ASNT Industrial Radiography Radiation Safety Practice Test

What exposure reduction does a piece of lead 0.38 in. thick provide?

1. 50%

2. 75%

3. 100%

4. 25%

The correct answer is: 75%

The thickness of lead in this context is used as a shielding material to reduce exposure to radiation. A lead thickness of 0.38 inches can significantly attenuate radiation exposure, especially for gamma rays and X-rays. To understand the level of exposure reduction provided by lead of this thickness, it's essential to look at the concept of half-value layer (HVL). The HVL is the thickness of material needed to reduce the radiation intensity by half. For lead, the HVL for many types of high-energy radiation is typically around 0.2 inches to 0.4 inches, depending on the energy of the radiation. If we consider that 0.38 inches is approximately one HVL for certain radiation types, it means that passing through this amount of lead could reduce the radiation exposure to about 50% of its original intensity. Since 0.38 inches of lead could be close to one HVL for common industrial radiography sources, it allows for the assumption that the exposure reduction could be substantial, often around 75%. This fits within common shielding practices, where just over one HVL can achieve an effective dose reduction of around this magnitude. Thus, the correct choice reflects this understanding of radiation attenuation through lead shielding, highlighting how a