If the half-value layer of shielding material is equal to 2 mm, how much radiation will transmit through 6 mm of this material?

• A. 12.5% of the original quantity
• B. 50% of the original quantity
• C. 25% of the original quantity
• D. 75% of the original quantity

Answer: (A)

The key idea is the half-value layer: each HVL thickness halves the radiation that passes through. With an HVL of 2 mm, every additional 2 mm halves what remains. After 2 mm: 50% remains; after 4 mm: 25% remains; after 6 mm: 12.5% remains. So 6 mm transmits 12.5% of the original radiation, since three HVLs have been traversed (1/2)³ = 1/8 = 12.5%.