If optimal radiographic exposure is recorded at 72 inches with an air kerma of 1 mGy, what will be the air kerma if the distance is shortened to 60 inches?

To determine the air kerma when the distance is shortened from 72 inches to 60 inches, the inverse square law can be applied. This law states that the intensity (or exposure) of radiation is inversely proportional to the square of the distance from the radiation source.

Initially, at 72 inches, the air kerma is recorded as 1 mGy. When the distance is decreased to 60 inches, the new air kerma can be calculated using the formula:

[

I_1 / I_2 = (D_2^2) / (D_1^2)

]

where (I_1) is the initial kerma (1 mGy at 72 inches), (D_1) is the original distance (72 inches), (D_2) is the new distance (60 inches), and (I_2) is the new air kerma we need to find.

Substituting in the known values, we have:

[

1 , \text{mGy} / I_2 = (60^2) / (72^2)

]

Calculating the squares:

[

60^2 = 3600

]

[