noun
radioisotope; radioactive isotope
Technical term in physics; refers to an isotope that emits radiation.
放射性同位体は医療や工業で利用されている。
Radioisotopes are used in medicine and industry.
同位体 means 'isotope' in general, while 放射性同位体 specifically refers to a radioactive isotope.
Compound of 放射性 (radioactivity) + 同位体 (isotope).