"Nowadays you wouldn't want to do that voluntarily, and you wouldn't want to do it without understanding the consequences, but there are some situations that you might want to do it in... [T]here's a very good reason for that, because if you take a much lower energy beam that the Large Hadron Collider beam, and you put it into water, or into the human body, or into tissue and you start it with the correct amount of energy, it will actually slow down and stop, and deposit almost all of its dose (or its energy) in one spot... [W]e call this the ."