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Medical X-Ray Machines and Physics

  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
    It is a fact that accelerated charged particles radiate EM radiations of variety of wavelengths and even shortest wavelength x-rays can generated by pure acceleration or deceleration but a technology developes by its utility in various sector-

    for example if one wishes to see fracture in a boiler frame he will need an intense beam of particular wavelength ,so a Mo target is used to get intense beam of about 0.7 angstrom.

    similarly for various purposes a handy focussed x-ray tubes have been developed.

    for general continuous x-rays one can use the 'simple x-ray device' but its not falling in particular range of wavelengths needed as well as 'intensity' is also an issue.
    in most of the structure analysis /diffraction experiment cu-tube with copper as target are being utilised.
    If one looks up the Intensity distribution of X-rays coming from a tube -the sharp peaks of 'characterist emissions' have large intensity difference from the continuous x-rays sector -thats why the target -tubes are popular than simple cathode ray tubes .

    moreover for larger acceleration of a charge particle one needs a synchrotron type of arrangement where the particle can be pushed to large accelerated velocity -and synchrotron beams are also used in research and other scattering processes.
    however the Roentzen Ray Tubes are still in the top rung.
  4. Jun 21, 2016 #3
    Ok so i think we can conclude is that the acceleration via potential difference is not enough for a good amount of x rays to produce so the bremshtrahlung or characteristic emision processes are the ones that matter for this fenomena, my last question would be why does the order of magnitute affect this proccesses? Why a potential difference applied in a magnitud order of cm's achieve to emit a foton of less frecuency than a desacceleration proccess that occurs in the magnitute order of an atom? (Bremstrahlung)? Can someone put a formula?
    Last edited: Jun 21, 2016
  5. Jun 22, 2016 #4


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    I think the result that you're after essentially comes down to the fact that the power emitted by a point charge under acceleration or deceleration is proportional to the square of its acceleration. Look up the Larmor formula if you want the details.

    So you're right that the distances over which the electron moves make the difference. The potential difference in an x-ray tube will accelerate electrons across a gap of ~10 cm or more. But then they strike a target material, the electrons decelerate over a very small distance. A 100 keV electron has a range of about 15 microns in Tungsten. So you're looking at a ratio of distances on the order of 10^4 under which an electron gains or loses it's energy. So I would guess the radiated power difference would be on the order of 10^8! And that's probably an underestimate given that the electron's path in the metal is not really a constant slowing, but rather brief instances of hard breaking interspersed within longer straighter path segments.
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