What unit is used to express the dose of radiation in food irradiation?

• A. Gy
• B. kGy
• C. J
• D. Sv

Answer: (B)

In food irradiation, you’re concerned with how much energy is deposited per kilogram of food, i.e., the absorbed dose. The unit for absorbed dose is the gray (Gy), which is defined as 1 joule per kilogram. Since the doses used to achieve microbial inactivation are quite large, we express them in kilograys (kGy), where 1 kGy equals 1,000 Gy. So a dose of 5 kGy means 5,000 J deposited per kilogram of food.

Joules measure energy, not dose per mass, so they aren’t the standard way to report irradiation dose. Sieverts represent dose equivalent used for health risk assessment in people, not the actual energy absorbed by the food. Gy is the basic unit, but for practical food irradiation dosing we use kGy because the values are in the thousands of grays.