Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Rad stands for radiation absorbed dose, which measures the amount of ionizing radiation energy absorbed by a material. It is equivalent to 0.01 joules of energy deposited per kilogram of tissue.
5 Must Know Facts For Your Next Test
One rad equals 0.01 gray (Gy) in the International System of Units (SI).
Rad is commonly used in the United States, whereas gray is more commonly used internationally.
The biological effects of ionizing radiation are often measured using rads to determine potential damage to tissues.
Different types of radiation (e.g., alpha, beta, gamma) have different biological impacts even if the same number of rads are absorbed.
The rad has largely been replaced by the gray in medical and scientific literature but remains an important historical unit.
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Related terms
Gray (Gy): A unit in the International System of Units (SI) used to measure absorbed radiation dose, where one gray equals one joule per kilogram.
Sievert (Sv): A unit that accounts for biological effects of radiation, where one sievert represents a higher risk factor compared to one gray due to varying sensitivity across tissues.