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Advantages of Electron Scattering over Alpha-Particle Scattering?

  1. Jan 27, 2012 #1
    Hi Guys,

    I'm doing a practice exam paper and I stumbled upon a question I can't answer for 5 marks.

    Describe the advantages of electron scattering over alpha particle scattering. Sketch a graph of charge density vs distance from centre of nucleus. From the graph, explain why protons are more influenced by strong force than coulomb force.

    I've been looking around the net and can't seem to find a direct comparison between electron and alpha scattering. I understand that high energy electrons can penetrate the nucleus, I understand that alpa scattering gives closest approach... but where's the real advantage?

    Can't seem to find charge density vs distance either

    I understand that strong force works at 1fm, disappears at 2.5fm. What range was protons at again? Can't seem to find it.

    Help me out please! Exam in few days!

    Thanks in advance
     
  2. jcsd
  3. Jan 28, 2012 #2

    BruceW

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    Homework Helper

    hmm. The first question is what are they using the scattering for? To probe the nucleus? In this case, I guess that 'charge density vs distance from centre of nucleus' is talking about the density of the nucleons inside the nucleus.

    Have you taken lecture notes about this kind of thing? Looks like a difficult question. Both electrons and alpha particles have been used to probe the nucleus, so obviously there are advantages to both. Maybe just start with writing down the differences, and then make some reasonable arguments for advantages.

    Or maybe the question is talking about probing the atom? This is more likely, since it is the easier / more basic physics. What have you got in your lecture notes?
     
  4. Jan 28, 2012 #3
    Yeah if I actually turned up to half my lectures I wouldn't be here unfortunately....

    Yes, sorry I meant for probing the nucleus. The differences that I can so far comprehend is that alpha particles will not over come coulomb forces, so it will deflect at a solid angle. Where as high energy electrons will penetrate the nucleus because it gains magnetic momentum and the experiment takes recoil into account. That means you will get a more precise measurement of the radius of the nuclei...but is that all I need for 5 marks??? (and the graph)

    I found out that nucleons are usually around 1.3fm. And the strong force is good from 0.5 to 2.5fm so that's why protons are influenced by strong and not EM.

    Still can't find the graph though
     
  5. Jan 28, 2012 #4

    Astronuc

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    Staff: Mentor

  6. Jan 28, 2012 #5
    I'm going to lay down my thoughts to your response.

    Differences: Electron vs Alpha

    Size and mass: Small - Big
    Charge: Negative - Positive
    Energy obtainable: Higher energies - lower energy
    Frequency: Higher frequencies - lower frequencies
    Wavelength: shorter - longer

    These factors make the electrons more penetrable without "bumping into objects".
    From rutherford experiments, the nucleus has a positive charge provided by protons.
    Shooting a high energy electrons at nucleus will have an "attracting" effect?
    Provided electrons do not "bump" into nucleons. The electrons will be repelled by strong force at 0.5fm?
    This gives an accurate measurement of the size of nucleus?

    Guessing charge density is 1/r^2 relationship?

    Please comment and correct
     
  7. Jan 28, 2012 #6
    I would say that the big advantage of electron beams is that they can be easily produced and the energy can be easily varied by changing accelerator voltage.
    With alpha particles you are limited to the energies available from radioactive sources.
    I have not heard about alpha particles being accelerated but I know that beams of protons are sometimes used because they can be produced and accelerated....just like electrons.
     
  8. Jan 28, 2012 #7
    AHA!!! You just gave me the last puzzle piece!

    The advantages would be the following (I think):

    1) Electrons will only interact by electromagnetic force (Not strong nuclear like alpha will)

    2) High energy electrons will have a very short wave length so the nucleus will be "resolved"

    3) Electrons can be energy filtered (thanks for the clue) unlike alpha so only elastically scattered electrons can be detected.

    Now all I need is that graph...
     
  9. Jan 29, 2012 #8
    Found the graph:

    4703501.jpg

    Thanks for the help.
     
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