What is the relationship between sievert and becquerel?

Answer 1

These units measure different things.

Becquerel is a measure of radioactivity in a radioactive material, it tells how many events occur in given material in a second.

Sievert is a measure of absorbed ionizing radiation with compensation regarding biological effect.

123456 Becquerel happens inside the radioactive material, and it says 123456 events occur per second in the measured item.

0.129 Sievert happens inside a biological entity (you) and says the radiation absorbed by your body will have a biological effect that is eqivalent to absorbing 0.129 joule of beta radiation per kilogram of body.

Also it might be worth noting that becquerel is a very small unit, Sievert is a huge one.

For example, natural potassium (40K) in a typical human body produces 4,000 disintegrations per second, 4 kBq of activity.

The Fukushima workers radiation dose limitation was raised to 1/4 Sievert. At that much radiation the company can hope that no one will die of radiation poisoning.

Any workers receiving that dose will likely suffer from an increased risk of cancer. How much of an increase is difficult to say.