Is it ensure, insure, or assure?
c.1600, "to cast beams of light upon," from Latin irradiatus, past participle of irradiare "shine forth," from assimilated form of in- "into, in" (see in- (2)) + radiare "to shine" (see radiate). Meaning "expose to radiation other than light" (originally X-rays) is from 1901. Related: Irradiated; irradiating.
irradiate ir·ra·di·ate (ĭ-rā'dē-āt')
v. ir·ra·di·at·ed, ir·ra·di·at·ing, ir·ra·di·ates
To expose to radiation, as for diagnostic or therapeutic purposes.
To treat with radiation.
To apply radiation to a structure or organism.