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Theoretically, assuming it was possible and practical to take a particle accelerator and turn it into a gun/cannon weapon, and use it to shoot accelerated subatomic particles. What sort of subatomic projectile would cause the most damage?

Assuming for a moment that the technology in question is powerful enough to break the strong and weak nuclear force (and not just turn the weapon into a straight up bomb), what would make the biggest bang for your buck. protons, neutrons or some other particle? As in, what would affect the atoms of your target and create the greatest detonation?

Another point of my question isn't what subatomic particle is the best bullet, but rather what subatomic particle when shot at a target can better destabilise the targets atomical structure, kind of like the "Little doctor weapon from the movie and book Ender's game" that shoots a sort of energy beam at a planets ring system and disintegrates it on a molecular level.

And finally, how would it work (from a theoretical standpoint, what would it do).

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    $\begingroup$ A weapon like this would not work in the atmosphere as it is just going to ionize the air and have no range. Also particles that can penetrate air can't be accelerated by a particle accelerator. Also for the affect of hitting stuff in space with a weapon like this, it doesn't matter which particle you use as the main thing is the energy you deliver is going to be what does the damage and any particle that can practically be accelerated will do. $\endgroup$ – A. C. A. C. Jan 5 '18 at 19:55
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    $\begingroup$ Every particle in the beam will do damage to every atom in the air and in the target it strikes. But I suspect that "destabilise the targets atomical structure" is not correct. Particles in the beam may destabilize the individual atoms in the target that they hit, and the individual molecules those atoms are part of, but they aren't going to destabilise any parts of the target they don't hit. A beam one inch in diameter may drill a one inch wide hole through someone, but it won't make his entire body vanish, despite what some movies and TV shows depict. $\endgroup$ – M. A. Golding Jan 5 '18 at 19:55
  • $\begingroup$ The only correct answer here is "one that you made up". Seriously. That's what Card did for Ender's Game. Real particle beams just don't do what you want. $\endgroup$ – dmckee Jan 5 '18 at 22:14
  • $\begingroup$ @A.C.A.C. while it's range wouldn't be very good, there is some precedent for particle beams in air, some electron beam welders run in the open air. Although the insides of the electron gun itself are kept under vacuum, the beam itself moves through the air in some applications and then there's the unfortunate case of Anatoli Bugorski who got in the way of a proton beam while inside an accelerator that was happily ticking away at atmospheric pressure. $\endgroup$ – Samwise Jan 5 '18 at 22:43
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The ever useful Atomic Rockets has a section on Space Warfare "conventional weapons" which has most of the details you need to understand particle beam weapons (and almost every other type of weapon).

Short answer: ain't happening, hoss.....

Particle beam accelerators use the property of ionized particles to manipulate the particles, both to accelerate them, focus the beam and direct the beam. So long as the beam stays inside the accelerator, all is good, but open the port and let the beam escape, and the mutual repulsion of the particles will cause the beam to rapidly dissipate, as high energy electrons, protons or ions rapidly fly away from each other.

During the 1980's, as part of the Strategic Defence Initiative (SDI), two ideas surfaced which might allow the use of particle beams in space and in the atmosphere.

  1. Neutral Ion beams. This isn't some mind bending alteration of the laws of physics, but rather the ion beam from the accelerator was to pass through a cell of some neutral gas and strip electrons from the gas to neutralize the beam. The highly charged and fast moving (relativistic) beam would enter the cell, and emerge moving slightly slower but with the charge largely neutralized. This didn't solve all the problems, and the beam was calculated to sell spread out due to thermal blooming, but you could get a few thousand kilometres range. Of course with 80's technology and launch platforms, each neutral particle accelerator would take many flights to build, and be giant targets floating in orbit.

enter image description here

TRW concept for a particle beam weapon. Image via Scott Lowther

  1. Electron beams for ship defence. The US Navy considered the problem of shooting down incoming antiship missiles, and concluded that an electron beam would be a good weapon, being able to deliver lots of energy to the target, both thermal energy which might cause structural failure to the missile airframe, and the electrons themselves would damage any onboard electronics. Since the atmosphere would absorb the beam, and the mutual repulsion problem would make the beam useless at all but the shortest ranges, the concept was tweaked to have a high power laser fire first. The laser would create a partial vacuum along its path due to the energy being deposited in the air, and the electron beam would naturally follow the channel. The full physics escapes me (the fact the beam ran down a channel of partial vacuum allowed the beam to remain focused for a much greater distance than otherwise), and you might also reasonably ask why not just use the laser to shoot down the missile. As of 2018, the Navy has answered "you know, why not use the laser?" and prototype laser weapons are now being installed on ships.

Now there is one way to utilize a particle beam to make an effective weapon capable of being used both in the atmosphere and in space. Use a very high power electron beam to drive a Free Electron Laser (FEL). By varying the power output of the beam as it passes through the "wiggler" magnets, you can vary the wavelength of the laser beam which emerges from the optical train, going for very short wavelengths utilizing small mirrors or diffraction gratings for space, and stepping down to infrared or other frequencies which fire through "windows" where your atmosphere is transparent to the wavelengths for surface combat on a planet.

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Anti-matter

Anti-particles would get you the most bang, so to speak. They'd also react with the air. So, you could come up with some sort of containment to make them last longer, like a pulse of anti-electrons surrounded by a large number of protons, or just have an anti-matter flame thrower that spews them continuously. But you'd need a good shield since you'd be closer to the weapon than the target would be, and it wouldn't go very far.

Neutrons

The best travel, the best mass, and if the target is made of the right material you could trigger a fission or fusion reaction. But most things are not affected by neutrons and they would pass right through.

