ASNT Industrial Radiography Radiation Safety Practice Test

The use of how many half-value layers will reduce the exposure by a factor of 16 times?

1. 2 half-value layers

2. 3 half-value layers

3. 4 half-value layers

4. 5 half-value layers

The correct answer is: 4 half-value layers

The correct choice is based on the understanding of how half-value layers function in the context of radiation exposure. A half-value layer (HVL) is defined as the thickness of material required to reduce the intensity of radiation to half its original value. When you transmit radiation through one half-value layer, the exposure is reduced to 50% of its initial value. If we consider multiple half-value layers, the exponential decay can be calculated as follows: - After 1 half-value layer, the exposure is \(1/2\) of the original. - After 2 half-value layers, the exposure is \(1/2 \times 1/2 = 1/4\) of the original. - After 3 half-value layers, the exposure is \(1/2 \times 1/2 \times 1/2 = 1/8\) of the original. - After 4 half-value layers, the exposure is \(1/2 \times 1/2 \times 1/2 \times 1/2 = 1/16\) of the original. Thus, it takes 4 half-value layers to reduce the exposure by a factor of 16. This understanding is essential in