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Radiation Shielding Calculation

SHIELDING CALCULATIONS

The simplest method for determining the effectiveness of the shielding material is using the concepts of half-value layers (HVL) and tenth-value layers (TVL).
One half-value layer is defined as the amount of shielding material required to reduce the radiation intensity to one-half of the unshielded value.

The symbol  is known as the linear attenuation coefficient and is obtained from standard tables for various shielding materials.

One tenth-value layer is defined as the amount of shielding material required to reduce the radiation intensity to one-tenth of the unshielded value.

Both of these concepts are dependent on the energy of the photon radiation and a chart can be constructed to show the HVL and TVL values for photon energies.

Photon
Energy
(keV)

HVL (cm)

Lead
(11.35 g/cm3)

Iron
(7.86 g/cm3)

Concrete
(2.4 g/cm3)

Water
(1.0 g/cm3)

500

0.38

1.0

3.3

7.2

1000

0.86

1.5

4.5

9.8

1500

1.2

1.8

5.6

12.0

2000

1.3

2.1

6.4

14.0

3000

1.5

2.4

7.9

17.5

The basic calculational approach to photon shielding is to determine the existing exposure rate, decide on the desired exposure rate after shielding and then calculate how many HVL or TVL will be needed. The basic equation for using the HVL concept is:

The basic equation for using the TVL concept is:

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