ASNT Industrial Radiography Radiation Safety Practice Test

With 0.19 in. of lead as 1 half-value layer, what is the percentage reduction in exposure from a 0.38 in. thick lead?

1. 25%

2. 50%

3. 75%

4. 100%

The correct answer is: 75%

To determine the percentage reduction in exposure from a material using half-value layers, it's important to understand how half-value thickness works in radiation attenuation. Each half-value layer (HVL) reduces the intensity of radiation by half. In this scenario, 0.19 inches of lead represents one half-value layer. Therefore, 0.38 inches of lead represents two half-value layers, since it is twice the thickness of one half-value layer. Now, applying the concept of half-value layers: 1. The first layer (0.19 inches of lead) reduces the exposure by half. 2. The second layer (an additional 0.19 inches of lead) will halve the exposure again from what was left after the first layer. Thus, starting with an initial exposure, after the first half-value layer, you are left with 50% of the original exposure. After the second half-value layer, you will have half of that, which is 25% of the original exposure. To find the percentage reduction, we can calculate: - Initial exposure = 100% - Final exposure after two HVLs = 25% - Reduction = Initial Exposure - Final Exposure = 100% - 25% = 75% Therefore, with