The best replacement for stable isotopes is radioisotopes.

The best alternatives to stable isotopes are rated as following:
★★★★★  radioisotopes
★★★★  radioactive isotopes
★★  unstable

Your alternative for stable isotopes is not listed? Suggest!
Speaking about stable isotopes, one probably shouldn't forget about elements.

Other search terms related to stable isotopes and their ratings are:
★★★★★ elements
You have in mind a companion for stable isotopes and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of stable isotopes in all years. Click on graph for more.
stable isotopes
radioisotopes
radioactive isotopes