Antimatter contamination?

[Professor Tanhauser]

Ok, here's a question I guess most people here can deal with handily: Does antimatter reactions with matter produce fallout or other kinds of radioactive contemination?

Assume a typical mad scientist succeeds in creating a large amount of antimatter. (HA HA! The Fools! They laughed at me! Now, they shall tremble!) He then sets it up as a bomb in a remote area and detonates it as a show of his power and what will happen if the worlds does not meet his demands.

Ok, now is there any radioactive fallout or residual radiation left over from this? I'm not sure as most nukes leave fallout from the amount of fissile matter in the fission trigger, even if the atoms get stripped of their electrons the nuclei are still radioactive, after all.

But what about an antimatter reaction that involves no radioactive matter? WOuld it leave radioactivity behind?

For that matter, assume another mad scientist invents a laser pumped fusion bomb that doesn't use a fission trigger but fusions deuterium by laser pulse. Would that create fallout or be a clean WMD?

[swansont]

It depends on the antimatter used. electron/positron annihilation will produce gammas, none of which will exceed 511 keV, which is probably not enough energy to cause activation (cause to become radioactive) of anything they hit — for a gamma to knock out a proton or neutron, possibly producing a radioactive nuclide, will require several MeV.

If you use something more massive, though, this might occur. Proton/antiproton or neutron/antineutron will produce gammas of almost 1 GeV, and possibly lower-mass particle/antiparticle pairs that will have significant kinetic energy. These could cause activation.

Also, it's possible that when the annihilation starts occurring, not all the material interacts immediately, and gets accelerated by the explosion. So you might have some very energetic neutrons or protons flying about, which could also activate materials.

[astromark]

At this level you could undertake to explain the subject a little better. I understand critical mass and radiation. At a very basic level. This subject is fascinating as from this research could come the way forward. How much energy is released in the anti mater and mater collision. what is known about this science. Should I run and hide now or can you help me learn what is actually happening here.

[neilzero]

My guess is there will typically be a surplus of matter, plus some delay in the last of the antimater reacting in a practical anti-matter bomb.
I think one neutron in a chlorine atom might be annialated by an anti-neutron. If this was a chlorine isotope with atomic weight 37, it is now the radioactive chlorine isotope (atomic weight 36) with a half life of 310,000 years. This emits a positive beta, a negative beta and an EC. I don't know the meaning of EC. Neil

[swansont]

EC = electron capture. Proton captures an electron and becomes a neutron and a neutrino.

———

There's no critical mass for antimatter; it's not a chain reaction. Antimatter will tend to annihilate with matter, converting the mass, usually into gammas. The ones you get from e-e+ annihilation don't have enough energy to knock a particle out of a nucleus and make it (possibly) become radioactive. For the more massive particle, you probably will. Or other reactions could occur.

[antoniseb]

Swansont's answer is basically right. If the mad scientist somehow had a few kilograms of positrons captured in a magnetic bottle, and then let them go, the energy released would be quite large, and there would be lots of non-radioactive fallout. There would also be a lot of corrupted molecules potentially creating dead or mutated life, and or biochemical toxins. It is also possible that enough energy could be released that some nuclear interactions could happen in the shock wave as to cause some strange short-lived isotopes, but probably not many.

If on the other hand, your mad scientist released several kilograms of solid (very cold) anti-Hydrogen. The gamma rays released would be enough to alter the nuclei of the atoms nearby, and create a nasty soup of strange short-lived elements in the material blasted up into the atmosphere (from which it would later fall out).