Suppose in the future we are hit with an explosion of unknown nature.
A fission weapon, IIRC, has certain isotopes of cesium and strontium in the fallout.
Fusion weapons have lithium isotopes in the fallout.
What, if any, telltale components can be found in the residue of a M/AM detonation?
This has already happened. The Tunguska explosion of June 1908 was of unknown origin. Three different groups suggested independently that it was due to an explosion of an antimatter object entering our atmosphere.
The first was Lincoln la Paz, who had translated Leonid Kulik’s expedition reports to the site into English for the magazine “Amateir Astronomy”. He suggested that the explosion was due to “contraterrene” or “Dirac-style” matter 9the term “antimatter” hadn’t been popularized yet), since there was evidently no debris at the site. Later on, in the late 1950s the idea was proposed by other groups.
I’m not sure what the products would be that you could find. The antimatter itself could be, one supposes, of any weight, but would be completely consumed. The products are a lot of high-energy photons (gamma rays) and a lot of relatively simple matter created by particle-antiparticle generation in the burst. I don’t think there’s anything “signature” about it, unless you consider the lack of significant heavy matter itself a signature.
The same sort of question arises in astronomy. More generally, how can astronomers tell whether a given star, say, is made of matter or antimatter? If a star in our galaxy were made of antimatter, then we would expect its stellar wind to also contain antimatter, and so should annihilate when it reaches the matter in interstellar space. Astronomers look for 511keV gamma rays, which are a signature of cold positron-electron annihilation (511keV/c[sup]2[/sup] is the rest mass of the electron); when they don’t see them they deduce that the star is probably not an anti-star. This sort of transitive comparison works as long as there is a sufficient density of matter in the region between the objects for observation of the gamma radiation that would result from annihilation.
So if the “antimatter bomb” is made from normal, cold, stable antimatter (say, a block of antiantimony–would that just be “mony”?), the electron-positron annihilation should produce a fairly sharp 511keV peak (though I’m not sure if photons count as “residue” for your purposes). The baryon-antibaryon annihilations are much more complicated, since baryons are complicated composite objects, but they probably still have a recognizable signature with lots of ~100MeV photons.
I’m pretty sure Tunguska was deemed to be an impact event…
::checking Wikipedia:::
Here we go. Wiki says it was "most like caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometers (3–6 miles) above Earth’s surface. "
The article also says this about the antimatter hypothesis:
ETA: I tried to post this an hour ago, but the hamsters ate it.
I’m pretty sure it was an impact event, too. I didn’t say I believed it was antimatter.
Kulik said that he found physical remnants, too (although virtually nobody’s writings on the topic seem to know this, aside from Krinov, who was there), so la Lap (who suggested this in the 1940s or early 50s) shoulda known better. The objections to it being antimatter were pretty obvious to me when I first wrote about this in college, and I imagine they were pretty well known to others, as well. But the Tunguska event has pretty much been a cosmic Rorschach Test, with everyone seeing their favorite non-mundane effect — cosmic dust clouds, cometary nuclei, anti-matter, exploding alien spacecraft, quantum black holes, or what have you – embodied by it.
As Omphaloskeptic indicates, there are a few signatures you could look for during the explosion. In addition to the electron-positron annihilation products (511 keV photons), the proton/antiproton and neutron/antineutron annihilations will lead to a spray of pions and kaons and muons. The muons would get the farthest from the explosion, so you could look for those. (“Conventional” nuclear weapons won’t produce any muons.)
However, you’re probably more interested in post-explosion evidence. If an antihydrogen blob hit the earth, you’d end up with some unexpected isotopes lying around (as the antiprotons will have partially eaten into the carbon, oxygen, etc., nuclei). If instead, the explosion was produced by a hypothetical controlled hydrogen-antihydrogen contraption, perhaps with more hydrogen than antihydrogen to ensure complete burning of the antihydrogen, then you would have not much out of the ordinary left behind. Perhaps the hypothetical technology needed to transport the antimatter could be identified. Also, the secondary particles produced in the explosion could radioactivate nearby materials, but I’m guessing this would be a small effect (though I haven’t run the numbers).
Heh, good one.
Some numbers:
It only takes 0.02 grams of completely burned antimatter to make a 1-megaton-TNT-equivalent explosion. Assuming:
With these numbers, I find that modified nuclei will exist at the 0.1 ppb level in the nearby material. (Of course, this is the same material that just got blasted all over the place.) So while it would depend on the exact background levels of the long-lived isotopes, my guess is that this residue would be impossible to find, leaving only the antimatter-directly-attacks-earth-material residue to search for, which has the advantage of being localized to the contact point, but still faces the blown-to-smithereens problem.