Sigh It has to do with dilution, and half life especially of the heavy stuff Just because something has trace amounts doesn't mean it'll kill you Radiation isn't like arsenic or any classical poison or venom people might associate with "bad matter" at the subconcious It works closer to heat Think of it like, you can only absorb so much before you are "burned" if you will, i. E. You are past the point of your body's healing index to fix the dna damage Douching the elephants foot at chernobyl would be like touching lava. It's very unpleasant and you're probably going to die. On the other hand, If non radioactive normal matter is "frozen" or "freezing" by my analogy, then a glass of reactor coolant water is room temperature compared to the freezing non radioactive matter, by comparison, or the blazing hot uranium rods, again my use of hot and cold in this context only extends to the damage the ionizing radiation can do to you, since heat is a type of radiation, we can use our imagination to "play-doh" with existing concepts to understand more esoteric and invisible ones. Makes sense? I'm trying hard to ELI5 nuclear physics here lmao