I am envisioning a weapon that operates similarly to a proton therapy machine, only with the aim of killing a person. Essentially, a beam of protons is launched towards the target. However, the proton dumps most of its energy over a narrow range. In real life, this is used in cancer therapy to irradiate a tumor while minimizing damage to surrounding tissues. The purpose of such a weapon is to be able to kill a target that is behind cover (Such as a wall) and/or equipped with armor that is capable of protecting against bullets. Essentially, a beam of protons is created that moves just fast enough that it could pass through a wall, but loses enough energy in the process that, once it encounters something dense (Like a human body), it will dump most of its remaining energy into that something. The cause of death from being shot at by such a weapon would be either thermal injury or radiation poisoning.

Combat is expected to take place in atmosphere and in space. However, I do not know just how much energy would be required to generate a beam powerful enough for this purpose, whether it is possible to generate said beam within a reasonably-sized structure, whether such a beam would be able to travel long distances, and whether such an application is actually possible.

Is such a weapon, either handheld or mounted on a vehicle, feasible?

In other words: Can this phenomenon be weaponized?

  • $\begingroup$ At its most basic you can use Relativistic kinetic energy equations to estimate the energy of a Proton at a given velocity. However, the truth of the matter is that such a weapon wont really do much. The LHC shoots millions of Protons a second and is several km across. And even then it probably wouldnt kill you. $\endgroup$
    – ErikHall
    Commented Feb 2, 2023 at 16:50
  • 2
    $\begingroup$ There is a lot on this stack about particle beams. Loads of leisure reading. You could start with worldbuilding.stackexchange.com/questions/183242/… $\endgroup$
    – Willk
    Commented Feb 2, 2023 at 18:08
  • $\begingroup$ @ErikHall Anatoli Bugorski would agree with you to some extent but I would not want to try it given his experience. $\endgroup$
    – JonSG
    Commented Feb 2, 2023 at 20:05
  • $\begingroup$ The LHC is maybe not a good guide to a beam weapon. They are interested in getting particles to the highest possible energy in the narrowest possible beam. A beam weapon would be more interested in total energy in the beam with much laxer requirements on confining the beam. $\endgroup$
    – Boba Fit
    Commented Feb 2, 2023 at 20:41
  • 1
    $\begingroup$ @JonSG , me neither. While the protons probably wont like kill you instantly the Gamma Radiation might in a month or so. I mean heck, there is a reason why the detector of the LHC is behind like a lightyear of protection. $\endgroup$
    – ErikHall
    Commented Feb 4, 2023 at 19:20

1 Answer 1


Radon ions!

In just a few lines I am going to recycle my old answer which also considers particle beams as used for cancer treatment. In short: I pick radon for the particle because they are big atoms that pack a wallop and have a energy deposition point which is predictable. Neutral radon atoms would not be reactive along the way which could be good although with current tech it is hard to accelerate neutral atoms. Charged ions can be accelerated electromagnetically; I have to think radon would still be less reactive than most, it being a noble gas.

Recycled answer from the halcyon days of 2020:

What subatomic particle is best for a particle accelerator gun?

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.

Last: short fiction featuring particle beam and Bragg point!


  • $\begingroup$ Radon has the additional benefit of radioactively contaminating the spaceship it hits even if it's a non-killing blow $\endgroup$ Commented Feb 5, 2023 at 0:48
  • $\begingroup$ @ChristopherHostage - also it decays into lead, so you will get lead poisoning from the radon atoms that plowed into you. Triple threat! $\endgroup$
    – Willk
    Commented Feb 5, 2023 at 3:59

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