RAD (RADiation Unit)

A rad is a legacy unit of absorbed radiation dose (by human tissue, air, water, or any other substance), mostly only still being used in the United States (US). It has been replaced by the SI (International System of Units) unit of gray (Gy), specified by the US National Institute of Standards and Technology (NIST). Absorbed radiation dose may be one or more of neutron, gamma, natural-light, ultraviolet or x-ray radiation. Look up 'electromagnetic radiation'

1 rad = 0.01 Gy.

Exposure Levels

• < 100 rad (1 Gy) - blood changes
• 100 - 200 rad (1-2 Gy) in < 24hrs may cause acute radiation syndrome (ARS)
• 200 - 1000 rad (2-10 Gy) in a matter of hours (or less) will result in serious illness and is potentially fatal

• 1000 rad (10+ Gy) are typically fatal

Distance from source, length and time of exposure, as well as how much of the body is exposed all contribute to how much radiation is absorbed.

References

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Created: 2026-05-12

Last Updated: 2026-05-15