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So, in this video (27:29) the guys says that "Mesons are short-lived particles that are more mundane and could pass through armour".

However, I don't really know much how particles work, in brand terms, how one could store these particles and shot them? They require to be "generated" in the moment of the shot? If so, how much energy I would need to generate Meson particles?

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    $\begingroup$ When you say "rifle" do you mean a portable longarm? Or are you thinking that the "spin" (in any sense of the word) matters? In the hard(ish) sci fi Traveller roleplaying game, meson guns are starship weaponry, not man portable. $\endgroup$
    – KerrAvon2055
    Commented May 20, 2021 at 23:09
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    $\begingroup$ The video sounds like it inherited the concept from the Traveller RPG''s Meson Guns , which don't act like real mesons, treating the half-life of the particles like a scheduled decay event instead of a probabilistic decay function. $\endgroup$
    – notovny
    Commented May 20, 2021 at 23:21
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    $\begingroup$ Yes you can store the mesons. Sure they decay a bit quickly (halflife of under 30 nanoseconds), but that's long enough, isn't it? $\endgroup$
    – PcMan
    Commented May 21, 2021 at 18:49

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It looks like you can create light mesons like pions (I'm assuming they're pions) with x-rays (produced by electrons fired at a platinum target) hitting a carbon meson source for 335 MeV (2.146917582e-11 Joules) per.

A typical gunshot has a muzzle energy of 500 Joules to 1,000 Joules. Assuming the process above scales linearly and can be miniaturized, you'd get a beam of 50 trillion to 100 trillion mesons for the same amount 500 -to- 1,000 Joules.

Pions can be charged for the sake of accelerating them towards a target, and have a lifetime of $1 \times 10^{-8}$ seconds. At such time, they decay into a charged muon and an uncharged muon neutrino. Even at the speed of light, this would only have a range of about one meter (3 feet).

But what you are probably looking for is kaons, which I can't find a source for, but have a mass about 4 times that of a pion (so maybe you get 250 trillion for a rifle shot). Kaons decay into neutral pions (which are probably the armor penetrating particle you are looking for) in $1 \times 10^{-8}$ seconds. Kaons are charged, so you could accelerate them up. But, like pions, even at the speed of light, these only have a range of about 1 meter (3 feet) until the kaons decay, plus about another meter (3 feet; 6 feet total) as pions. These neutral pions decay into photons, so all of this energy is absorbed by the target as heat.

Per this source (https://melindajolleyacademia.weebly.com/uploads/2/1/3/3/21333742/muon_lifetime_and_time_dilation_effect.pptx) time dilation could arbitrarily extend the lifetime (and range) of these particles as you near the speed of light.

To get a typical rifle range of around 200 meters, then, you’ll need to accelerate this mass to 0.995 c (0.99 c if you're using kaons). Per here (https://www.vcalc.com/equation/?uuid=85b315c3-baf3-11e3-9cd9-bc764e2038f2) this will cost you about 200 times the rest energy of the beam you created (200 times 1,000 joules or 200,000 joules)

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    $\begingroup$ Muzzle energy is meaningless since bullets do kinetic damage and mesons don't; they do radiation and (indirectly) thermal damage. A pulse of mesons with 1 kJ of energy may do enough radiation poisoning to kill a person in a few hours but, in terms of thermal energy, it's only enough to warm a cup of water about 4 degrees Celsius. And you probably won't even get that much; actual energy transferred from the meson pulse depends on the radiation cross section of the target; most of that pulse may pass right through it. $\endgroup$
    – GrumpyYoungMan
    Commented May 20, 2021 at 23:12
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    $\begingroup$ Given that the mesons are described as readily passing through armour, it suggests that the radiation cross-section w/r to mesons is not substantial at all. $\endgroup$
    – jdunlop
    Commented May 21, 2021 at 0:28
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    $\begingroup$ I may be wrong, but I’d think the whole 200kJ of accelerated energy would be deposited into the target. Agree that this weapon has a minimum and maximum effective range. Might be possible for a firing computer to control the beam speed, so that the target is in the best spot. $\endgroup$
    – James McLellan
    Commented May 21, 2021 at 1:01
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    $\begingroup$ I'm thinking the efficiency of such a weapon would be very low. Probably more than 100 Joules in to get 1 Joule out. So you'd need to generate about 20 Million Joules to get 200 K joules of beam. Since a typical bullet has about 1K of energy, you'd need 20,000 bullets worth of energy. I don't see this being person-portable. $\endgroup$
    – puppetsock
    Commented May 21, 2021 at 17:55

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