Dr. Tsubokura's Radiation Lecture Vol.5

Author: Masaharu Tsubokura

Editors: Mariko Irie, Izumi Yoshida, Yuki Senoo

9. The distinction between becquerel (Bq) and sievert (Sv)

Becquerel is the unit of radiation (simply the amount of radioactive substances), and sievert is the magnitude of the impact on the human body.

Therefore, when using the becquerel, “thing” is the subject, and when using the sievert, the subject is “human beings.” This food is XX becquerel, and this soil is XX becquerel, while the effect on your body due to eating the food is XX sievert, and the impact on humans in a spatial dose location is XX sievert.

There is about 3000 becquerel of radioactive potassium in the human body. This indicates the human body is regarded as a "thing," and we consider the radioactive substances contained in it.

The resulting impact on the person himself or herself will be about 0.2 millisieverts per year.

10. "1 micro" equals " one-thousandth of a "milli”

When we talk about radiation exposure, units such as “milli” sieverts or "micro" sieverts come up.

One "millimeter" is one-thousandth of a meter (written with three "0s"), and one "micro" meter is one-millionth of a meter (six "0s"). These units change every three increments of "0" (every 1,000 times).Conversely, 1,000 times one meter is a “kilometer” (1,000 meters is 1 kilometer), and 1,000,000 times is “mega” (1 megabyte on a PC is 1,000,000 bytes).

We use as the spacial dose 0.2 or 0.3 "micro" sieverts per hour, and the influence on the body is 100 "milli" of sieverts or 1 "milli” sievert.

One "milli" has three more "0s" than 1 "micro" (1 "milli” = 1,000 “micro”).By the way, after “mega,” it will continue with “Giga” and “Tera” on a personal computer. Before "micro" is "nano” and “pico.”


The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on March 8th and 15th 2015,and was reproduced for MRIC Global under the author's permission.

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