Is it possible to build a really small hydrogen bomb? or any nuclear bomb for that matter? I’m not talking size of device here, I mean in terms of output. Is there a minimum threshhold that must be achieved for a bomb to boom?
Yes. I refer you to the missing Russian “suitcase bombs”. Scary? You bet!!!
http://boards.straightdope.com/sdmb/showthread.php?threadid=8478
Peace
LIONsob (formerly known as The LION)
Yes…there is a lower limit on the size of a nuclear bomb. Not the physical size of the bomb but rather the yield (call it the boom potential).
This is commonly known as critical mass. For a basic A-bomb using Uranium I believe the critical mass is around 52 kilograms (around 115 pounds).
115 pounds of Uranium sounds like a lot but remember that Uranium is very dense and heavy (heavier than lead) so it is possible to put the bomb in a large suitcase. That said it would take a fairly strong person to lug the dang thing around (115 pounds plus all the other goodies needed to make the bomb work…say 150 pounds at a minimum although that’s a WAG on my part).
For an H-bomb (hydrogen bomb) remember that for it to work you make an A-bomb to cause the detonation. H-bombs work using fusion, A-bombs use fission. For an H-bomb to achieve the luicrously high pressures and temperatures necessary to cause fusion to start you need the temperatures and pressures found in the center of an A-bomb explosion to make it work. Thus, an H-bomb is going to be even bigger than your smallest A-bomb since it really is an A-bomb plus H-bomb.
If you have less than the critical mass required for explosion the material can still be dangerous. It will kinda start its chain-reaction releasing all sorts of nasty radiation. While the whole thing may not go BOOM it can still be quite lethal to anyone unlucky enough to be standing nearby. IIRC this is what happened to those workers at a Japanese nuclear plant. They dumped a near critical mass of nuclear material together and it did its little flash thingy (sorry…don’t know the technical term) on them giving them near lethal doses of radiation poisoning.
Remember that shaping is an important consider in the making of nuclear bombs – if the charge is the wrong shape, the detonation might not work well enough to cause critical mass. So while a suitcase bomb might be possible, it may be more reliable to develop a box-the-new-TV-came-in bomb.
Here is a couple of sites that might help answer your question.
http://www.ask.ne.jp/~hankaku/english/chronotbl.html
Peace
LIONsob
I don’t know about the reliability of this source, but this article mentions that the Iraqis recovered 27 kilograms of HEU from the Osiraq breeder reactor that was destroyed by the IDF in 1981. The author of the first article on that page considered that to be sufficient to produce one very-low yield nuclear weapon.
Oops. It seems as if the Russians may have misplaced 100 or so suitcase nukes. Again, take this with a grain of salt.
This article notes that while the U.S. has developed a fairly compact portable nuke, it is possible to make them much smaller than what we currently have. A 105mm nuclear artillery shell is considered feasible. That’s a diameter almost small enough to fit in a blueprint tube.
Here’s a pic of the Davy Crockett. The business end is that cute little blimp-looking thing. Big, but very close to man-portable.
I don’t know if I’m answering the worng question here as everyone seems to be focusing on suitcase bombs and the like. I read the OP to be asking how small of a BOOM a nuke can make regardless of its physical size.
Assuming I’m on the right track and you want an answer on the smallest explosion a nuke can make then some of the links provided by LIONsob are informative as well as some of Sofa King’s links.
From what I can gather the smallest bang you’ll get out of a nuke today is 1 kiloton (1,000 tons of TNT). Not enough to take out a city but easily enough to wipe the Kremiln or Capitol Hill off the map.
That said it looks as if work is progressing on fourth generation nuclear weapons.
(highlighting mine)
Hope that helps.
Correction to my quote above.
I mispelled ‘Kremlin’ and, more importantly,
The ‘superlaser’ mentioned has a power output of 10[sup]19[/sup] W/cm[sup]2[/sup]
That’s a BIG difference from 1019 W!
There are two ways to create very small atomic explosions. The first way is to reduce the efficiency of the bomb by reducing the degree of supercriticality. This allows you to make a nuclear explosion as small as you like.
The yield of a fission bomb depends upon the number of nuclei that split during the chain reaction. To get a reasonable yield, you need a supercritical mass, usually 2-3 times the critical mass. If you have a barely critical mass, you can get an explosion no more powerful than a firecracker, if that’s what you’re after. You also get radiation and a horrible local contamination problem. For more details, see my reply in:
http://boards.straightdope.com/sdmb/showthread.php?threadid=33654
The easiest way to create physically small bombs like this is to use slightly subcritical masses and weakly compress them into slightly supercritical masses using explosives.
This approach, combined with neutron reflectors, allows bombs physically weighing 15-30 kg which will fit into a suitcase and yield up to one kiloton explosions. Not bad, but you’re not going to be lobbing nuclear grenades at tanks any time soon!
