I found this item mudlarking on the shores of Brooklyn. According to the Museum of Radiation and Radioactivity, it is a pin that was given to individuals who worked with the Manhattan Engineer District (The WW2 Era name for The Manhattan Project) for more than one year. A bronze pin was awarded to those with less than one year's service.
My pin was made of silver.
I researched and found an article that describes the amount of people who worked for the Manhattan Engineer District and it was a few thousand. It was famously headed by J. Robert Oppenheimer.
On the back of the pin is the name "Whitehead". Individual names were engraved on to the pins.
My grandfather fought in WW2 and this relic is special to me but I also know that there is a lot of pain and suffering associated with it. I remember my grandmother being supportive of the decision to drop the bomb because she didnt want her brother to be killed in an invasion of Japan.