The aim of the course is to analyze the problems related to funds from radioactivity, in particular that originated by the decay of heavy isotopes, in the context of fundamental physics experiments, in particular underground ones dedicated to the search for rare events. The decay chains will be described, the main connected quantities will be redefined, some examples of which and how radioactive isotopes can produce an effect in fundamental physics detectors will be illustrated; and how these effects can be reduced or estimated.