WordNet sense 1 (syndrome resulting from exposure to ionizing radiation (e.g., exposure to radioactive chemicals or to nuclear explosions); low doses cause diarrhea and nausea and vomiting and sometimes loss of hair; greater exposure can cause sterility and cataracts and some forms of cancer and other diseases; severe exposure can cause death within hours):

radiation sickness, radiation syndrome

WordNet sense 2 (the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay):

radioactivity

WordNet sense 3 ((medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance):

irradiation, radiotherapy, actinotherapy, radiation therapy