Synonyms for Irradiation (same or very similar meaning)
WordNet sense 1 (a column of light (as from a beacon)):
beam, ray, shaft, beam of light, light beam, ray of light, shaft of lightWordNet sense 2 ((medicine) the treatment of disease (especially cancer) by exposure to a radioactive substance):
radiation, radiotherapy, actinotherapy, radiation therapyFrom the ODE community, based on WordNetadd/edit