ASNT Industrial Radiography Radiation Safety Practice Test

If shielding reduces the exposure rate to one-half, how many half-value layers would be required to significantly decrease exposure?

1. One half-value layer

2. Two half-value layers

3. Three half-value layers

4. No half-value layers

The correct answer is: One half-value layer

To understand why the first choice is highlighted as correct, it's important to grasp the principle of the half-value layer (HVL) in radiation shielding. The half-value layer is defined as the thickness of material needed to reduce the intensity of radiation to half its original value. If shielding can decrease the exposure rate by a factor of one-half, then only one half-value layer is required to achieve that specific reduction. In practical terms, using a single half-value layer significantly reduces exposure to a manageable level. Therefore, if the question emphasizes "reducing exposure" to "one-half," it directly correlates with the definition of a single half-value layer. To further decrease exposure beyond this, additional layers would be required, but the question does not hint at a desire for additional reductions; it simply specifies the first significant decrease. As the question relates to the effectiveness of shielding, understanding that one half-value layer effectively cuts the exposure rate in half aligns with common practices in radiation safety. Therefore, the conclusion that only one half-value layer is necessary for this significant reduction is consistent with the established radiation protection principles.