If a 1850 GBq (50 curie) Ir-192 source requires 4 minutes of exposure time, how long would a 925 GBq (25 curie) source require?

To understand the time required for exposure to a 925 GBq Ir-192 source based on the known exposure time for a 1850 GBq source, it's important to recognize that exposure is inversely proportional to activity. This means that as the activity of the source decreases, the time required for an equivalent exposure increases.

In this case, the first source with an activity of 1850 GBq takes 4 minutes for exposure. The second source has half the activity at 925 GBq. The relationship between activity and exposure time indicates that if the activity is halved, the exposure time will need to be doubled to achieve the same dose.

Calculating this, since the 925 GBq source is half the activity of the 1850 GBq source, the time required for exposure would be:

4 minutes x 2 = 8 minutes

Thus, the 925 GBq source requires 8 minutes to provide the same level of exposure as the 1850 GBq source did in 4 minutes.