24 February 2014
A Manhattan Project medal
Individuals who worked with the Manhattan Engineer District for more than one year were awarded a silver medal. Those with less than one year's service received a bronze medal. I could find no record of anyone receiving gold medals.
More information at Oak Ridge Associated Universities (whence the photo) and at the Atomic Heritage Foundation, which is "dedicated to the preservation and interpretation of the Manhattan Project and the Atomic Age and its legacy."