When doing my NIH traineeship, in the new lab, it came to be my turn to do the monthly radiation inventory. When going down the list, while checking the radio labeled nucleotides and labeled reagents in the freezer etc, I came across an entry for 600 Curies of Co 60! Freaking out I immediately went to the PI and told him about this. He laughed and said someone had to be responsible for the campus radiation source and since our lab used it a lot to make feeder cells, we were the lucky custodians of said source. I did get quite the fright though!