How is gray different from sievert?

How is gray different from sievert?

The gray is a unit used to measure physical quantity (e.g., “how much energy is deposited in the human body by radiation”). It is known, however, that biological effects of radiation on living beings vary depending on the types of radiation even if the same amount of energy (dose) is deposited. Sievert is used to complement this.

Sievert can be determined by the following formula:

Sievert = Biological effectiveness factor unique to the type of radiation * Gray

Therefore, sievert is used to discuss the effects of radiation exposure, and the current Laws Concerning Prevention from Radiation Hazards due to Radioisotopes and others are based on this unit. For this reason, while the gray is known as a unit of physical quantity, the sievert is known as a unit of radiation protection-related quantity. The factor is one for gamma ray and beta ray, and ranges from five to 20 for neutron, alpha ray, and heavy particle. Therefore, one may assume Gy = Sv since ordinary radiation exposures are x- and gamma-ray exposures except for special cases, such as the JCO accident.

Radiation Units

(Source: Ministry of Education, Culture, Sports, Science,and Technology)

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