If at one foot from the radiation source, the intensity of the exposure is 240mR/hour, what would be the total exposure after standing at a distance of 6" for 20 minutes?

To determine the total exposure after standing at a distance of 6 inches from the radiation source for 20 minutes, it is important to first understand how the intensity of radiation changes with distance, as well as how to calculate the accumulated exposure over time.

The exposure rate at one foot (12 inches) is given as 240 mR/hour. When moving closer to the radiation source, the intensity increases according to the inverse square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source.

In this case, you are moving from one foot (12 inches) to 6 inches. Since 6 inches is half of 12 inches, the intensity at 6 inches would be four times greater than that at one foot. Therefore, at 6 inches, the intensity would be:

240 mR/hour × (12 inches / 6 inches)² = 240 mR/hour × 4 = 960 mR/hour.

Now, to find the total exposure over 20 minutes, we need to convert the exposure rate from hours to minutes. Since there are 60 minutes in an hour, we can divide the hourly rate by 3 to find the rate per 20 minutes: