It's interesting how radioactive sources are often detected while looking for something else. About 10 years ago, I was pulled into a situation where PET imagi

It's interesting how radioactive sources are often detected while looking for something else. About 10 years ago, I was pulled into a situation where PET imaging patients were setting off radiation detectors coming back into the US at border crossings. Now, it's not unusual for patients who have been given radioisotopes to set off detectors at airports, etc, what was unusual is that PET isotopes usually have very short half-lives. In this case, the patients had been given Rb-82, which has a half-life just over 1 minute. Yet they were setting off detectors weeks after getting PET scans. What was happening was that there was contamination of the isotope. They were getting more than the allowable amount of Sr-82 along with the Rb-82. Sr-82 has a half life of about 25 days. The way that Rb-82 is made, is the pharmacy is provided with a generator or 'cow', which is a bunch of Sr-82 which decays to make Rb-82. The 'cow' is 'milked', which means passing saline through it, and if all goes well the Rb-82 comes out with the saline and the Sr-82 stays in the cow. Some Sr-82 always gets out but usually it is a small amount. Now, Sr-82 is not easy to measure, and the limits are very small. Sr-82 only has a few very low energy gammas. I happen to be an expert in the type of device normally used to measure it (a re-entrant dose calibrator). The QA check used in the clinics was, shall we say, optimistic about the ability to detect it. Here's an article about the situation: https://www.fda.gov/drugs/drug-safety-and-availability/fda-drug-safety-communication-planned-return-cardiogen-82-market-new-boxed-warning https://www.fda.gov/drugs/drug-safety-and-availability/fda-d...