What happens to radiation intensity if the distance between the source and the object increases?

• A. decreases
• B. increases
• C. remains the same
• D. varies depending on kilovolt peak and milliampere-seconds

Answer: (A)

Radiation intensity at a point follows the inverse square law: as distance from the source increases, the beam spreads over a larger surface area, so fewer photons reach any given area. This means the intensity decreases proportional to 1/d^2. For example, doubling the distance cuts intensity to one quarter, and tripling it reduces intensity to one ninth. So, when distance increases and other factors are held constant, the intensity at the object decreases. Kilovoltage peak and mAs affect beam quality and total photon quantity, but the specific change due to distance is governed by the inverse square relationship, not by those factors.