The smallest nuke available (W80) is about 300lbs and 31.4 by 11.8 inches. It’s more like a footlocker than a suitcase.
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The Davy Crockett is a Nuke Warhead designed to be shot from a recoiless rifle and was developed in the late 1950s
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 selectable yield equivalent to 10 or 20 tons of TNT (very close to the minimum practical size and yield for a fission warhead). A total of 2,100 being made.
THAT was more than half a century ago. A decade before putting a man on the moon. Before Personal Computers, before Microwaves and Cellphones. The size of a nuke now is so small you can fit one anywhere.
51 pounds in the 1950s = x in 2011
I didn’t mean to imply that the W80 was the smallest nuke ever, just that it is the smallest currently available in the US arsenal.
I don’t believe the laws of physics permit a warhead to be miniaturized as you suggest. A pure fission plutonium only weapon still has to have about 8kg of Pu in order to even go boom. The MK 54 to which you refer had about that and only had a yield of 10-20 tons of TNT, about 1/1000 of the Hiroshima bomb, or alternately five OKC bombs.
If you’re just looking for a dirty bomb, a couple hundred grams of plutonium and an OKC size conventional explosive will contaminate a city.