conversion of one chemical element or an isotope into another chemical element

Transmutation is a basic process in alchemy. The most important form of transmutation is the change of lead into gold. Alchemists tried and failed to change base metals (metals of very little value) into a metal of high value like gold.

However, more recent work by James Chadwick and Irène Joliot-Curie in nuclear physics has established that radioactivity does lead to elemental changes.