I can’t answer that (I mean I don’t know, not that I can’t say), but Taylor indicated that there were feasible designs for which the entire ‘physics package’ could be held in the palm of a hand, which implies a core not much larger than a golf ball at most. Whether such designs were ever tested is uncertain. Such devices were never (to public knowledge) fielded, nor is it clear what use they’d be. (The notion of using nuclear weapons tactically is laughable at best, and frightening at worst.) As I said, Taylor was really interested in minaturized nuclear devices both out of his own intellectual curiosity and as propulsion bomblets for an ORION-type rocket.
Unlikely. Compact, efficient nuclear devices require the explosive containment method, and the implosion has to be shaped and time just so in order that the wavefronts don’t interfere with each other and cause an unevent compression. There were some urban legends about a gun-type californium bullet that would explode as suggested but it is unlikely–to a point of absurdity–that such a device could be made to work. Even if one could fabricate enough Ca to make a bullet (and use it before it decays out), and somehow form it into a subcritical shape that would deform to supercritical, it’s unlikely that it would explode efficiently. More than likely it would either deform irregularly (as bullets tend to do when they impact a hard surface) and just give off a lot of gammas but not literally explode, or it would explode prematurely, blowing off most of its mass without reacting. Again, the value of such a weapon is unclear; it’s too big for covert use, too small for effective battlefield use, to unstable to store very long, and undesireable from a proliferation standpoint. (Can you imagine trying to secure such a thing, or tracking it down if stolen?)
[Sci fi nerd mode] It’s called a Slaver Disintegrator, and since GP hulls are made of a single artificially strengthened molecule ( by a microscopic generator in the hull ), the logical assumption is that the strengthening field/effect overpowers the disintegrator. [/scifi nerd mode]
And again, the devil’s in the details. That word somehow is a biggie. A matchbox-sized lump of neutronium masses about as much as a battleship. But the surface gravity of a large object made of neutronium is in the thousands or millions of gravities. So by the time you have successfully dug out a lump of the stuff (left as an exercise for the student), you’ve got something that’s harder to lift than, at least, all the battle fleets of the world put together - and when I say “harder”, I mean “by several orders of magnitude”.
Slight nitpick on a previous comment… to get a chain reaction, you only need a critical mass, not a supercritical mass, although in practicality most packages end up being supercritical.
Subcritical mass = not enough stuff
Critical mass = enough stuff
Supercritical mass = more than enough stuff
To nitpick the nitpick - a critical mass is where the neutron generation rate is exactly equal to the neutron escape rate. So yes, you get a (barely) sustainable chain reaction, but you don’t get an explosion. It just ticks along, slightly warm, and spitting out neutrons.
You need supercriticality to get a boom, and the greater the degree of supercriticality, the more efficient the bomb.
