Shielding Design
To first approximation shielding reduces the intensity of radiation exponentially depending on the thickness.
This means when added thicknesses are used, the shielding multiplies. For example, a practical shield in a fallout shelter is ten halving-thicknesses of packed dirt, which is 90 cm (3 ft) of dirt. This reduces gamma rays to 1/1,024 of their original intensity (1/2 multiplied by itself ten times). Halving thicknesses of some materials, that reduce gamma ray intensity by 50% (1/2) include:
| Material | Halving Thickness, inches | Halving Thickness, cm | Density, g/cm³ | Halving Mass, g/cm² |
|---|---|---|---|---|
| lead | 0.4 | 1.0 | 11.3 | 12 |
| steel | 0.99 | 2.5 | 7.86 | 20 |
| concrete | 2.4 | 6.1 | 3.33 | 20 |
| packed soil | 3.6 | 9.1 | 1.99 | 18 |
| water | 7.2 | 18 | 1.00 | 18 |
| lumber or other wood | 11 | 29 | 0.56 | 16 |
| air | 6000 | 15000 | 0.0012 | 18 |
Column Halving Mass in the chart above indicates mass of material, required to cut radiation by 50%, in grams per square centimetre of protected area.
The effectiveness of a shielding material in general increases with its density except for neutron shielding.
Read more about this topic: Radiation Protection
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—Herbert Spencer (1820–1903)
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—Robert Frost (1874–1963)