Emory University
Radiation Safety Office
Laboratory Worker Training Manual

 TYPES OF RADIATION
 Three basic types of radiation may be found in the laboratories at Emory:
Alpha particles
  Beta particles
Gamma or X-rays

           Alpha particles are very large and therefore have little penetrating power.  They can be easily shielded by a sheet of paper or by the outer layer of skin.  The exposure hazard, consequently, is not external but rather internal.  If ingested or inhaled they will produce a great amount of damage in a small area.  The only experience with alpha sources at Emory will be with sealed sources.
         Beta particles are ordinary electrons and can be positively or negatively charged.  They are emitted from the nucleus of an atom in which the neutron to proton ratio is too high.  ³²P decays by beta emission to ³²S:

        The most common beta emitters on campus at Emory are ³H, ¹⁴C, ³⁵S and ³²P.  The penetrating power of the beta particle depends on its energy.  The betas emitted by ³H, ¹⁴C, and ³⁵S are all low energy betas and are therefore not an external hazards.  In fact, the low energy betas will not cause the film on the dosimeter to be exposed.  Also, the ³H beta cannot be detected with the survey meter, and a very sensitive probe is necessary to detect the ¹⁴C and ³⁵S.  However, these materials are capable of causing internal damage like alpha particles.  Protective clothing should be worn when handling these materials, but no additional shielding is necessary.  If there is a possibility of volatility, the materials should be used in the fume hood.
        The high energy betas such as those emitted by ³²P and ⁹⁰Y are more penetrating and therefore present an external exposure hazard, especially to the skin.  Shielding is necessary when working with these high energy betas.  A low Z, i.e. less dense,  material such as plexiglass or Lucite is preferred for the following reason.  When a beta is incident upon a high Z material such as lead, the beta particle interacts with the orbital electrons and slows down emitting characteristic x-rays known as bremsstrahlung. 
 
 
 
 
 
 
 
 
 
 
 

The less dense material does not have the abundance of orbital electrons and therefore the bremsstrahlung is not as prominent.  Many commercial shields are available for bench work, test tubes and solid and liquid waste containers.  Double gloving for procedures will also provide additional protection to the hands when working with concentrated stock solutions.
         Gamma radiation is a high energy form of electromagnetic radiation similar to visible light, ultraviolet rays and radio waves.  Gamma rays have no mass and no charge and are, therefore, penetrating and can travel long distances in air and other materials.  Common gamma emitters on campus at Emory include ¹²⁵I (0.035 MeV), ⁵¹Cr (0.320 MeV), ¹³⁷Cs (0.662 MeV) and ⁶⁰Co (1.17 and 1.33 MeV).  The proper shielding for gamma or x-rays is lead.  A thicker sheet of lead would adequately stop all gamma or x-rays.