decay, or gamma decay, each involving the release of particles or electromagnetic waves. The decay continues until the nucleus reaches a stable state, resulting in the transformation into a different element or isotope.

This definition highlights the fundamental concept of radioactivity, where a nucleus that is not in a stable configuration undergoes a transformation to achieve stability, releasing energy in the form of radiation in the process. Understanding radioactive decay is crucial in the context of nuclear physics and nuclear power generation, as it explains how nuclear reactions provide energy. This relationship is essential for the safe management of nuclear materials and the operation of reactors.

The other choices do not accurately describe radioactive decay. The process of nuclear fuel storage involves the physical containment of fuel and does not pertain to the emission of radiation. Enhancing nuclear reactor output relates to optimization and efficiency rather than the inherent properties of unstable nuclei. Cooling down reactors refers to post-operation safety procedures, unrelated to the atomic changes involved in decay processes.