Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Gray (Gy) is a unit of absorbed radiation dose in the International System of Units (SI). It measures the amount of radiation energy absorbed per kilogram of matter, where 1 Gy equals 1 joule per kilogram.
5 Must Know Facts For Your Next Test
The gray (Gy) is named after British physicist Louis Harold Gray, a pioneer in the field of radiation dosimetry.
One gray is equivalent to 100 rads, an older unit of absorbed dose.
Gray is used to quantify the absorbed dose for both ionizing radiation and non-ionizing radiation.
In medical contexts, gray is important for understanding the dosage delivered during radiotherapy treatments.
Biological effects of radiation are often measured in grays to assess potential damage to tissues and organs.
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Related terms
Sievert (Sv): A unit that quantifies the risk associated with exposure to ionizing radiation. It accounts for both the energy absorbed and the biological effects on human tissue.
Rad: An older unit of absorbed radiation dose. One rad is equal to $0.01$ gray ($1 \text{ Gy} = 100 \text{ rads}$).
Becquerel (Bq): A unit that measures radioactivity representing one disintegration per second.