# Which particles can go right through the atom?

Can elementary particles (like the electron, photon, or neutrino ) go through an atom (not the nucleus)?

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Can you define "go through" here? – Kyle Kanos Apr 25 '14 at 12:43
Beta particles can..See Rutherford's gold foil experiment. – biogirl Apr 25 '14 at 12:46
"go through" - i mean, atom is vast and has tiny nucleus at the center. most of the charged particles cannot enter the electron sphere, but electrically neutral particles like neutrino can go inside the electron sphere and come out in a straight line (only if it hit the nucleus it is stopped). – user45246 Apr 25 '14 at 13:04
In general, depending on the specifics of the radiation, electrons, photons and neutrinos can all pass through atoms in certain circumstances. The absorptive and scattering cross-sections will often depend on the radiation energy and the properties of the atom, though. – DumpsterDoofus Apr 25 '14 at 14:37

Any sufficiently fast particle can go through the atom since the repulsing force is finite and you can prepare a projectile with a high enough energy.

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Most sub-atomic particles can.

In the Rutherford gold foil experiment, alpha particles (helium nuclei) often went through atoms. Beta particles (high speed electrons) can go through paper. There are more than a billion neutrinos going through you every single day.

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It depends on the probability of interaction. This probability is computed using Fermi's golden rule, and it involves the strength of the interaction and the number of allowed final states. Weaker interactions means higher probabilities of going through the atom. Some examples:

• Neutrinos only feel the weak interaction, so their probability of going through the atom is almost exactly one.
• Neutrons don't interact with the electronic shell, but do interact with the nucleus via the strong force (this is how fission reactors work).
• Photons can be absorbed or produce stimulated emission if they have the frequency of a spectral line. Energetic photons can also suffer photoelectric effect, Compton scattering, pair production, etc.
• Protons, electrons and $\alpha$ particles have electric charge, so they will interact electromagnetically with the atom. The probability of going through increases if the particle goes faster.

Notice that I've talked about probabilities. As far as I know (correct me if I'm wrong), there's no known particle that has a zero probability of interaction with electrons and/or nuclei. Sometimes they will go through, and sometimes not.

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