If the exposure rate at 2 meters from a radiation source is 18 R/min, what is the exposure rate at 5 meters?

If the exposure rate at 2 meters from a radiation source is 18 R/min, what is the exposure rate at 5 meters?

• A. 2.0 R/min
• B. 2.88 R/min
• C. 5.40 R/min
• D. 12 R/min

Answer: (B)

Exposure rate from a radiation source follows the inverse square law: it decreases with the square of the distance. So you scale by the factor (d1/d2)^2. Here, the rate is 18 R/min at 2 meters, and you want it at 5 meters. Compute: R at 5 m = 18 × (2/5)^2 = 18 × (4/25) = 72/25 ≈ 2.88 R/min. That’s the exposure rate at 5 meters.

Exposure rate from a radiation source follows the inverse square law: it decreases with the square of the distance. So you scale by the factor (d1/d2)^2.

Here, the rate is 18 R/min at 2 meters, and you want it at 5 meters. Compute:

R at 5 m = 18 × (2/5)^2 = 18 × (4/25) = 72/25 ≈ 2.88 R/min.

That’s the exposure rate at 5 meters.