Do Alpha Particles attract electrons? I would think they do because an alpha particle is just neutrons and protons bonded tightly, so they should want to be neutral, so they should attract electrons, but every place I've looked says they don't and I don't understand why.

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    $\begingroup$ What places do say that they do not attract electrons? $\endgroup$
    – nasu
    Nov 1, 2019 at 16:59
  • $\begingroup$ Maybe it's because once it has electrons it's no longer an alpha particle, it's hard to say what your other sources mean without context $\endgroup$
    – Triatticus
    Nov 1, 2019 at 17:00
  • $\begingroup$ Would you mind citing those sources that say that? Alpha particles for sure have a net positive charge, and very willingly interact with matter. en.wikipedia.org/wiki/Alpha_particle $\endgroup$
    – Steeven
    Nov 1, 2019 at 17:01
  • $\begingroup$ Indeed, helium would much prefer to be neutral. But sending it off at high speed, and through things, tends to strip the electrons off of it until it slows down considerably. $\endgroup$
    – Jon Custer
    Nov 1, 2019 at 17:01

1 Answer 1


Alpha particles are Helium-4 nuclei which means they have an overall electric charge that is double the opposite charge of an electron. They indeed get attracted to electrons by simple Coulomb force

$F = -2kq^2_e/r^2$

, where $r$ is the distance between the alpha particle and the electron, $q_e$ is the elementary charge and $k$ is Coulomb's constant.

The fact that alpha particles can form Helium atoms depends on the conditions. You need free electrons around so the nucleus is able to capture them (something your alpha particle will not always find in the interstellar medium) and you relative velocity between both to be small; a stream of relativistic alpha particles traversing an electron flock will have little time to make the electromagnetic interation operate enought for a capture, and the energy of the encounter will be larger than the one needed to mantain the electron bounded to the helium nucleus. You also don't want any scenario where capture is somethign ephimeral since the captured electron could be in an excited state and jump quickly from there to become a free electron again. Photons may also excite helium atoms to the point where any captured electron can't mantain its energy level and the atom becomes fully ionized again.

So yeah, they should create Helium atoms in many scenarios but you always need free electrons around and not so highly energetic interactions going on.

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    $\begingroup$ Indeed, and the way alpha particles were proven to be helium nuclei was to capture a bunch in a sealed glass bottle and measure the spectrum of the resulting gas, showing it was the same as helium. It really isn't too hard to find spare electrons to attach once the nuclei has slowed down enough. $\endgroup$
    – Jon Custer
    Nov 1, 2019 at 17:20

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