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Questions regarding Gamma EMR

  1. Jul 2, 2011 #1
    I am very uneducated in physics, however I did take a remote sensing course in college where we discussed EMR. My questions are the following: could gamma radiation be absorbed in a material and then transferred to another material or dispersed. I know that gamma radiation has no charge and is only slightly affected by magnetic fields. I know that a super dense material like lead is routinely used to absorb gamma radiation. If gamma radiation has properties of no mass or electrical charge yet are EMR then there has to be a way to match the frequency of this pre energy. Could a field of ionized radiation matching the frequency of gamma radiation deflect a jet of gamma radiation (deflect energy with energy). I may be way off on this so please bare with me.
     
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  3. Jul 3, 2011 #2

    Drakkith

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    Gamma radiation is plain old light but at a much much higher frequency and carries with it much greater momentum and energy. The only way to shield from it is to absorb it. This is accomplished with lead or other dense materials because dense materials occupy the least amount of space, which is always a sought after property since designing a reactor or something similar with 100 ft of Styrofoam is just silly. (Just using it as an absurd example.)

    Just like normal light you cannot shine two beams of light and deflect each other with them. EMR doesn't readily interact.
     
  4. Jul 3, 2011 #3

    mathman

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    The effectiveness of lead as a gamma ray shield is more than just the density. The absorption cross-section increases with atomic number.
     
  5. Jul 3, 2011 #4

    Drakkith

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    That as well. I believe it is because the extra charges help absorb the photons somehow?
     
  6. Jul 4, 2011 #5

    Morbius

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    Drakkith,

    EMR like gamma rays interact principally, with the ELECTRONS, not the nucleus for the most part.

    The reason why the interaction cross-section goes up so strongly with Z, is that the greater the number of protons in the nucleus, the greater the number of electrons surrounding it.

    Greg
     
  7. Jul 4, 2011 #6

    mathman

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    There are two principal absorption processes for (nuclear) gamma rays, pair production and photoelectric effect.

    Pair production involves the nucleus for conservation of momentum. The more massive the nucleus, the greater the cross-section. This applies only to gamma rays with energy > 1.022 Mev.

    Photoelectric effect cross-section depends on how easily the electrons can be photo-ionized. Increasing the number of electrons per atom increases the chances per electron. This effect increases as the gamma ray energy decreases.
     
  8. Jul 4, 2011 #7

    Drakkith

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    Yeah that's what I was saying.
     
  9. Jul 4, 2011 #8

    Morbius

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    mathman,

    Although not directly an absorption process, another big interaction is Compton scatter.

    The direction of the gamma is changed and it also loses energy in the process. Multiple Compton scatterings can deplete the energy of the gamma.

    Greg
     
  10. Jul 5, 2011 #9

    mathman

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    You're perfectly right. I just didn't bother mentioning it, since it is not absorption.
     
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