In a few movies (Broken Arrow, True lies) nuclear weapons are portrayed as having “arming codes” to activate them. Nukes are actually triggered by the detonation of conventional explosives, so it should be possible to open them up and hot wire the detonators in the absence of arming codes.
The only way I can think of to prevent this is to booby trap the nukes, blowing the casing apart and scattering the nuclear material if anyone tries to open them. Is this done?
If it isn’t, I’ll take a hacksaw to this thing…
SOOMA, one of the trickier bits involved in making a nuclear bomb is getting the conventional explosion to go off just right. The (conventional) explosives are used to squoosh the radioactive material into a space that it would not naturally be able to occupy, resulting in a spectacular light show. To get the compression right, they need to exert force (the force coming from the conventional explosion) equally on all sides. Not too easy if you are dealing with a spherical charge. This is why the triggers are difficult to engineer (didn’t Iraq get caught trying to buy a set of triggers a few years back?) Unless the pressure from the initial explosion is perfect, you will not initiate the chain reaction that makes nuclear weapons so much fun.
So I can’t speak for the voracity of arming codes and whatnot (though I believe all bombs really do have those red LED clocks on them) but hotwiring the trigger mechanism without the requisite electronic signals is unlikely to get you much of an explosion. Well, not that I’d want to be standing in the same room when it went off mind you, but I don’t think I’d mind being in the museum down the street ogling the artwork.
I think Rythmdvl has it right. If you don’t get a good implosion from your trigger charge, a fission bomb would fizzle. But you still get a fair sized bang and a scattering of Plutonium (which is one of the most poisonous substances known, aside from being radioactive).
If we’re talking about thermonuclear devices (ie Hydrogen bombs) things become a bit more complex. The conventional charge triggers a fission explosion, which is then used to initiate a fusion reaction. So you could have a problem in the fusion reaction and get a “dud” that is still a much bigger bang than I would want to be within a hudred miles of. 
In addition to the explosive used to cram everything together just right I thought the whole thing had to be bombarded with something (electrons? protons? neutrinos?..not sure which) to help kick off the fission reaction (fission bombs being used in both Hydrogen [fusion] weapons as well as Atomic [fission] bombs). Without the ‘arming’ codes even if the conventional explosion goes off perfectly you won’t get much more than that without the added nudge of (say) electrons whipping through the chamber at the same time and that may also be controlled electronically from the arming mechanism.
Robert Heinlein wrote a story The Long Watch in 1949. It’s a science fiction story in which the hero is confronted with the problem of sabotaging some nuclear bombs so they can’t be repaired. According to this story, the two uranium halfs must be mirror polished so they meet properly to trigger the explosion, so the hero physically smashes the faces so their finish is damaged.
Jeff_42, you may be thinking of the “Neutron Flood” of a chain reaction. Fission occurs in two ways. First, radioactive atoms spontaniously decay (thus Half Life, Carbon 14 Dating, ect). Secondly, they can split when a loose Neutron slams into their Nucleus.
In a critcal mass, the atoms are packed so tight that some of the left over Neutrons from a spontaneous decay split other atoms. Some of their left over Neutrons split more. And so on and so on. Speed this process up and KABOOM!
That’s why nuclear reactor cores contain large amounts of “moderator material” (for some reason I’m thinking it’s Graphite) in addition to the control rods.
Jeff
You are correct. The explosives have to go off exactly right to compress the material enough so that it can go BANG. It does not stay in the highly compressed state very long. The naturally occurring fission heats it up, causing it to expand, and fissle [blow apart] instead of BANG. You need to have enough free neutrons available while the material is highly compressed before you get a BANG. There is a small chance that this could happen naturally. [You could also try increasing the amount of explosives to try to keep it compressed longer.]
Each weapon uses a trigger, a separate neutron source. This is inserted to arm the weapon. Then you can use the codes to make it go BANG.
You can find out almost everything you always wanted to know about nuclear weapons, including a university-student level FAQ about the physics of the ‘packages’, at this website:
http://www.fas.org/nuke/hew/
Enjoy.
Bill
Thanks to Willie & Starfish, I was ignorant of needing an external Neutron source.
I assume the “source” is engineered as a insertable assembly (for safety, at least)?
Something I learned on this board: Since when has critical mass been so easy?
DHR
Interesting stuff! I guess I can’t just connect a truck battery to all the detonators in parallel and use an alarm clock as a timer switch…
However, I do have everything I need in my stolen nuke. I have a nice spherical core. I have the conventional explosives arranged in lenses or whatever they use these days to get a spherical implosion. I have the ultra-fast detonators which go off in nanoseconds rather than microseconds. I have the neutron generator. I have the battery/generator which makes it all go. And I have a control computer which I can’t use, but it has outputs to the relays/transistor switches/whatever which fire the whole lot up. If I were an Unfriendly Foreign Power or an Evil Genius, I’m pretty sure I could get this thing to go bang, given time to figure it out.
If I’d BUILT the bomb, I’d rig it to trigger ONE of the detonators if it were opened by unauthorised persons. I guess this would leave a mess and a squidged ball of plutonium, which would take a whole Manhattan Project’s worth of work to set off.
You might find Tom Clancy’s The Sum of All Fears to be an interesting read. Terrorists find an unexploded Israeli (!) nuclear bomb, hire out of work East German physicists to take the plutonium core and fit it into a new, workable bomb of their own–which they explode in Denver, at the Super Bowl.
DHR