Question

1). a).You have 5 cm of shielding material that has a linear attenuation coefficient of
0.045 cm-1. How many TVLs is this?

b).A treatment room is designed for a 6 MV Linac. Primary thickness was 36 inches. It was
decided to upgrade to 18 MV. What would be the new thickness? Consider TVL(6 MV) = 14
inches and TVL(18 MV) = 18 inches of concrete.

Answer 1

1 (a) TVL is the tenth value layer, which means that it is the thickness of the layer required to absorb 90% of incident radiation. From Beer Lambert's Law we can write,

For the tenth value layer I will be 0.1 I0, which gives,

This is 5 cm, which is then, 5 cm in terms of TVL is,

5 cm is 9.8% of Tenth value layer.

(b) The attenuation coefficient can be written as,

Substituting in Beer Lambert Law we get,

The new thickness should be such that the output radiation is same as the initial case, therefore we can write,

Substituting values we get,

Therefore the new thickness required is 46.286 inches.