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RADIATION AND
RADIOACTIVITY
Gamma Rays and X-Rays
Gamma radiation is a high energy
ionizing radiation called gamma
photons that are emitted from the
nucleus of radioactive ions. Because of
their high energy gamma rays travel at
the speed of light and can travel a long
distance before expending their
energy. They also have the ability to
penetrate objects and human tissue. A
dense material such as lead is required
for proper shielding of gamma emitters.
The major difference between gamma
rays and X-rays is how they are
produced. Gamma rays originate in the
nucleus while X-rays originate in the
electron field surrounding the nucleus
and are machine produced.
Common Gamma Emitters
Energy (MeV)
Cesium-137*
0.662
Iodine-125
0.035
Iodine-131*
0.364
Technecium-99m 0.140
*Also decays by beta emissions. Refer to Beta
Emitters section.
