Duude i really like your game, but i couldn't figure out how to continue in radiation... all this game is scrolling down, why the heck did you chose to implement a side scroller there?
Radiation is just max everything out & get to level 700. You'll need to upgrade 2nd ring a decent bit as well as dive into Abyss D to make it to level 700, where you'll unlock infinity, the final (currently) bit of content in the game.
If you're confused on how to get mutagens, just read the info section of the game.