# Matter-Antimatter explosion

Was watching Angels & Demons. Obviously the matter-antimatter explosion in that movie was subject to Hollywood. Unfortunately, I don’t remember the supposed yield of the antimatter material. In the book and the movie, if the containment unit had remained in the city, it supposedly would have caused great damage. As it happened, it ended up on a helicopter some distance in the air, exploding, and resulting in a great wind force plus very pretty cloud patterns.

So… what actually happens in a matter-antimatter explosion, especially one the magnitude of which is in the novel/film (sorry I can’t quantify it without help!), either on land or in the air?

For a mass m of antimatter, you get an energy output of 2mc[sup]2[/sup]. The energy release will be very close to instantaneous.

here ya go, the antimatter calculator…

http://www.edwardmuller.com/calculator.htm

if the vial contained 1 gram of antimatter it would be a 42 kiloton explosion, double the size of the Nagasaki fat man explosion.

The calculator is wrong, and you have to multiply all results by two to get a meaningful answer. As the OP-title indicates, the use of antimatter for destructive purposes will be in a matter-antimatter explosion. Matter and antimatter in equal proportions are converted to energy, but the calculator only gives you E = mc[sup]2[/sup], not as I posted above, E = 2mc[sup]2[/sup]

1. A challenge with nuclear weapons design is getting much of the fuel to fission or fusion before it’s blown apart by the explosion. Ref Nuclear weapon design - Wikipedia, the weapons used on Japan actually consumed only ~1% and ~23% of their fuel. The rest was wasted, simply scattered throughout the fireball.

Later designs are doubtless more efficient. But they’re not achieving 100% conversion.

The same issue would apply to a matter/anti-matter explosion. So while the prior posters conversions are correct for the pure physics ideal, the engineering reality would be less. As the residual anti-matter intereacted with the ambient envronment it’d react against the normal matter present, but you’d get a more diffuse FAE-style explosion rather than a point blast. Although on the scale we’re discussing the difference may be practically immaterial. Clearly you’d have a bigger difference for an anti-matter burst in the vacuum of space versus in an atmosphere, under water, or underground.
2. Does anyone have any good info on what the explosion would be like? how do the time constants compare to ordinary fission or fusion? What are the types and energy levels of the daughter products?

Assuming you had both A) a macro-scale supply of some flavor of anti-matter, and B) some way to contain it, how could a naive git’r’done bomb work? e.g. use a magnetic field to slam the reactants together or ???

Why bother slamming reactants together? Unlike a fission bomb, where you want the mass to stay together in order to increase the probability of neutron capture (and hence fissioning), your antimatter will react the same way whether you keep it together or not. The force of earlier matter-antimatter annhilation will propel antimatter into more matter, causing more reaction. blowing your core sample of antimatter apart is actually a desirable goal, because it increases the rate of reaction. And i can’t see an advantage in keeping the region of the reaction contained , as long as it’s not spread over a large area. And I can’t see a gram of antimatter being spread over a large area.

What will be different is that you won’t have solid reaction products from the reaction itself, which will produce lots of photons and particle/antiparticle pairs. And if you set it off near the ground you’ll get lots of activated material (and hence fallout).

I’ll bet someone has looked into the dynamics and products of an antimatter bomb.

I have to do some searching to back this up, but I remember reading here on the dope (perhaps by Stranger?) that matter/antimatter reactions aren’t quite as powerful in a practical sense as one would think because the reaction produces a LOT of neutrinos. Those carry off energy but since they don’t interact significantly with matter, almost all of the neutrino energy dissipates.

And I remember the in terms of mass, the sun converts no more than 3% of it’s matter to energy. So the best fusion reaction we know is 97% inefficient.

But like I said, I have to find cites.

Can anyone tell me where antimatter would come from? If there was any around shortly after the Big Bang, wouldn’t it have likely run into some matter and…well you know. So if there is any around now, where did it come from?

Antimatter can be produced in various high-energy processes (both natural and in laboratories), but all known methods of doing so produce equal parts particles and antiparticles. So you end up wasting at least half of your energy making stuff that you could just gather from the environment, and then you have to separate them out before they recombine.

Of the fuel that the Sun actually burns, about half a percent of the matter gets converted to energy. But then, only about a tenth of the Sun’s fuel will ever get burned at all. When it eventually dies, it’ll still be mostly hydrogen, not helium.

Why quote me with this comment?

It’d be more relevant to the OP, and has nothing to do with the point I was making.

If the difference between pure physics ideal and energineering reality is immaterial, then the physics ideal is correct in both realms.

Even in space I think it likely you’d need so much containment gear you have enough matter for complete matter-antimatter conversion to happen.

