Federal Emergency Management Agency (FEMA) Standardized Awareness Practice Test

When doubling the distance from a radiation source, how is exposure affected?

1. It remains the same

2. It doubles

3. It reduces to one-fourth

4. It increases by one-half

The correct answer is: It reduces to one-fourth

When the distance from a radiation source is doubled, exposure to radiation reduces to one-fourth of the original exposure level. This outcome is a result of the inverse square law, which states that the intensity of radiation or any similar phenomenon is inversely proportional to the square of the distance from the source. In practical terms, if you double your distance from the source, the increase in distance causes the radiation to spread over a larger area, which decreases the intensity you experience. Specifically, if the distance is increased, the exposure decreases dramatically: for instance, if the initial exposure was measured at one unit, moving to a distance that is twice as far leads to an exposure of one-fourth of that unit, illustrating how distance significantly impacts safety in situations involving radiation. Therefore, this principle underscores the importance of maintaining safe distances from radiation sources to minimize exposure effectively.