Units of Radiation

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Exposure [measured in Roentgen (R)]

Exposure is defined as the amount of charge liberated in air by x-ray or gamma photons.

1 Roentgen = 1.6 Trillion ion pairs per gram of air = 2.58E-4 Coulombs/kg

Absorbed Dose [measured in rad]

The absorbed dose is defined as the amount of energy deposited in matter (such as tissue) by radiation.

0.01 rad = 1 Joule per kilogram.

For x-rays, an exposure of 1 Roentgen gives an absorbed dose of  approximately 1 Rad.

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