Radioactive material refers to any substance that emits radiation as a result of its atomic structure. This type of material is typically unstable and can undergo decay, releasing particles or energy in the process. Radioactivity occurs when an atom's nucleus has an excess of protons or neutrons, causing it to be unstable and emit radiation until it reaches a stable state. The emission of radiation can take many forms including alpha particles, beta particles, gamma rays, or X-rays. Depending on the type and amount of radiation emitted, radioactive materials may pose varying levels of risk to humans and the environment.