Isotope and Radioisotope

Isotope noun - One of two or more atoms with the same atomic number but with different numbers of neutrons.

Radioisotope and isotope are semantically related. In some cases you can replace term "Radioisotope" with "Isotope", this nouns are similar.

Radioisotope noun - A radioactive isotope of an element; produced either naturally or artificially.

Isotope and radioisotope are semantically related. You can use "Isotope" instead a noun "Radioisotope".