I have recently gotten a barium swallow test for my dysphagia. The radiologist said it would pass in about 3 days. The problem is that I would still have it in my system when traveling to the airport. Would this set any alarms off? If so, how do I prove I'm innocent?
No, a barium meal will not set off alarms.
Lots of security places have radiation detectors, and they are set to detect very low levels of radiation. From personal experience they can detect a "radioactive stress test" a few days after it happens.
However a barium meal is not a "radioactive stress test" and is not significantly radioactive, compared to, say, a banana.
If you are X-rayed at the airport, the residual barium might conceivably show up. A letter from your doctor should be enough to ensure you don't actually 'get in trouble' because of it.