Exposure [measured in Roentgen (R)]
Exposure is defined as the amount of charge liberated in air by x-ray or
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.