One coulomb corresponds to the charge on
ion
pairs . The average energy required to produce 1 ion
pair in air is 33.5 eV. So the
energy needed to produce ion pairs is:
Since 1 eV = 
joules this gives the energy
absorbed per kilogram of air for an exposure of
as 33.5 joules.
Materials other than air receiving an exposure of
will absorb a different amount of energy per gram.
Soft tissue of the body for example will absorb 37.2 joules for an exposure
of , providing the gamma-ray
energy is in the range 200 keV to 3 MeV.
This 37.2 joules per kilogram is called the absorbed dose received by
tissue exposed to
.