What term means one element changing into another during radioactive decay?

The term for one element changing into another during radioactive decay is transmutation.

In radioactive transmutation, an unstable atomic nucleus changes into a different nucleus. Because an element’s identity is determined by its number of protons, a change in atomic number creates a new element. The process may release alpha particles, beta particles or gamma radiation, depending on the decay pathway.

For example, alpha decay lowers the parent nucleus’s atomic number by two and its mass number by four. In beta-minus decay, the atomic number rises by one while the mass number remains unchanged. These changes helped Rutherford and Frederick Soddy establish that radioactive atoms were transforming into other elements.

Transmutation is not the same as fission. Fission splits a heavy nucleus into smaller nuclei, while transmutation is the broader idea of one nuclide or element becoming another, whether through natural radioactive decay or an induced nuclear reaction. Ionization only removes or adds electrons and does not change the element.