This is a thermonuclear weapon, lodged in a field in North Carolina where it landed after falling from crashing B-52 on January 24, 1961. Some new documents detailing the history of the Goldsboro Incident were declassified this week.
Besides information the history of Goldsboro and several other near-disaster, the documents focus on problems with nuclear arsenal safety during the Cold War. The documents particularly focus on issues with weapons design. At Goldsboro, for instance, the weapons ended up armed (increasing the risk of an actual detonation) because the manual arming switch was designed in such a way as to allow it to turn itself on in response to the force of the plane crash.
The documents also discuss the risks of "sealed-pit" weapons, which were designed with the plutonium or uranium core already sealed into the warhead — unlike earlier designs that required operators to insert the nuclear material when the bombs were ready to be used. The sealed-pit design greatly increased the risks associated with lost or accidentally dropped bombs, as in the case of Goldsboro.