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• Neutrons.

Figure 8.1 – Non ionizing and ionization radiation

Alpha radiation colliding with atoms gives up its energy in a very short
distance, such as the thickness of a sheet of paper, less than the thickness of skin,
or a few centimeters of air. Consequently, alpha particles emitted by radioactive
materials are not likely to be harmful when striking the outside of a human body
that is protected by clothing and the outermost dead layer of the skin. However,
when these same alpha-emitting radionuclides are taken into the body, their
emissions can directly irradiate nearby cells of tissues in which they are deposited
and may cause cellular changes. Such changes may result in adverse health effects
in the short or long term, depending on the nature of the changes. Alpha-emitting
radionuclides may be encountered in contamination created by intentional or
accidental dispersion of nuclear weapon-source materials (e.g., plutonium-239) or
as a result of a nuclear detonation. Alpha-emitting radionuclides, such as radium in
soil and radon in air, are also naturally occurring sources of radiation and
contribute to normal background levels.
In comparison to alpha radiation, fast-moving electrons, which are known as
beta particles, have much smaller mass and electric charge, are more deeply
penetrating, and dissipate their energy over a larger volume of tissue. Even high-
energy beta particles, however, will transfer most of their energy and come to a
stop within about 1 centimeter of plastic, 1 to 2 centimeters of tissue, or 4 to 5
meters of air. Therefore, beta particles that strike the outside of the body will
penetrate only a short distance, but they may travel far enough to damage the
actively dividing cells of the skin. Beta-emitting radionuclides are of most concern
after they have entered the body and can transfer their energy to nearby cells of
internal organs. Beta-emitting radionuclides may be found in contamination
consisting of fission products from a nuclear detonation or resulting from the

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