Searching for a lost radioactive source in a mining-milling facility

The mining-milling facility in question has a radioactive level gauge installed at the beginning of its conveyor-belt system, used to turn it on when the run-of-mine ore reaches the chemical plant. The gauge was not in use when the incident occurred (radioactive source installed, detector and associated electronics not installed), the conveyor-belt being controlled manually. During a routine inspection, a maintenance worker found the inner part of the gauge's lead shielding on the floor. Since he knew that equipment was 'dangerous', he called a technician supposed to know how to deal with it. The technician monitored the fallen piece, found no activity and concluded, erroneously, that the radioactive source was inside the shielding (actually, his detector was not working). The fallen part was put in its place. All this happened in a Saturday, October 1st, 1994, beginning of a long weekend, so the occurrence was only reported to the responsible for the radiation protection in the following Tuesday. (author)