In food irradiation, food is exposed to a carefully measured amount of ionizing radiation.
This is done in a special processing room or chamber for a specified duration of time.
With food irradiation, radiant energy (electrons, gamma rays, or x-rays) breaks chemical bonds, just as in cooking, but so few bonds are broken that the food is like fresh.
With a low level treatment, the sprouting of foods like onions and potatoes is stopped. With additional treatment insects which would eat fruit or grains are destroyed. A higher treatment acts as a "cold pasteurization" and destroys a significant amount of bacteria that could lead to foodborne disease.
Still higher treatment is used to make food "shelf stable," like canned food, but without the flavor changes characteristic of canned food. Astronauts have eaten shelf stable irradiated foods since the beginning of the space program.