Protons or electrons

Instant plasma! Protons have more mass, and may follow a straighter path, but both will immediately interact with particles nearby. If you had a lot of them flowing in the same direction you'd ionize a path, creating a beam of plasma. Crazy high energy needed, and it might form a fractal pattern more than a straight line.

You might have some sort of laser that guides the plasma or pre-ionized the path of the particles to reduce the spread and energy loss, but it's pretty far from understood physics and would require a bunch of handwaving about the mechanics.

Alpha radiation

Using ionized helium nuclei would have more mass and a straighter path, and could have instant negative effects on DNA, similar to alpha radiation from plutonium. Alpha radiation is stopped by a sheet of paper or other similar minimal barrier, but if you had enough of it going fast enough, you could cut a path. This would probably be like a death ray, creating an ionized beam that is particularly destructive to organic material. Still very short ranged and very ionizing, but a reasonable fuel source would be a canister of helium gas.

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    $\begingroup$ "have an anti-matter flame thrower that spews them continuously" Well, that'd certainly kill anyone in the vicinity. It'd unfortunately also be exceptionally likely to kill the person wielding it, and might possibly obliterate itself (I'm not completely sure about that one), by gamma radiation from the matter-antimatter annihilation process if nothing else... $\endgroup$ – a CVn Jan 5 '18 at 20:26
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    $\begingroup$ But it would be a spectacular weapon to behold. $\endgroup$ – user15741 Jan 5 '18 at 20:29
  • $\begingroup$ I'm just imagining a plasma beam weapon with little fractals spiraling out from the beam. How amazing would that look... $\endgroup$ – Dent7777 Jan 5 '18 at 20:32
  • $\begingroup$ Neutrons aren't totally useless, they're good at making whatever they bump into radioactive by barging into the core of nearby atoms and destabilizing the nucleus, plus dense stuff makes for bad neutron shielding (opposite rules to x-rays, so your body armour does little to protect you from your crazed particle-beam-wielding assailant) $\endgroup$ – Samwise Jan 5 '18 at 21:01
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    $\begingroup$ Frankly you are ignoring the real experience that particle physicists have in handling actual particle beams (even positron and anti-proton beams). The interaction cross-section of particles is energy dependent, it drops rapidly moving from low to moderate energies, stays low for a wide stretch and then rises slowly with beam energy. This fact is vastly useful in radiation therapy, but it makes a hash of "and it'll go boom" ideas of what beam weapons can/will do. Also of great interest are space charge effects which blow up beam sizes very rapidly in the absence of active containment. $\endgroup$ – dmckee Jan 5 '18 at 22:13
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Answer: radon.

A particle beam weapon would be good for shooting something where you did not want to burn a hole in it, but rather wanted to deliver energy to something inside - perhaps a lifeform, or some element of a spaceship. The precision (in 3 dimensions) would minimize damage to the rest of the target which might be desirable for various reasons. It might be less likely to blow up. Or you could salvage it. Or you could disable a ship without punching a hole in the side and killing the crew.

As background consider what real particle beams are used for. Conventional radiotherapy uses photons which is electromagnetic radiation. Particle radiation has the benefit that a moving charged particle unloads its energy mostly at the point where it slows down.

from http://radcare.org/types-of-radiation-therapy/particle-beam-radiation-therapy

proton vs photon radiation

So a particle beam is good for depositing energy at a specified distance into an object, and that energy deposit site (here a tumor) can be governed by adjusting the amount of energy put on a proton.

Other ions are used for particle beam radiation. One hears about carbon ion radiation and I see that other particles (neon, krypton) have been tried.

from The Emerging Role of Carbon-Ion Radiotherapy

While conventional radiation generally passes continually through a biological target, with dose delivered roughly equivalently throughout the beam path, particle beams release energy at the inverse of their velocity. Particle beams thus deliver a lower entry dose, depositing the majority of their energy at the flight path terminus, yielding an asymptotic dose peak (the “Bragg Peak”) (15). This allows for a dose concentration distribution impossible with conventional irradiation methods.

Today, proton dominates particle therapy. However, the larger mass of carbon results in decreased beam scattering, yielding a sharper dose distribution border with minimal penumbra (16). Radiobiologically, carbon-ion beams result in two to three times the relative biological effect (RBE; the biological effectiveness of one type of ionized radiation relative to another, given the same amount of absorbed energy) of proton and conventional irradiation methods

So the more massive the particle, the more kinetic energy and the more precise the beam? Apparently not.

https://www.bnl.gov/nsrl/userguide/bragg-curves-and-peaks.php is an excellent reference on Bragg curves, which depict energy deposition at given depths for a charged particle with a given energy.

braggg curves

From that site

When the primary ion of high-Z breaks up, it results in several low-Z fragments, each of which deposits small amounts of energy in the material. The sum total of all the energy deposited by all fragments can never add up to the energy deposited by the primary ion. This causes the Bragg Curve for fragmenting high-Z ions like Iron to drop initially.

So heavy ions like titanium and iron and gold which fragment do not cleanly bring their energy to a given depth and drop it off - they fragment and deposit energy along the way sort of like electromagnetic radiation. Sloppy.

Carbon must not fragment like that and neither do xenon or krypton. I presume xenon and krypton do not because they are noble gases but why that should be true (or what governs the tendency to fragment in a given ion) is beyond my ken.

So: more massive = more punch, and noble gases are less fragment prone and more likely to deliver the energy at the depth you want. Radon is the heaviest noble gas and so that is my answer.


Addition in case you want to use this in an atmosphere and the air is in the way. 1: Shoot a dart with a conductive wire. 2: Turn the wire into plasma with a huge electrical charge. It will in essence be a horizontal lightning bolt. 3: The expanding plasma will leave a low density core of near vacuum. It will be where the wire was. 4: Discharge your particles down this transient vacuum path.

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