Three radiation-related units you need to know

Hello, everyone. My name is Daichi, an expert providing the information on the radiation issues in an easy-to-understand manner.

Today, I would like to respond to the following question:

– There are a variety of radiation-related units, but it is complicated to differentiate and I would like to know their difference.

Table of contents of this article

I have been involved with the radiation-relevant issues, like the policy on the decontamination activities and the management of the Interim Storage Facility, after the accident of the Fukushima Daiichi Nuclear Power Plant in 2011.

I received a doctorate in the field of radiation, while working in Fukushima.

Three radiation-related units you need to know

First of all, it is enough if you familiarized yourself with the following three units.

– Radioactivity: Becquerel (Bq)
– Absorbed dose: Gray (Gy)
– Exposed dose: Sievert (Sv)

And you can learn the other units when necessary.

Variety of radiation-related units

By the way, what kind of units exist, other than the aforementioned units?

Below are the examples of other radiation-related units.

– Irradiation dose: R (Röntgen)
– Radioactivity: Ci (Curie)
– Absorbed dose: rad （Rad）
– Exposure dose: rem (Rem)

At this moment, however, the following units are usually used.

– Radioactivity: Bq (Becquerel) instead of Ci (Curie)
– Absorbed dose: Gy (Gray) instead of rad (Rad)
– Exposed dose: Sv (Sievert) instead of rem (rem)

The radiation-related units at least you need to know

Details regarding these three units touched in the chapter ‘Three radiation-related units you need to know’ are explained in the following chapters.

Radioactivity: Becquerel (Bq)

Radioactivity, as explained in this article, is equivalent to the ability (level of ability) of a boxer to throw a punch in the case of boxing.

Becquerel is the unit to describe magnitude of radioactivity and specifically it is represented by the number of disintegration of atom cores per unit time (usually 1 second).

In other word, if an atom core is disintegrated in one second, the radioactivity is defined as 1 Bq.

To put is simply, disintegration of an atom core is a phenomena in which radioactive materials change into more stable materials, by emitting radiation.

By the way, the name of this unit derives from the French physicist, Antoine Henri Becquerel, who discovered radiation.

Those who would like to learn more about difference between ‘radioactive material’, ‘radioactivity’ and ‘radiation’ can see detail in this article.

Absorbed dose: Gray (Gy)

Absorbed dose is equivalent to the amount of energy received by the punched person in the case of boxing (no violence!).

Gray is the unit to describe the magnitude of absorbed dose and it is represented by energy, which people receive by exposure to radiation.

Specifically it is represented by absorbed energy (J: Joule) per unit mass (usually 1 gram).

By the way, the name of this unit derives from the British physicist, Louis Harold Gray.

Exposure dose: Sievert (Sv)

In the case of boxing, exposure dose is equivalent to the amount of damage caused to the punched person.

Sievert is the unit to describe the magnitude of exposed dose, in other words, impact on people who are exposed to radiation.

For example, effective dose, which represents the amount of impact on whole body caused by exposure to radiation, is calculated based on the absorbed dose, taking also account of kinds of radiation as well as coefficients given according to the kinds of organs exposed to radiation.

By the way, the name of this unit derives from the Swedish physicist, Rolf Maximilian Sievert.

And the unit Sievert, which represents magnitude of exposed dose, has different kinds of meanings, although they are quite similar: e.g.

– Effective dose
– Committed effective dose
– Dose equivalent
– Ambient dose equivalent
– Personal dose equivalent

Difference between these units is elaborated in this article.

Summary

The radiation-related units which you need to know first are:

– Radioactivity: Becquerel (Bq)
– Absorbed dose: Gray (Gy)
– Exposed dose: Sievert (Sv)

and you can learn other units later when necessary.

By the way, the following videos are created, which explain the almost same contents above.

Please take a look at them at your convenience.

– Japanese version

– English version

Now this is the end of this article.

By the way, you can read the same article in Japanese here.

Thank you very much for reading this article.

See you next time!