What is the difference of Gy and Sv?


Question:

Why is “Sv” always used as a unit of radiation energy instead of “Gy”? And could you tell me the relations between “Sv”, “Gy” and “Bq”? (Male, 30s, Tokyo)

Answer:

It might be confusing to see or hear about many different units about radiation in the news these days. But once you understand the meanings of each unit, it will be much easier to figure out what they are talking about in reference to radiation and radioactive materials.

Becquerel (Bq): This is an International Standard unit that measures the radiation decay (transformation) of radioactive material
Gray (Gy): This is also an International Standard unit that measures the physical absorption of radiation by 1 kg of matter
Sievert (Sv): This, too, is an International Standard unit that evaluates and measures the biological effects of radiation (usually on the human body)

Let's compare the three measuring units using the idea of a baseball pitcher. The pitcher would be compared to radioactive material, and the balls thrown would be compared to radiation.

Becquerel (Bq): Number of balls a pitcher can throw in 1 inning --> 1 minuite
Gray (Gy): When the ball hits an object, for example a bat or the batter, then Gy is the energy that the ball gives that object.
Sievert (Sv): Now, let's say the pitcher is not very good and the ball hits the batter. The Sv is the damage on the batter by the ball, such as a broken bone of the batter's arm where the ball hit.

Even if the emitted energy of radiation is the same, the damage (sievert) a human (batter) receives can be different by the types of radiation. Using the pitcher ? ball ? batter example again, imagine when balls hit a batter. Even if the speeds of balls are the same, the damages would be different by the TYPES of the balls. If it is a very hard ball, the damage would do more serious, or a soft sponge ball would give hardly any damage. A strange ball with hard sharp points all over would give a lot of damage on the batter.

Plus, even if the emitted energy of radiation is the same, the damage done to a human's organs would differ by the TYPES of organs in our human body. There are organs that are more susceptible to damage by radiation and there are organs that are less susceptible. For example, the gonads are 20 times more susceptible to damage by radiation than the human skin and the surface of bones. These differences may be similar to the differences of damage when a ball hits the batter's hips or an eye.


Science Communicator: Moeko Tabata