Radioactivity is an exclusively natural property and cannot be created artificially.

The first radioactive substances were discovered in nature. Uranium, radium, and related materials emitted radiation spontaneously, so radioactivity initially looked like an intrinsic property belonging to a special set of naturally unstable substances.

In 1934, Irène Joliot-Curie and Frédéric Joliot bombarded light elements with alpha particles and found something new: after the external source was removed, the target material continued emitting radiation.

The bombardment had created unstable nuclei that did not previously exist in the sample. Artificial radioactivity had been produced.

The discovery rapidly expanded nuclear physics. Artificial radionuclides could be generated for tracing chemical and biological processes, medical diagnosis and therapy, industrial measurement, and later many other applications.

Artificial radioactivity does not mean any object becomes permanently radioactive after arbitrary exposure. Induced activity depends on the specific nuclear reaction, target nucleus, projectile energy, and half-life of the resulting isotope.

The conceptual shift was that radioactivity was not limited to a fixed list of substances supplied by nature. Unstable nuclei could be manufactured.