ASNT Industrial Radiography Radiation Safety Practice Test

If 0.19 in. of lead provides 1 half-value layer, how much exposure is reduced from 0.57 in. of lead?

1. 12.5% reduction

2. 25% reduction

3. 50% reduction

4. 75% reduction

The correct answer is: 75% reduction

In radiation safety, the concept of a half-value layer (HVL) is crucial for understanding how different materials attenuate radiation exposure. A half-value layer is defined as the thickness of a specified material needed to reduce the intensity of radiation to half its original value. If 0.19 inches of lead provides one half-value layer, this means that using this thickness results in a 50% reduction in exposure. Now, when considering 0.57 inches of lead, we can first determine how many half-value layers this thickness corresponds to. By dividing the available thickness (0.57 inches) by the thickness of one half-value layer (0.19 inches), we find that 0.57 inches of lead represents approximately 3 half-value layers (0.57 / 0.19 ≈ 3). Each half-value layer reduces radiation exposure by 50%. The cumulative effect of multiple half-value layers can be calculated as follows: the exposure is halved with each additional HVL. Therefore, after the first half-value layer, the remaining exposure is 50% of the original. After the second half-value layer, it’s reduced to 25% of the original (50% of the remainder from the first layer),