Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Charged Particle Radiation

Tags:
  1. Jun 21, 2016 #1
    Good morning all, I was just wondering the following question. When an electron is accelerated it emits electromagnetic radiation, depending on how much it is accelerated the energy varies so the frecuency does and the electromagnetic wave emitted would be of different colors or maybe even x-rays if the velocity is high enough. If this happens inside an x-ray machine, then why is it neccesary for the process of Bremstrahlung to occur? or K-shell emision? Would the electron alone be enough to generate x-rays or it is enough and the other fenomena occur only to generate more of them?
     
  2. jcsd
  3. Jun 21, 2016 #2
    In an X-rays tube depending on the composition of the anode X-rays are mainly the result of Bremsstrahlung production due to the rapid deceleration of the electrons or the emission of characteristic X-rays due to the excitation of the atoms in the anode from the electron beam. Thus a Tungsten anode (Z= 74) produces mostly Bremsstrahlung while an anode of Molybdenum (Z=42) will have a larger percentage of characteristic X-rays.

    The acceleration of the electrons due to the potential difference between the anode and cathode is insufficient to produce significant radiation.
     
  4. Jun 21, 2016 #3
    Totally awesome thanks, how can i do a fast estimation of why the accelaration due to the potential diference is insufficient?
     
  5. Jun 21, 2016 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    The acceleration in bremsstrahlung happens within the size of an atom. The acceleration between the electrodes happen within centimeters, the acceleration is about 9 orders of magnitude smaller.
     
  6. Jun 21, 2016 #5
    Classically the rate of radiation emitted in an acceleration varies as the acceleration squared. In the case of a typical X-ray tube the anode cathode distance is a couple of centimeters while the distance it take an electron to decelerate in an anode say of Tungsten is a small fraction of a millimeter.
     
  7. Jun 21, 2016 #6
    Thanks a lot, could you put the formula?
     
  8. Jun 21, 2016 #7
    total radiated power = (2/3)(e2/c3)a2 in the Gaussian unit system.

    Where e is the electronic charge
    c is the velocity of light
    a is the acceleration
     
  9. Jun 21, 2016 #8
    Thanks a lot, where can i read about its deduction?
     
  10. Jun 22, 2016 #9
    Google "Larmor formula"
     
  11. Jun 22, 2016 #10
    That would be all thanks, you are the best. Just to get all clear, could you explain why is the distance important here? Is it because the desaceleration/aceleration happen faster when distances are short so they have to be bigger? It doesnt matter one happens via bremstrahlung and the other happens for a potential diference?
     
  12. Jun 22, 2016 #11

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Right.

    You can see the acceleration around an atom as potential difference as well - just with much higher field gradients. Well, quantum-mechanical effects can become relevant there, but let's ignore them for now.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Charged Particle Radiation
  1. Charge radiation (Replies: 3)

  2. Charged Particles (Replies: 2)

Loading...