Radioactive isotopes are variants of chemical elements that have unstable nuclei, leading them to emit radiation as they decay into more stable forms. This process can involve the release of particles or electromagnetic waves, which can be detected and measured. Common examples include carbon-14, used in dating ancient organic materials, and uranium-238, which is important in nuclear energy production. These isotopes can occur naturally or be artificially produced in laboratories. They have various applications in fields such as medicine, where they are used in radiotherapy to treat cancer, and in nuclear medicine for diagnostic imaging.