For this you need two people to do this glitch.

Create a class with marathon lightweight and a sub machine gun painkiller and a tactical insertion.

You and your friend go to a spot where there is radiation.

You lay down a tactical insertion, just before the radiation get your friend to shoot you until you get painkiller and as soon as you get it you run into the radiation and then you will soon stop getting hurt.

You will also be out the map.