I stumbled upon this wikipedia article on antimatter weaponry.
Being greatly appalled by the sad fact that large sums of money are being wasted on this, I could not stop myself from thinking for a moment about the physics behind it.
If you somehow put together a gram of antimatter and a gram of matter all at the same instant and at high density (so the "annihilation efficiency" would be 100%), would there actually be any explosion?
AFAIK, this would just produce large amounts of gamma photons, neutrino's etc., but there's be very little (anti)matter left to absorb the energy in the form of kinetic energy. In other words -- it would be a radiation bomb. There wouldn't even a flash of light to warn anyone.
Would this indeed be the case? Or am I overlooking something here?
Answer
Have a look at these cross section plots of proton proton scattering and anti-proton proton, where the anti proton has an order of magnitude higher probability of interacting.
It is not true that most of the energy goes into radiation, it goes into creating particles, with an average multiplicity for annihilation at rest of about five charged particles. The interaction is strong and gluon mediated, the photons produced come from pi0 decays, direct photons are a higher order effect.
Thus one gets an "explosion" as this image shows, once one obtains large numbers of such annihilations in a small space
The charged pions will eventually end up as electrons and muons carrying a lot of the kinetic energy of the reaction and a destructive power. The piOs, about 1/3 of the charged number, will give two photons which on average will have enough energy to be destructive when hitting nuclei.
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