Joe,
Two reasons why i would ask such a question. First, depending on were you read you come up with several different effective ranges for ir-192. One source I have read says 3", another says 4", the chart above says about 2.5". My shot calculator goes up to four inches. Second, It is extemely time consuming and costly to get a cobalt source. not to mention the entire facility would need to be evacuated due to the locations of the welds. Gas companies dont take it very well when you put the control room inside your barricade. Yes is gives me a 5 minute shot compared to an hour with ir-192, but the company that shot the weld the first time did so with ir-192. I looked at the film and it is good quality film, the only problem is that it was shot to b31.3, and it needs to be reshot to 1104. And who said anything about being an rso?