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Radioactivity, radiation and radioactive materials

To print view 2023年2月10日更新

Three commonly confused words. In order to understand information correctly, it is necessary to grasp the meaning of each word.

To illustrate using a bonfire analogy

bonfire analogy

Types of radiation and penetrating power

The ability of radiation to penetrate through materials varies depending on its type. To block radiation effectively, it is necessary to use materials corresponding to its penetrating power.​Types of radiation and penetrating power

Units of radiation

Since the type and amount of energy of the radiation emitted varies according to the type of radioactive material, it is necessary to compare the degree of effect of radiation on the human body using the unit "Sievert" (Sv), which represents the level of effect on the human body, rather than the unit "Becquerel" (Bq).

Units of radiation

Regarding half-life

All substances are composed of atomic nuclei and the electrons that surround them. Radioactive materials, such as uranium, have an unstable balance between their atomic nuclei and electrons, causing them to emit radiation in order to reach a stable state. This transformation is known as "decay", and the level of radioactivity is halved after a certain period of time. The term "half-life" refers to the time it takes for the number of initial atomic nuclei to be reduced by half through decay. The half-life varies depending on the type of radioactive material, ranging from over 10 billion years to mere seconds. (*The image is for illustrative purposes only.)

Regarding half-life
(*The image is for illustrative purposes only.)

Radioactive materials(Radioactive Elements)  Radiation Emitted* Physical Half-Life
Thorium-232 Alpha, Beta, Gamma 14.1 billion years
Uranium-238 Alpha, Beta, Gamma 4.5 billion years
Potassium-40 Beta, Gamma 1.3 billion years
Carbon-14 Beta 5,700 years
Cesium-137 Beta, Gamma 30 years
Strontium-90 Beta 29 years
Cesium-134 Beta, Gamma 2 years
Iodine-131 Beta, Gamma 8 days
Radon-220 Alpha, Gamma 56 seconds

 *Includes radiation from decay products (resulting from the transformation of atomic nuclei emitting radiation)
Source: Japan Radioisotope Association, "Radioisotope Pocket Data Book 11th Edition"

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