Radioactivity: release of trapped Radon or some other radioactive product where the apparent half-life is in fact dispersal. Arguments about radioactivity from Radon ave very complex because we have a chain of transmutations in which radioactive intermediates of different life-times can build up, so that activity measures at equilibrium have both physical and nuclear components.
Although everything here might be true, there is an additional worm in this can that has been opened up: we might be seeing activity that is induced, above and beyond what natural activity there already ways. I do not know how this hypothesis might be tested in the present context, given all of the variables.