Demon core from Fat Man/Little Boy

NB - “Neutrons” was right - plutonium, like U235, will fission when hit by a neutron and in the process produce more neutrons to do the same to other nuclei, hence the chain reaction. The full answer would take longer. :slight_smile:

Moderator Note

Let’s not have any intentional misleading in GQ, please. That comes off as trolling or intentionally being a jerk.

No warning issued.

The short answer is no. Raguleader pretty much covered it. More detail here:

That implosion is the really difficult part. The plutonium pit is surrounded by high explosive arranged in a very specific configuration, with detonators placed at very specific locations on the outer surface. The electronics are designed to trigger all of the detonators with exceptionally precise timing. If the timing is off, then the pit is not squeezed on all sides simultaneously; it just gets displaced toward whichever area detonated late. So if a crash happens to somehow trigger some of the high explosive on one side of the pit, you won’t get a nuclear detonation; you’ll just shoot the pit out to the other side.

In addition to fissile material being hard to come by for the average terrorist, the technology required to turn that material into a nuclear weapon is also deliberately hard to come by.

I’ll incidentally note that the origin of John Cusack’s bomb design diagram in Fat Man and Little Boy has just been fingered.

There is an excellent book “Oppenheimer shatterer of worlds” by Peter goodchild, it was released in conjunction with a BBC series about Oppenheimer. It has some excellent discussions of the experiments and SNR of the physics of a nuclear bomb

Pardon my layman ignorance, but if the core was emitting neutrons, and every atom nucleus has a finite number of neutrons, then would a core that has gone critical eventually deplete itself of neutrons, leaving only protons and electrons behind? And with “neutron reflectors” - are the neutrons really being spat out by the core and flying out and striking the reflector?


PU-239 emits neutrons because it undergoes spontaneous fission - an occasional atom decides to split into smaller pieces, and the neutrons are left over. If one follows this chain of decay, it eventually leads to Lead. And Lead has lots of neutrons in it.

ETA: Yes, the reflectors are designed to re-direct (bounce) neutrons back to the core, reducing critical mass.

Yes, radioactive materials decay over time (it will never “run out of neutrons”, but it will run out of Plutonium).

The half life is about 24,000 years, so it’s not going to "run out’ on human time scales.

However, the radioactive decay is a pretty big component of the aging process of the core. It releases gas which can cause bubbles to form. The buildup of fission products can change the material properties of the core.

Not yet mentioned, but no decaying nucleus will ever spit out all its neutrons, leaving only protons and electrons behind. To do that it would have to fission down all the way to hydrogen (the only no-neutrons element), and that doesn’t happen.