Your friend Paul says that the helium used to inflate balloons is a product of radioactive decay. Your mutual friend Steve says no way. Then there’s your friend Alison, who frets about living near a fission power plant. She wishes to get away from radiation by traveling to the high mountains and sleeping out at night on granite outcroppings. Still another friend, Michele, has journeyed to the mountain foothills to escape the effects of radioactivity altogether. While bathing in the warmth of a natural hot spring, she wonders aloud how the spring gets its heat. What do you tell these friends?