Natural radiation arises from many sources, from the unstable atoms within our own bodies and in the materials around us, from the Sun, and even from beyond the Solar System. Additional sources include the legacy of testing nuclear weapons, nuclear waste, and nuclear accidents. All these sources have provided means of dating environmental materials and tracing the movements of substances through land, sea, and air. But ionising radiation also interacts with DNA, which has led to a remarkable range of studies to examine how and how quickly these unstable atoms are accumulated by both humans...