Metals(SHIELDING MATERIALS)

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There are two types of radiation shielding, thermal and biological. Thermal shielding is used to dissipate excessive heat from high absorption of radiation energy, and biological shielding is used to protect people from harmful effects of exposure to ionizing radiation. The type of shielding material to use depends on the stopping power of radiation particles and the type and energy of radiation. Example of shielding material is Lead.

Lead materials are highly used in shielding ionizing radiation because of their high molecular density. The high density is because of combination of its atomic mass and relatively small size of its bond lengths and atomic radius. Pure lead is brittle and cannot be worn as an apparel. Therefore it is mixed with binders and additives to make flexible lead vinyl sheet and wearable radiation shielding materials. Lead can also be mixed with other lighter weight metals such as tin, rubber and PVC vinyl to form lead composite shielding. The lead composite varies with the manufacturer’s proprietary blends.

Example of Shielding Materials that contain Lead:

  • Lead sheet and slab. They are used for permanent shield installation.
  • Lead bricks. Lead bricks are movable, easy to handle and can be re-used. They are more resistant to damage than concrete.
  • Lead aprons and gloves. They are protective clothing that reduce radiation exposure to various body organs during medical imaging that uses X-rays.
  • Lead glass. They are used for transparent shielding. Example in the X-ray or CT room they provide view to the patient during treatment.
  • Lead laminated panels. They offer self-supporting nature and greater ease in erecting and handling.
  • Lead shielded doors and door frames.

Non-lead and lead-free shielding materials offer the same protection as lead-based composite shielding. They are made up of a mixture of additives, binders and attenuating heavy metals that block or absorb radiation as lead. Example of metal used are: tin, tungsten, antimony and bismuth. Advantage of lead-free materials is that, they are environment friendly and can be recycled conveniently.

Factors to consider when choosing shielding material

  • Type of procedure to be performed
  • Frequency of the procedure
  • Length of the procedure
  • Attenuation of the radiation used
  • Energy of the radiation source
  • Maximum allowable dose rate
  • Machine utilization factors and amount of leakage radiation
  • Distance from source to point where protection is needed.
  • Size and location  of openings in the barrier

Application of shielding materials

  • Protection against X-rays. Exposure to X-rays can cause damage to living cells hence it is necessary to shield the x-ray units with a material that can block or absorb the rays.
  • Gamma ray shielding. A dense shield material with a higher atomic number is used to stop gamma rays since attenuation is dependent upon the density of the shielding material.
  • Protection against neutrons in nuclear reactors. In neutron shielding, a material that cannot become radioactive is required. This is because there is production of secondary radiation within a shield material by neutron absorption. Attenuation of neutrons is dependent upon the effective cross section of the shield.

REFERENCES

  1. A Guide to the use of Lead for Radiation Shielding. Retrieved from: www.canadametal.com/radiation-protection on 2018/12/5.
  2. Wikipedia. 2018. Radiation Shielding.

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