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Underground > Laboratory >

How hard is it to detonate a Nuclear Bomb?

09:30 / 17.04.03

I was watching Broken Arrow last night and at the end there is a huge explosion with a Nuclear Bomb at its centre. The bomb remained undetonated. This quite often happens in Hollywood films when a nuclear bomb will be 'intact' or the core isn't breached after huge explosions. Is this true or is this bollocks? Is it really that difficult to detonate the nuclear part of the bomb?

Somehow I don't think they'll be covering this one on Hollywood Science (UK BBC2 7:30 Weds)

Dances with Gophers

11:53 / 17.04.03

Yes, it is actually quite difficult to produce a nuclear explosion and it's quite easy to knock out a nuclear missile without causing a nuclear blast. Someone once explained the physics to me, but it went over me head.

11:55 / 17.04.03

OTTOMH, yes. The proncip`les behind making a nuke are simple, but the engineering problem is quite tricky. You have to get a critical mass together - roughly in the same place won't work and exploding it doesn't help per se. As I understand it, a nuke works by having two pieces of the radioactive material which are then forced together in a controlled explosion. Get this wrong and you don't get more than a pop.

14:53 / 17.04.03

Yeah, I think you have to aim two explosions towards each other with fissile material in the middle, so it slams in on itself.

Actually, no, there are two ways to skin this cat:

THE FIRST DESIGN of a nuclear weapon in the United States was a gun-barrel assembly, in which two sub-critical masses of very highly enriched uranium (HEU), were brought together by normal artillery propellant in a short gun barrel into a single over-critical configuration. (Criticality defines the minimum amount of a fissionable material in a particular configuration and density capable of a self-sustaining chain reaction).

The second type of fission weapon is the implosion assembly, in which a high explosive (with a much faster detonation speed than the propellant used in a gun-type weapon) compresses fissile material so that it reaches a super-critical mass. Less fissile material is required for an implosion assembly because the critical mass varies inversely as the square of density

Hiroshima was "gun," Nagasaki was "implosion."

This site has nice diagrams.

tom-karika nukes it from orbit

17:15 / 17.04.03

How good does the join between the pieces of nuclear material have to be?

I know that powerstation-grade Uranium is stored in small cubes or pellets of around 1/10th of the critical mass which are separated by at least a centimetre of lead, in order to keep the chances of a chain-reaction to a minimum.

But looking at the mechanims used in actual bombs, the two pieces of nuclear material are slammed into each other pretty hard, heated at the same time.

Why can't they just use a spring-loaded or solenoid mechanism?

(Thought - atomic mouse trap? mouse takes cheese, critical masses moved into place, no more mouse. Or planet for that matter.)

17:44 / 17.04.03

Back to the abstract, though, a Teller-Ulam (Ulam-Teller?) type bomb in a conventional explosion would go to pieces rather than go critical.

19:59 / 17.04.03

I misread the title. I thought it said How hard is it to donate a nuclear bomb. I wondered if you had a spare one going.

17:26 / 18.04.03

I don't think a spring or solenoid can generate enough force. Basically, you're smushing the uranium or plutonium together so hard, its molecules go all bumpy-bumpy.

Elijah, Freelance Rabbi

17:47 / 18.04.03

early nuclear bombs work on the same ideas as the sun, fission
check it

basically, uranium 235 has as man electrons as it can hold without vibrating apart, 235 actually.
when you fire a neutron at this fast enough and hot enough, when the uranium gets hit it splits into 2 "lighter" uraniums, firing off extra neutrons, causing a chain reaction and releasing insane amounts of energy.

follow the link for lots more info

18:26 / 18.04.03

As far as my understanding goes, it might be possible as long as the bomb is exploded in a way that the uranium/plutonium doesn't come together as critical mass. The problem is usually TNT is used in fission bombs to drive wedges of uranium together to create a critical mass, so if you started as explosion, it would trigger the TNT.

Who's your Tzaddi?

20:09 / 18.04.03

uranium 235

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Brrr.

23 Enigma!

Number 5!

≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞≡∞

Elijah, Freelance Rabbi

20:09 / 18.04.03

depending of course on the type of detonation, if it was an implosion type and the explosives werent triggered with the right timing you would spray radiation everywhere, but no mushroom cloud i would think, same for the gun barrel type, if the explosion broke the barrel than no boom

16:20 / 19.04.03

Elijah: the sun is fusion, not fission.

Phaedrus: As far as my understanding goes, it might be possible as long as the bomb is exploded in a way that the uranium/plutonium doesn't come together as critical mass.

Yeah, pretty much. If the explosion blows up the casing, there's not enough focused force to wham the fissile stuff together. Basically it becomes like a big "dirty bomb."

So what Elijah said.

Elijah, Freelance Rabbi

23:46 / 19.04.03

Elijah: the sun is fusion, not fission. riiight, like we are supposed to believe anything a tabloid writer says :-P

yeah, i mixed it up...