Final answer:
No projectile enters the chamber when unloading an unfired round from a gun-type fission bomb, as the device has already been detonated. Instead, this type of bomb uses two subcritical uranium masses and a neutron source initiator, creating a supercritical mass that is maintained momentarily for energy release.
Step-by-step explanation:
When discussing the unloading of an unfired round, the question appears to be referring to the workings of a firearm, not a nuclear weapon. However, since the provided information mentions a gun-type fission bomb, let's clarify that the principle is not the same as for regular firearms. In the context of a gun-type fission bomb, no projectile goes into the chamber after the bomb has been fired because the device would have already been triggered, releasing its energy. However, the initial setup includes two subcritical pieces of uranium (235 U) that are brought together to create a supercritical mass, initiated by an explosive charge. A neutron source initiator is present in the design, which introduces neutrons to start the chain reaction at the optimal moment, leading to the bomb's detonation. The energy yield from such a bomb depends crucially on the mass of uranium and the time the supercritical mass is maintained before the device disassembles itself.