Dr. Tsubokura's Radiation Lecture Vol.151

Author: Masaharu Tsubokura M.D., PhD.

Editors: Yudai Kaneda, Akihiko Ozaki M.D.,PhD.,

301　 The unit "Sv" measures effects on the human body

October 24, 2021

If we compare radiation to sparklers, the tinder is the radioactive material, and the sparks are the radiation. The capability of emitting those sparks is radioactivity. If we compare radiation to a flashlight, the flashlight is the radioactive material, the light produced from it is the radiation, and the ability to produce light is the radioactivity.

　The units we use in radioprotection are the becquerel (Bq) and the sievert (Sv). The becquerel measures the capability of emitting radiation—simply the amount of radioactive material—and the sievert is a unit used to measure the effects on the human body. Therefore, the subject is always "things" when using the becquerel, while the subject of the sievert is "people" because it is a measurement for humans. It is expressed as in the following: this food has 〇〇 becquerels, this soil has 〇〇 becquerels, and so forth. In contrast, sieverts are expressed like this: eating this food has an effect of 〇〇 sieverts, or being in a certain place has an effect of 〇〇 sieverts.

　A sievert is the unit we use to measure the effect of radiation on humans as a "quantity." Although there are various kinds of radioactive substances, both artificial and natural, and several exposure routes, such as internal exposure and external exposure, this unit is designed to express the effects of radiation on the body by using a single number.

302　The sievert unit is used to quantify the effect

October 31, 2020

If we compare radiation to sparklers, the tinder is the radioactive substance, and the sparks are the radiation. The capability of emitting those sparks is radioactivity. The becquerel is a unit measuring the capability of emitting radiation—simply the amount of radioactive material—and the sievert is a unit used to measure the effect on the human body.

　The sievert is designed to express the effects of radiation on the body in a common way using a single number.

　It is not the radioactive substances themselves that affect people, but the radiation emitted by those substances. There are both artificial and natural radioactive substances, and the radiation they emit—alpha, beta and gamma rays—affects humans.

　The annual amount of radiation we receive from radioactive potassium—a naturally radioactive substance found mainly in food—is 0.18 millisieverts. However, in a study conducted in 2018, the annual amount of radiation we receive from radioactive cesium, which can also be found in food, is around 0.001 millisieverts.

　In this way, by using the unit of a sievert, we can express the effect of radiation on humans as a "quantity," regardless of whether it is an artificial or natural radioactive substance.