What exactly does it mean to irradiate food?

Scientists have experimented with irradiation as a preservation method since the early part of this century. It exposes the food to ionizing energy, usually from a radioactive source such as cobalt 60. In low doses, radiation kills microorganisms and insects. In higher doses, it sterilizes food and destroys more microorganisms. The radiation energy passes through the food, and most is not absorbed. Absorption depends on the chemical makeup of the food.