natural radioisotope
Technical term used in nuclear physics, chemistry, and environmental science. Refers to a radioactive isotope that occurs naturally, as opposed to one produced artificially.
Potassium-40, one of the natural radioisotopes, is widely present in rocks.
Natural radioisotopes were detected in the groundwater of this area.
Compound of 天然 (natural), 放射性 (radioactive), and 同位体 (isotope). The term is a direct calque from English 'natural radioisotope'.