The Limerick Nuclear Power Plant, located on the Schuylkill River, a tributary of the Delaware River in Pennsylvania, USA, was scheduled to begin operations on December 22, 1984, after a long construction period. Three weeks before the plant’s opening, a radiation detector was installed at the entrance used by employees commuting to work. On December 2, shortly after the detector was installed, an alarm sounded as construction engineer Stanley J. Watras passed through it on his way to work. The mystery was finally solved when the plant’s radiation safety officers visited Watras’s home and discovered the radioactive material.