If you don't have the Immaculate Armor, there's a way you can still go down. You will be affected by radiation, but if you are a high level mage that won't be a problem. Put "Healing" in one of your hands and a weapon on another (so you can fight the enemies). Go down healing yourself non-stop. When you arrive at the bottom chamber, go through the door, it will load a screen, and then radiation won't affect you anymore.
:)