What term describes the phenomenon where substances spontaneously emit radiation?

The phenomenon where substances spontaneously emit radiation is known as radioactivity. This process occurs when unstable atomic nuclei release energy in the form of particles or electromagnetic waves. This emission can happen in various forms, including alpha particles, beta particles, or gamma rays, and is a natural occurrence in certain elements, such as uranium and radium.

Radioactivity is a fundamental concept in nuclear physics and chemistry, illustrating the inherent instability of certain isotopes. As these isotopes seek a more stable configuration, they undergo transformations that lead to the emission of radiation. Understanding radioactivity is crucial for fields such as medicine, energy production, and understanding natural processes in the environment.

Ionization refers to the process of removing electrons from atoms, while decay generally pertains to the specific types of transformations that unstable isotopes undergo during radioactive decay but does not encompass the broader definition of spontaneous emission. Radiation exposure indicates the amount of radiation that comes into contact with an object or person, but does not specifically define the phenomenon of emission itself.