There is a possibility of making these things physically smaller by using highly fissile transuranic elements. Californium 251 offers the possibility of nukes physically weighing around 2kg with yields of 10-20 tons. Thats getting into the ballpark for mortar shells and shoulder launched rockets. Hideously expensive though.
I vaguely recall reading a report long ago about nuclear bullets. The story was that the US test fired bullets containing heavy fissionable elements like americium. The bullets were designed to implode on contact with a hard surface and compress the americium to critical mass, with a low yield nuclear explosion.
IIRC, this isn’t a really practical weapon, the fissionable isotopes of americium have such short half-lives that you pretty much have to fire it as soon as the bullet is made. And if your bullet doesn’t hit something hard and implode, its a dud. It has to hit something hard like concrete, you’d hate to shoot an expensive packet of rare elements and it ends up sunk in the mud somewhere. Maybe what you need is a nuclear machine gun! You’d be sure to hit something…
Anyway, pocket nukes are really a moot point. We have all the adustable sub-kiloton weaponry we need. Fuel Air Explosives have been called the “poor man’s nuke” and are cheap and destructive. The russians used FAE weapons in Chechnya against cities and reduced them to rubble in hours.
I recall that after the Gulf War, there was some speculation that if we had had effective “mini-nukes” or “micro-nukes”, we could have utilized an effective “bunker-buster” weapon and taken out Saddam Hussein with no muss, no fuss. Just a WAG, but I’d speculate that’s one reason low-yield nuclear weapons would still be regarded as having an advantage over fuel air explosives.
When I first posted this, I was thinking of the problems so far encountered with developing a fusion power generation system. And it occurred to me, why can’t they just build a big strong room, set off some small hydrogen bombs in it and have a bunch of water pipes in it that can be heated.
Hence the need for small bombs.
There was a shoulder-fired nuke missile in the '50s…problem was, the range of the rocket was less than the blast radius…the 2-man crew had to dig a trench before shooting so they could dive into it and avoid the blast.
Now that IS an interesting question. For fusion bombs, again theoretically there is no minimum size. What you have to do is take your deuterium-tritium mix and heat it to a few tens of millions of degrees while confining it as a high density plasma. Trouble is, in an H-bomb, this is achieved using a fission bomb explosion. So you have the fission bomb yield as a minimum.
The reason fission bombs are so useful as fusion triggers isn’t so much their total yield as their power - the chain reaction is FAST and the energy is released in a very short time interval. A low yield fission bomb (say, 1 ton) could possibly be used to trigger a secondary, low yield fusion explosion (WAG on my part.) That would be a very inefficient use of the fissile material however, and it would probably make more sense to burn it in a conventional nuclear reactor than to use it as a fusion trigger.
You may already know that your scheme is being worked on on a much smaller scale - it’s known as pulse fusion. Current research attempts involve triggering very small fusion explosions (equivalent to a few ounces of explosive) using a system called “inertial confinement.”
A pellet containing the D-T mix is hit on all sides by immensely powerful lasers, or by electron beams, or by X-rays generated by electron beams hitting a metal target. The surface of the pellet explodes spherically, outwards and inwards, and the D-T is compressed and heated enough to fuse.
It works, in the sense that fusion is routinely achieved this way. However, at the moment the energy extracted is far less than the energy input required for the inertial confinement.
Sorta like a kamikaze nuclear bazooka. 
Source (and more details about the Davy Crockett Nuclear Rifle Grenade:
http://www.brook.edu/FP/projects/nucwcost/davyc.HTM
“implosion fission” means a plutonium device. The main use for these devices was to take out major dams, bridges, tunnels, rail exchanges, or rockslide a mountain down onto the pass, with one single device.
Let’s also not forget enhanced radiation devices, a.k.a. “Neutron Bombs,” low yield H-bombs made deliberately “inefficient” in such a way that more of the energy would fly away as intense radiation rather than as heat and blast.
All these devices ostensibly meant to be used by our gallant boys as a way to slow the steamrolling horde of godless but still meaner and more numerous commie armor pouring in from the east. A lot of the doctrine for use of Tactical Nukes was based on a lack of precision guidance(for the D. Crockett, you found your range with a 37 mm gun) so you had to use a device that would obliterate the target even if it just got close. “Smart” weapons took over for battlefield nukes in many roles.
jrd
Everything you ever wanted to know about nuclear weapons and more at:
http://www.fas.org/nuke/hew
Talks all about critical & supercritical masses, small fission bombs, fission triggers for fusion secondaries, etc…
But not completely unlike the nuclear bomber, which, IIRC, was a one-way mission if carrying a big enough H-bomb. Especially at low-level.
[QUOTE]
*Originally posted by JRDelirious *
**
A deterrent that worked, as evidenced by the fact that we’re all here having this discussion.
Cold War joke:
Q: Define “tactical nuclear weapon”
A: One that explodes in Germany