If an optimal radiograph is acquired at 72 inches with an air kerma of 4 milligray, what will the air kerma be if the distance is reduced to 40 inches?

When considering how air kerma changes with distance, the inverse square law is a critical concept. The law states that the intensity of radiation at a certain distance from a source is inversely proportional to the square of the distance from that source. This means that as the distance decreases, the intensity or air kerma increases significantly.

In this scenario, the original air kerma is 4 milligray at 72 inches. To find the air kerma at 40 inches, you can use the inverse square law formula:

Air Kerma at new distance = Original Air Kerma × (Original Distance / New Distance)²

First, you plug in the values:

• Original Air Kerma = 4 mGy

• Original Distance = 72 inches

• New Distance = 40 inches

Now calculate using the formula:

Air Kerma at 40 inches = 4 mGy × (72 inches / 40 inches)²

Calculating the ratio:

(72 / 40) = 1.8, and then squaring it gives you 3.24.

Next, multiply:

Air Kerma at 40 inches = 4 mGy × 3.24 = 12.96 mGy, which can