L. Decontamination and Shielding Requirements

6. Shielding Radioactive Material

It is often necessary to shield radioactive material to reduce the exposure rate and achieve ALARA (i.e., the philosophy of maintaining exposures "as low as reasonably achievable"). Shielding should be added to any material with an exposure rate greater than 2 mR/hr (or equivalent count rate) at 30 cm. Although it is advisable to consult with the RSO regarding shielding needs and/or design, the following are some practical methods:

  1. Alpha particles and low energy beta particles (i.e., < 300 keV):

    2. By their nature, alpha and low energy beta particles do not pose a significant external radiation hazard; therefore, any container provides adequate shielding. Contamination control to prevent ingestion and inhalation is the primary concern.

  2. High energy beta particles:

    3. Additional shielding for high energy beta emitters (e.g., 32P) should be made of a low atomic number material (e.g., wood, Lucite, etc.). It is important to note that high atomic number shields (e.g., lead) for high energy beta emitters may result in the production of bremsstrahlung x-rays which are more penetrating than beta radiation. Ideally, high energy beta emitters should be shielded with a low atomic number material (for beta radiation) followed by a high atomic number material (for bremsstrahlung x-rays produced by the beta shield).

  3. X-rays and Gamma Rays:

These types of radiation are generally shielded with lead or other dense material such as concrete. It should be noted that lead (Pb) is a hazardous material and contact with the skin may result in absorption of the lead. Application of some type of coating (e.g., duct tape) will minimize this potential hazard. The necessary thickness of shielding is variable and dependent upon several factors. In most cases, the container provided by the radionuclide vendor provides adequate shielding.

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