ASNT Industrial Radiography Radiation Safety Practice Test

With 3 half-value layers of lead, what would be the exposure rate from an initial rate of 100 mR?

1. 50 mR

2. 25 mR

3. 12.5 mR

4. 6.25 mR

The correct answer is: 12.5 mR

To determine the exposure rate after passing through three half-value layers (HVL) of lead from an initial rate of 100 mR, it's essential to understand the concept of half-value layers. Each half-value layer reduces the exposure rate by half. Starting with an initial exposure rate of 100 mR: 1. After passing through the first half-value layer, the exposure rate is halved, resulting in 50 mR. 2. The second half-value layer further halves this rate, reducing it to 25 mR. 3. Finally, the third half-value layer cuts the exposure rate in half once again, bringing it down to 12.5 mR. Thus, after three HVLs, the correct exposure rate is 12.5 mR, demonstrating the cumulative effect of attenuation through successive layers of material. This concept highlights the importance of understanding how radiation is influenced by various shielding materials, a critical aspect of radiation safety in industrial radiography.