If you wanted to make the smallest nuclear weapon possible (whether fission or fusion, although I’m guessing fusion would require something far bigger), what is the physically smallest it could be and still function?
I don’t know enough about physics to know how much force the gun or implosion designs have to have in order to detonate the bomb.
Can you make something with a 3 foot long barrel and make a gun type design, or are explosives powerful enough to trigger a nuclear explosion in something that small non-existent?
I’ve heard the USSR and US built nuclear weapons about the size of small refrigerators, but suitcase nukes were never verified. I don’t know if they were invented but if they were it isn’t like the US and USSR would admit to making them anyway.
The M-388 round used a version of the W54 warhead, a very small sub-kiloton fission device. The Mk-54 weighed about 51 lb (23 kg), with a yield equivalent to somewhere between 10 or 20 tons of TNT — very close to the minimum practical size and yield for a fission warhead.
The Davy Crockett is probably near the limit for a uranium or plutonium-based device, but you could in principle get much smaller with other, more exotic, isotopes. IIRC, you could make a nuclear hand grenade using americium (or maybe it was californium).
The W80 is a cylinder about 1 foot in diameter and 2.5 feet long, yield up to 150 kt. The W87 and W88 warheads fit inside cones less than 2 feet in diameter and 6 feet tall, with yields approaching 500 kt. So you can build “full-sized” (10-20 times more powerful than the Hiroshima/Nagasaki bombs, able to destroy city-sized targets) thermonuclear warheads much smaller than refrigerators. They weigh hundreds of pounds however, so you’d need at least a dolly (or maybe a forklift) to transport them. Keep in mind that these are fusion bombs, which basically have a fission bomb as their primary.
I agree that the W54 is probably about as small as you’ll be able to get a nuclear warhead. In the Wiki article linked above it’s noted that they required extensive testing (more so than any warhead before them) to make them reliable. Any smaller and you’d be better off using conventional explosives for their predictability alone.
I think the smallest nuke was an air to air missile, like either the Genie or the Falcon. I heard the suit case nuke was a poor translation, the russians meant something that looked like a steamer trunk, which read suit case in english.
It also occurs to me that the SADARM was carried by 10th special forces personal on their back, but it would be around .5kt or so.
Suitcase nuke; for the US it was called the SADM (Special Atomic Demolition Munition). Modified W54. Davy Crockett, Falcon AIM-26A missile, and the SADM. Not really a “suitcase” but a big backpack. The W48 155mm artillery shell was around half the diameter for the nuke package compared to the W54 in the Davy Crockett (<6’ vs. 11’). See the Wiki for the W54 and and W48 munitions. Note that a design capable of fitting in a 105mm artillery shell was considered possible.
There isn’t a sharp demarcation line for how small a nuke can be; rather you get a dropoff curve for the yield as the weight of the package decreases and the efficiency of the reaction drops. It becomes a matter of how small a “fizzle” you consider a nuclear explosion. The Davy Crockett was really sort of intermediary between a tactical nuke and a “dirty bomb”; it fizzled just enough to produce a deadly pulse of immediate radiation and scatter radioisotopes across it’s target area.
I read about a theoretical weapon made for sniper rifles using californium. Californium (it said) has a very low critical mass, and it was suggested that you could make a bullet with two pieces of it in the tip, separated by something that absorbs neutrons. The barrier is destroyed on impact, and the shape of the bullet forces the two pieces of californium together.