Which iodine protects again liver damage if you are exposed to radiation?

I read some years ago that iodine does this. I have potium iodide and Lugol's iodine. Does either of these protect your liver from damage from radiation exposure? I know how to use Lugol's, but I've lost the instructions for the potium iodide. (I bought it 10 years ago when I read about this.) If neither of these is the right iodine, which one is and how do I use it?