Sorry, but WONG again. True, your Pentium Iv IS fast, in the GHz range. BUT-- it CANNOT be used,by itself, to trigger exploding-foil type detonators, that are used in precision detonators, (look this up,(exploding foil detonator) BTW) , and it needs an "interface', such as an SCR or IGBT or other high-power device. THIS is where the "Delay " comes into play. SCR's and IGBT's CAN handle the current, but CANNOT be counted on, to operate within NANOSECONDS of each other, when switching high-current, high-voltage pulses, as needed to fire the detonators. So, we are back to the old" need an esoteric switch," like a Krytron, which is extremely fast,and which purchase of is also VERY controlled.
And, modern , Small nuclear devices often use an EXTERNAL neutron-generator, a miniature cyclotron, sometimes called a "zipper", to inject the neutrons into the core.As the materials inside of it decay over time, it needs to be replaced on a regular basis, to insure reliability.
Now, I will ADMIT, that an old-fashioned, gun-type nuclear device, which is much bigger,heavier, and needs more fuel(you CANNOT use plutonium, you MUST use uranium, in a gun bomb, plutonium must be "fast fissioned"in an implosion sphere"),would be much easier to construct, but STILL, you need a neutron generator or initiator device, as you descrbed. The electronics to initiate such a gun-type device are MUCH simpler, than an implosion bomb, and THIS would be a more likely worry, NOT a suitcase-type micro-sized implosion bomb, that needs to worry about maintenance of the tritium, neutron generator, firing ckty, batteries,and so on. In such a gun-type device, you need a significant amount of highly enriched U235, however,and THIS is where the terrorists would (hopefully) run into a problem.
All that matters is that the signal arrive at the shaped charges to insure that the compression wave is close enough to spherical to sustain the required geometry. You don't need exploding foil detonators or any of the other crap. If you wanted to make sure your bomb did not go off in the silo or on the bomber, and if you had the resources of a superpower, and if you were deterring other nuclear powers and if you had special needs such as the weapon being able to withstand multiple g's and to go off at a precise altitude, withstand shock waves and high intensity radiation or concussion, then, yeah, you might need some or all of that junk.
Krytrons and exploding foil detonators were not in use during WWII, yet atomic bombs were. I wonder how that could be?