Ron Kean wrote:
> I think that a matter-antimatter bomb would exhibit the same efficiency
> (energy per unit mass) regardless of size. A single proton meeting a
> single antiproton would release the same amount of energy per gram as
> would a larger matter-anti-matter sample.
So far as energy production is concerned that is correct. The containment system will tend to consume a larger portion of the bomb's mass as it gets smaller, but that's just an engineering problem - I wouldn't be surprised if someone found a way around it.
Antimatter devices are possible at any scale you want to use. However, really small ones (less than about 0.1 kT) won't make an explosion. That's because matter-antimatter reactions release their energy as high-energy gamma radiation, which can penetrate large amounts of normal matter before being absorbed. Thus, the energy of the bomb will always be spread over a certain minimum volume of space - you can't make an antimatter bomb that creates small explosions. If the bomb doesn't put out enough energy to power a big explosion, you end up irradiating the area and heating it up a bit instead.
So, antimatter devices would be a major threat. The delivery vehicle can't actually be nanoscale, but it could probably be as small as a dust mote and still carry an effective weapon.
Billy Brown, MCSE+I