放射性衰变/ 放射性衰變 fàngshèxìngshuāibiàn radioactive decay
The process by which certain unstable elements spontaneously release radiation to transform into more stable elements; also called 衰变 shuāibiàn (shuāibiàn) or 放射衰变 fàngshèshuāibiàn (fàngshè shuāibiàn)