Shooting an electron at an ion's nucleus

1. Aug 16, 2011

jkjkjk

I am just a tiny bit confused at what would happen if you shot an electron directly at an ion's (with no electrons like deutrium 2+....) nucleus? would it stop and if so why?

2. Aug 16, 2011

DrChinese

Welcome to PhysicsForums, jkjkjk!

You would see scattering between the electron and the nucleus. But there would not be "direct" contact in the sense that the electron "hits" the nucleus.

3. Aug 16, 2011

xts

1. What do you mean by 'directly'?
2. The asnwer depend on energy (in centre of mass) of the shot.
For low energies the electron would just got scattered (deflected) and some radiation (mostly X and gamma-rays) will be generated. For bigger energies the whole zoo of particles and antiparticles will be created. There are large laboratories utilizing such collisions (e.g. HERA - Hadron-Electron Ring Accelerator at DESY, Hamburg, colliding electrons with protons, but also, in limited range, with deuterons and even heavy ions)

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4. Aug 16, 2011

jkjkjk

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That is what I don't really understand why wouldn't there be direct contact.

5. Aug 16, 2011

jkjkjk

1) Yer sorry i was just meaning shooting an electron so it hits the nucleus sort of at the centre of a face (I realise it wouldn't be that accurate)

2) Yer I get you point but I was just trying to get at what would stop it

6. Aug 16, 2011

xts

Well - what does it mean 'direct contact'?

Actually in most such cases electron passes through the nucleus (through the proton), and is just deflected (with some Bremsstrahlung radiation).
There is nothing which could stop it. (Except of very-very-very low chance of being absorbed by proton, and convert it to neutron, but - honestly - I don't know if such reaction got ever observed, and don't ask me to calculate its weak probability)

If it has high energy it may kick out one of the quarks of the nucleus - and that quark, leaving the proton, creates pairs of quark/antiquark, then you see the whole explosion of various mesons spreading out, and the proton gets converted to some possibly strange, or even heavier baryon.

If your electron has very low energy, and it is shot at an ion, it may be just captured by it to form back an atom - emitting photon to balance the energy.

And, one more reaction (seen quite often if available energy is sufficient): electron, passing by nucleus, may create a pair of electron/positron, muon/anti-muon, tau/anti-tau.

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7. Aug 16, 2011

jkjkjk

I didn't realise that it could pass through the nucleus

thanks

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8. Aug 16, 2011

DrChinese

Quantum particles - such as an electron - do not have a size in the classical sense of the word. Electrons behave much as point particles, in fact, meaning they occupy no volume. However, electrons are charged, and this creates interactions with other charged particles. Despite what you might expect, a negatively charged electron is not so attracted to a positively charge nucleus that they will "touch". At a certain point, they don't want to get any closer. This is a gross oversimplification, but that is the essential answer.

9. Aug 16, 2011

xts

Yes, they can. Actually, scattering electrons is a good way to analyse internal structure of the nucleus (the same way as 100 years ago lord Rutherford analysed the structure of atom: http://en.wikipedia.org/wiki/Rutherford_scattering). Using higher and higher energies of electrons you may discover smaller and smaller details. First you may find, that nucleus is not a point, but it occupies some space - it may be seen as an uniformly charged sphere of the diameter $\sqrt[3]{A}\cdot 2.5\cdot 10^{-15} {\rm m}$
As you start to check if the charge is really uniformly distributed there, shooting it with higher energy electrons, you may discover it is combined of mixture of charged protons and non-charged neutrons, looking like balls of diameter $1.75\cdot 10^{-15} {\rm m}$ As you go deeper - you may find that nucleons also have internal structure: in each of them you may find 3 charged quarks. In all experiments, and also theory says so, the quarks may be considered (like electron) as charged points.

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10. Aug 17, 2011

jkjkjk

Yer that is probably where my thinking is hugely wrong, that I can't stop thinking that an electron is not a billiard ball like object.

What I would really like to know is what forces (if any) would stop it when it gets close?

Last edited: Aug 17, 2011
11. Aug 17, 2011

jkjkjk

I have just realise that this sort of thread has been done to death and I am sorry about that

12. Aug 17, 2011

DrChinese

No problemo! I would encourage you to read up some more and come back with more questions. It is a fascinating world we live in!!

ZapperZ posted a nice FAQ here which addresses the area covered in this thread in a little more detail, check it out: