If the exposure time for a 2220 GBq (60 curie) Ir-192 source is 2 minutes, how long would it be for a 1110 GBq (30 curie) source?

To determine the exposure time for a 1110 GBq (30 curie) Ir-192 source, we can use the inverse relationship between the activity of the radioactive source and the required exposure time. If the activity of the source is halved, the exposure time doubles in order to maintain the same dose to the film or detector.

In this scenario, the initial source has an activity of 2220 GBq (60 curies) and requires an exposure time of 2 minutes. When the source's activity is reduced to 1110 GBq (30 curies), which is half of the original activity, the required exposure time must also increase to provide the same amount of radiation to the film or detector.

Since the activity has decreased by half, the exposure time needs to increase accordingly. Therefore, doubling the original exposure time from 2 minutes leads to an exposure time of 4 minutes for the 1110 GBq source.

This approach of understanding the relationship between source activity and exposure time is critical in radiographic testing, where maintaining consistent image quality often relies on balancing these two variables effectively.