D–4
Types of Radiation
The radioactive sources in the gauge produce four types of
radiation:
Alpha particles
Beta particles
Gamma rays (photons)
Neutrons
The alpha and beta particles are stopped by the source capsule.
Therefore, they present no external hazard to personnel. Only
the gamma and neutron radiation from sealed sources
contribute to any occupational radiation exposure.
Gamma rays (photons) are a type of electromagnetic radiation,
like X rays, radio waves, and visible light. Photons have no mass
or electrical charge, and travel at the speed of light. Gamma rays
are energetic and penetrating. Dense materials (such as lead,
tungsten, and so on) provide the best shielding against gamma
radiation.
Neutrons are a form of particulate radiation but, unlike alpha
and beta particles, they have no electrical charge. This makes
neutron radiation very penetrating. Fast neutrons lose energy
primarily by so-called “billiard ball” elastic collisions with the
nuclei of low atomic number atoms, especially hydrogen. The
best shielding materials for fast neutrons are those with a high
hydrogen content, such as water, concrete, and polyethylene.
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