Being exposed to ionizing radiation or to radioactive material.
(http://www.nukeworker.com/forum/index.php?action=dlattach;topic=6669.0;attach=909;image;nothumb)
A term relating to the amount of ionizing radiation that strikes a living or inanimate material. (This is a general definition. In health physics, exposure is specifically defined as a measure of ionization in air caused by x-ray or gamma radiation only.)
http://www.epa.gov/radiation/understand/pathways.htm