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Where do the electrons go? In alpha decay do 2 electrons follow the alpha particle and make stable Helium or does the larger daughter nucleus become an anion?

Also what do the electrons do in the mixture of fission and alpha decay? With Beryllium-8 it decays into two alpha particles and 4 lonely electrons or do you get two Helium atoms?If someone could add an entry to Holocron it would be greatly appreciated, thanks.

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2 Answers 2

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The electrons freed from the bounds of the fissioned nucleus will follow conservation of momentum and will move according to the kinetic energy they have. What will happen to them will depend on the medium they are in. Their kinetic energy will be too high for them to meet up with the fragments constructively, so there is very low probability the new nuclei will tie up with the freed electrons. The nuclei will pick up electrons from the medium, or remain ions.

Generally the electrons will lose energy by scattering on the fields of the atoms and molecules of the medium until they are captured. If in a neutral gas they may be captured by an atom/molecule and turn it into a negatively charged ion. If in solid , metal particularly they will end up in the conduction band.

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  • $\begingroup$ Do you have a reference for the idea that electrons are necessarily freed in alpha decay? What is the mechanism for that? $\endgroup$
    – Warren Dew
    Commented Nov 28, 2016 at 15:45
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    $\begingroup$ @WarrenDew I think it is self evident that a negative ion with two electrons in transient energy levels will not be stable. It will depend on the specific atoms and whether in a solid or liquid or gas, but negaitive ions lose their electrons. In bulk matter the alpha will pick up two electrons where it comes at rest, and the two freed from the decay will neutralize with some lifetime the whole system. $\endgroup$
    – anna v
    Commented Nov 28, 2016 at 18:28
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The alpha particles are emitted as bare nuclei, with charge +2. This is how alphas were originally distinguished from betas and gammas back when radioactivity was being discovered: the three species bent in different directions in a magnetic field.

It's possible to distinguish between a two-body decay (to alpha and negative ion) from a three- or four-body decay (to alpha, daughter atom, and electron) by looking at the energy of the alpha particle. In a three-body decay, like beta decay, the angles between the different particles aren't fixed, and so the beta particles are emitted with a broad range of energies. In a two-body decay, the alpha and the nucleus are emitted back-to-back, and the alpha always has the same energy.

There is some small probability for an electron to be knocked out during alpha decay, most likely from the innermost shell. In that case the alpha decay would be accompanied by X-rays as the electron cloud reconfigures itself.

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  • $\begingroup$ Thanks for the bit on what occurs if the alpha particle hits an electron. Nice tidbit! $\endgroup$ Commented May 19, 2015 at 4:03

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