Complex sentence: Asimov returned to the radioactive Earth theme in The Stars Like Dust, The Currents of Space, "Foundation and Earth", and he would explore it most fully in "Robots and Empire".
Split into simpler sentences: Asimov returned to the radioactive Earth theme in "The Stars Like Dust", "The Currents of Space" and "Foundation and Earth". He would explore it most fully in "Robots and Empire".