American Registry of Radiologic Technologists (ARRT) Practice Exam

When the distance from the x-ray source is halved, the beam intensity increases four times. This phenomenon is explained by the inverse square law, which states that the intensity of radiation from a point source is inversely proportional to the square of the distance from the source.

According to the inverse square law, if you halve the distance (for instance, moving from 100 cm to 50 cm), the intensity of the radiation increases by a factor equal to the square of the change in distance. Specifically, if the distance is reduced to half, the calculation would be as follows:

Intensity ∝ 1/distance².

So, if the distance is halved (1/2), the increase in intensity can be calculated as:

(1/(1/2)²) = 1/(1/4) = 4.

This means that the intensity increases by a factor of four when the distance is halved. Understanding the relationship defined by the inverse square law is fundamental in fields like radiologic technology, as it helps professionals gauge the necessary safety measures and equipment adjustments needed based on proximity to the x-ray source.