If distance from source is doubled, exposure becomes what factor?

If distance from source is doubled, exposure becomes what factor?

• A. Twice as high
• B. Same
• C. Half as much
• D. One quarter

Answer: (D)

The key idea is the inverse square law: the dose rate from a point source is proportional to 1 divided by the distance squared. If you double the distance, the exposure becomes (1/(2)^2) = 1/4 of what it was. In other words, exposure is reduced to one quarter because the radiation spreads over a sphere whose surface area increases with the square of the distance. This is why increasing distance is such an effective protection method. For typical gauge sources, this relation is a good approximation, though very close or extended sources can have more complex behavior.

The key idea is the inverse square law: the dose rate from a point source is proportional to 1 divided by the distance squared. If you double the distance, the exposure becomes (1/(2)^2) = 1/4 of what it was. In other words, exposure is reduced to one quarter because the radiation spreads over a sphere whose surface area increases with the square of the distance. This is why increasing distance is such an effective protection method. For typical gauge sources, this relation is a good approximation, though very close or extended sources can have more complex behavior.