I’m more interested in the claim for creation of lots of neutrinos. I can’t seem to find much on annihiliation online beyond the simple low energy high school physics where everything turns into photons, and the mention that in high energy annihilation lots of different particles can be created.

You make it in accelerators or I suppose magical aliens harvest it from cosmic high energy particle collisions. The book makes CERN out to be some sort of Illuminati led super secret base with Mach5 jet planes and other fancy things instead of cube offices and computer screens.

This is the post, but it references proton/antiproton interactions (ie from antihydrogen). Electron/positron reactions just produce gamma rays. And the problem is that the gamma rays interact weakly in air, so the dumping of energy is less central. I have no doubt that it would still go boom, though. But with a slow release matter/antimatter weapon, you could irradiate a large area with enough radiation to kill all life, but not do much physical damage to buildings, etc. A better neutron bomb, if you will.

Si

Help me out here. Shouldn’t all the antimatter get converted despite dispersal?

This is antimatter. It is the most reactive thing imaginable. On earth, even in the atmosphere rather than the surface, there is matter everywhere. Antimatter does not become less volatile as it disperses like fissionable material.

Yes there is a lot of empty space between atoms, but are we really saying that a particle of antimatter is going to travel very far before running into some matter? That energy must be realized as heat in the very least (if not explosive force) in the region of the release.

It doesn’t say anything about the amount of energy “lost” to neutrinos though. Anyone got numbers?

The question is what region and how quickly. If the dispersal/compression is not efficient, then the initial reactions will create a local vacuum from radiation pressure so remaining material will have to travel some distance before reacting. This slows down the energy dump. For a 500keV gamma beam, the 50% attenuation in air is ~60m, so for a 2.2MeV gamma ray from a electron/positron reaction it will be much greater than that, maybe 200m or more. So the energy from the reaction is not dumped directly into a small localised space, but heats a massive sphere of air. If it does not do this quickly or fast enough, you may not get the earth-shattering kaboom you were expecting - just a bright light in the sky, a wave of heat, and a lethal-to-all-life shower of gamma rays.

Of course, do the same thing in water or earth and it is a different story.

Si

Si

Honestly, the only way to determine this is to test.

Anyone have a couple of billion to design a antihydrogen cooling trap and container?

They already have these. Pretty sure Fermilab near where I live has (or had) some antimatter on hand. Doubtless there are other places that have some too.

Unfortunately (or perhaps fortunately) they do not have very much. Considering (according to Wiki) antimatter costs about \$25 billion/gram (by far the most expensive stuff on Earth) don’t expect to see a lot done with it anytime soon.

OK, let’s say that we have protons reacting with antiprotons. The most likely reaction path is for the protons to go to three pions. You’ll have about a 1 in 3 chance of getting three neutral pions, and a 2 in 3 chance of getting a pi0, a pi+, and a pi-, so let’s start with three protons and three antiprotons, just to make the bookkeeping simpler. That gives us 9 pions total, 5 neutral and 4 charged. The neutral pions will each decay into a couple of photons, so at this stage we’ve got 5/9 of the energy released in photons, none in neutrinos yet, and 4/9 of the energy in things yet to decay.

Now, the most likely decay path for a charged pion is to a muon and a mu neutrino. The neutrino is much less massive than the muon or pion, so we can approximate that all of the resulting kinetic energy goes into the neutrino, so the neutrino’s energy is the difference in mass between the pion and the muon. Pions are about 25% more massive than muons, so that works out to about 25% of the energy from the charged pions being lost to neutrinos in this step. We’re now standing at 5/9 photons, 1/9 neutrinos, 1/3 muons/antimuons.

Now, at this point the muons and antimuons could annihilate together into two more photons, but they’re probably going to be moving apart at a decent clip, so it’s more likely that they’ll decay, too. The decay of a muon releases an electron and two neutrinos. Electrons and neutrinos are both much less massive than muons, so the energy will be split about evenly between all three. So now the total energy bookkeeping is at 5/9 photons, 1/3 neutrinos, 1/9 electron and positron.

And electrons are stable, so they won’t decay, and the electrons and positrons from the explosion probably won’t meet up again for the same reason the muons won’t, but the positrons will find ambient electrons soon enough, and the electrons produced in the explosion will blend in with the crowd, which will have basically the same effect as if the electrons and positrons from the explosion did annihilate with each other. Electrons and positrons annihilate purely to photons, so at the end of the day, about 2/3 of the initial energy ends up in photons, and about 1/3 in neutrinos.

Note that this was a best-case scenario, with nothing but protons. If you’ve also got neutrons and/or antineutrons in the mix, then you’ll have a lot more charged pions in the initial pion mix, meaning a relatively larger proportion of neutrinos in the final products. This is probably where the 60% figure in the Wikipedia article comes from.