What would the exposure rate at 2 m from a source be after one half-life with 2 HVL shielding, if the initial radiation level at 4 m is 200 mR/h?

To determine the exposure rate at 2 meters after one half-life with 2 half-value layer (HVL) shielding, we can break the problem down into two parts: calculating the exposure rate after one half-life and then applying the effects of the additional shielding.

Starting with the initial radiation level, which is 200 mR/h at a distance of 4 meters, the first task is to calculate the exposure rate after one half-life. The concept of half-life indicates that after one period, the intensity of the radiation will reduce to half of its original value. Therefore, after one half-life, the exposure rate would be:

200 mR/h ÷ 2 = 100 mR/h

Now, addressing the second part regarding the distance change and the effect of shielding. You are measuring the exposure rate at a distance of 2 meters, which is closer than the original 4 meters. The exposure from a point source decreases with the square of the distance from the source (inverse square law).

When moving from 4 meters to 2 meters, the factor of distance change is calculated as follows:

(4 m / 2 m)² = 2² = 4

This means that the exposure rate will increase