ASNT Industrial Radiography Radiation Safety Practice Test

What factor does doubling the distance from the radiation source have on exposure?

1. The exposure increases by a factor of 2

2. The exposure remains the same

3. The exposure decreases by a factor of approximately 4

4. The exposure increases by a factor of 4

The correct answer is: The exposure decreases by a factor of approximately 4

Doubling the distance from a radiation source significantly affects the exposure due to the inverse square law of radiation. This principle states that the intensity of radiation is inversely proportional to the square of the distance from the source. When you double the distance, the intensity of radiation (and therefore the exposure) decreases by a factor of the square of that distance change. Mathematically, this can be represented as: - If the original distance is \( d \), and the new distance is \( 2d \), then the exposure at the new distance can be calculated as: \[ \text{New Exposure} = \frac{\text{Original Exposure}}{(2)^2} = \frac{\text{Original Exposure}}{4} \] Thus, at a distance that is double the original distance, the exposure decreases to one-fourth of its original value, which is why this option is correct. Understanding this relationship is crucial for minimizing radiation exposure in industrial radiography settings and forms the basis for safe operational practices.