Which formula is associated with the direct square law?

The direct square law is a fundamental principle in radiography that illustrates the relationship between the distance from the radiation source and the amount of radiation exposure received. The correct formula associated with the direct square law states that the ratio of the radiation exposure (mAs) at two different distances is equal to the square of the distance ratios.

In this context, the formula expresses that if the distance from the radiation source doubles, the exposure must increase by a factor of four to maintain the same image quality. The use of the square of the distances is crucial because it reflects the way that radiation spreads out as it travels away from the source—essentially, with the increase in distance, the intensity decreases by the square of that distance.

So, when using the correct formula, mAs1/mAs2 = D1^2/D2^2, it effectively allows a radiographer to calculate how much mAs should be adjusted based on changes in distance from the source to ensure consistent imaging results. This understanding is vital for achieving appropriate exposure without causing over or underexposure in radiographic images.