How would one be able to tell an antimatter explosion from a run of the mill normal nuclear detonation?

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Questa volta abbiamo cercato una curiosità scientifica:

Suppose someone figures out how to make 3 grams of antimatter leaves it to explode. How would it differ from a normal nuclear bomb? What kind of radiation and how much of it would it release? How would we able to tell it came from an antimatter reaction?

Ed ecco le risposte degli esperti:

That’s about a 129 kiloton yield, or ~532 TJ, if reacted with the equivalent mass of normal matter (equaling roughly 6 “Fat Man”-style nuclear weapons at once). If memory serves, antimatter explosions release more energy in the hard gamma ray spectrum than thermonuclear weapons, as they’re basically a “pure energy” weapon. Although realistically there will always be reactants that get blown away too fast to fuel the explosion in either case, the benefit of antimatter is that it will react with anything. We’d be able to tell the difference by residual radiation after the explosion; modern nukes use fissionable material that will spread over the detonation zone (ironically, the higher the yield, the ‘cleaner’ the explosion in terms of radioactive material residuals). Antimatter weapons will produce more initial ionizing radiation and secondary radioactive byproducts post-explosion, and overall they’re far more powerful.

The actual explosion would be quite similar from a distance. There be a lot more gamma rays that may be detectable from a distance if you are looking for them. However, you’d be able to tell quite easily from the aftermath as it would be a much “cleaner” explosion.

With fission, you’re splitting heavy nuclei like uranium or plutonium. Assuming it even all splits, there’s going to be some uranium and plutonium simply blown away. You have the daughter nuclei still left over from the split. The daughter atoms are all also unstable, they are far too neutron rich. As you move up the periodic table, you need more and more neutrons for an atom to be stable. Hydrogen takes none. Light ones like helium or carbon take an equal number of protons to neutrons. By the time you get to uranium 235, you need 143 neutrons to 92 protons to simply get an unstable nucleus with a long lived half-life. Splitting uranium means you still have a lot of neutrons, far more than the daughter elements are stable with. In addition, some lone neutrons fly off. These can hit other uranium atoms and cause them to undergo fission (hence the chain reaction), but they can also strike other atoms such as the bomb casing making them into radioactive unstable elements.

So you now have a lot of new radioactive elements. Some decay almost immediately, but their decay products are also usually radioactive. The chain can go on for some time until it hits a stable isotope. Most are rare, because they are radioactive with relatively short half-lives. These are isotopes you don’t see naturally like Strontium 90 or hydrogen 3 (aka tritium). Or even elements you don’t see naturally like Technetium. A bunch of very obvious signs the explosion was a fission explosion.

Fusion is different, in this case you are combining light elements to make heavier ones. We don’t fuse hydrogen like the sun though, that’s far to hard and slow of process. We fuse deuterium and tritium (hydrogen 2/3). The resulting product is stable helium, but it emits spare neutron radiation. Which as mentioned previously, can strike other heavier atoms and make them unstable. As well, every fusion weapon (also known as thermonuclear or hydrogen bomb) is also a fission weapon as well. Fission drives the fusion reaction, and then the neutron radiation from the fusion drives more fission.

Anti-hydrogen (or any higher element) annihilation makes neutrinos and gamma rays, eventually. Some exotic matter will be made first like muons (heavy electrons) or pions (things made of quarks that’s aren’t proton or neutrons), but extremely short lived. Even if not short lived, like say the positrons themsleves initially there of from the annihilation of the quarks, if it’s blow away it will react with the first regular matter it hits so it’s not getting far. Neutrinos fly through the earth and off into space with almost no interaction. Gamma rays will cause the immense pressure and temperature of the explosion. The gamma rays and explosion may be so powerful it would cause some radioactive products to be formed. However, the amount would be much lower than the fissible material and neutron radiation from a nuclear weapon. It also wouldn’t be the telltale products expected from uranium and plutonium, but other radioactive isotopes.

Tl;dr: Nuclear weapons, be they fusion or fission, make radioactive fallout. You’ll notice that. Theoretical antimatter weapons would not. You’ll notice the lack of expected fallout.

That’s not to say anitmatter bombs would be some improvement on nuclear weapons. Still outrageously dangerous. Plus, they’re fail horribly wrong rather than fail safe like nuclear. It’s hard to make a nuclear bomb go boom. It’s even harder to make sure anitmatter does not go boom.

A pure fission bomb has a characteristic distribution of fission products that reveals information on what the fissionable isotope was and how pure it was. Many people are familiar with the double camel hump plots that show these distributions. Gets a bit more complicated with fusion-boosted weapons. The double hump distribution of fission products is still there but it is affected by all of the fast neutrons from the fusion booster.

Both of these would be very different from what you would get with an anti-matter bomb. The simplest anti-matter bomb would use electrons and positrons. In this all of mass of both particles would be converted to energy in the form of two 0.512 MeV gamma rays at an angle of 180° (with small differences depending on the momentum of each particle) or three gamma photons with energies that depend on the angle between them but that add up two 1.02 MeV.

I am not really familiar with proton annihilation. Apparently not all the mass would get converted to energy as not all the quarks that compose the particle are annihilated. I really don’t know what this might produce but who can count on the fact that it would look nothing like any combination of fission/fusion bombs or even an electron/positron bomb.

The antimatter bomb would have much less radioactive fall out overall and all of it would be the kind produced by gamma ray irradiation. At least that’s the guess, no one has ever detonated an antimatter bomb to find out.

Antimatter makes gamma rays and neutrinos mostly. This will result in some of the stuff around the explosion becoming radioactive but most induced radiation is pretty short lived and not as much of it will be in the air.

A nuclear weapon makes neutrons and gamma rays along with being radioactive itself. Something like around 1% of the bomb material is converted to energy the rest is just pushed into the air for everyone to enjoy breathing for the next few decades. There will also be radioactive material produced by neutron bombardment which tends to be a bit longer lived then radioactive material produced by gamma rays because gamma rays just smash a nucleus apart whereas neutrons can be absorbed to change the nucleus a lot more.

If you just have basic equipment you will mostly notice the antimatter explosion has much less ionizing radiation, where as with more advanced equipment you will see that whole families of radioactives that are expected in a nuclear explosion are missing. The real big hint it was antimatter would be the lack of Plutonium-238 or Uranium-235 in the air because one or the other is needed for a modern nuclear weapon.