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Electron collision with nucleus

  1. Sep 7, 2012 #1
    I am abilogist who recently have to describe medical imaging....In this while explaining Bremsstahlung radiation, I am faced with a question. When a charged partcile like electron approaches another charged particle like nuclues in this case, does it undergo acceleartion or deceleration? since it experiences an attraction from nucleus, why does it slows down and not gains velocity? and what is the reason behind this phenomenon?
     
  2. jcsd
  3. Sep 7, 2012 #2

    mfb

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    The term acceleration usually just means "change in the motion" - it does not necessarily means an increase (or even change) in the absolute velocity.

    Electrons approaching a nucleus are attracted and gain velocity. But this is not the interesting part - they lose the energy again when they fly away. So the naive expectation would be that they do not gain/lose any energy. But accelerated charges radiate (and the direction of acceleration does not matter, it can even slow them down) - and this causes an energy loss.
     
  4. Oct 22, 2012 #3
    Hii Thank you very much for the insightful comments and explanation.
     
  5. Oct 23, 2012 #4
    Hmmm...

    Bremsstrahlung is 'braking' radiation. It doesn't specifically imply collision with a nucleus. In fact, such an event is extremely unlikely. Most of the energy loss of the electrons is due to interactions with the electron population of the target. Large numbers of secondary electrons are created which go on to further collisions and there are many energy loss processes involved. That's why the spectrum of Bremsstrahlung is very broad.

    You also get 'characteristic' X-ray spikes in the spectrum due to definite energy loss processes such as excitation of electron orbitals. But those are usually weak unless the target is a light element
     
  6. Oct 23, 2012 #5
    that depends on how you define collision. In many usages of the term, scattering is collision.
     
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