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Cyclotron exit energy

  1. Oct 6, 2014 #1
    So, i'm beggining to work in a cylcotron as operator. Most of the crew here has technical education, albeit not quite a physics degree. When i asked what's the distribution of energies of the particles when they hit the target i got a blank look.
    How could i determine this? I'm guessing that since the energy is a function of the trajectory radius, then i could estimate it by measuring the size of the reversing ion foil?

    Annex: The cyclotron operates by accelerating negative H ions, which at the end of their trip they hit a carbon foil which strips the two electrons away leaving a proton which starts spinning the other way hitting the target.
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  3. Oct 6, 2014 #2


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    If you know the center of the circle, its distance to the foil and the magnetic field strength, this might be possible. On the other hand, I would expect that every source giving details about the magnetic field strength also gives the final energy and maybe even the distribution.
  4. Oct 6, 2014 #3


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    If you're at an experimental facility, I'd bet this is something the physicists know well. They need to for their experiments. (I don't work at a cyclotron, but a different kind of accelerator, and this is something I keep in my head). So asking them might be an easy way to go. :)

    The answer will probably depend on the kind of beam-optics you're using, so I'm not sure if there's an easy answer.
  5. Oct 7, 2014 #4
    unfortunately it's a medical facility.. however, the beam energy should be a constant since you can't modify the beam extraction radius.. there should be away around to figure out this, but as you said, it might not be an easy answer..
    it would be easier to just make some experiments and fit the saturation curve to find out what i want to find (i.e. the amount of F-18 produced as a function of irradiation time), i'll try to do it but i guess they won't let me experiment much since enriched water is very very expensive thing to toy around with
    thanks anyways :)
  6. Oct 7, 2014 #5

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    Within a range. The window has a finite width, so there is some momentum spread of particles that exit the dees.
  7. Oct 7, 2014 #6
    yeah, that's what i thought too.. but that spread should be fairly constant (that's what i meant, sorry for being vague)
  8. Oct 7, 2014 #7


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    I'm quite sure that the text The Physics of Particle Accelerators by Klaus Wille goes into some detail about this. Unfortunately, I don't have my copy on me at the moment.

    You could get very sophisticated and do a MAD simulation, although I don't know how it does with cyclotrons.

    This paper about a proton cyclotron at Indiana University mentions the kind of beam optics they use to reduce dispersion, maybe it is of interest.
  9. Oct 7, 2014 #8
    btw, i'm going to check with the company that sold the equipment to see if they got more info on the beam optics they use.
    if i get to see anything interesting i'll post it here.
    thanks a lot btw for the MAD link and the book, definitively going to check them. Great resources for this new job :D
  10. Oct 7, 2014 #9


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    I'm surprised that you don't have a diagram of the beam optics in your control room? I've only ever been to accelerator facilities for experimental physics, rather than medical facilities, but they've always had diagrams of the optics to aid controlling the beam. Let us know what you find out!

    And congratulations on the great new job, by the way! We don't have operators at my lab, so I get to control the accelerator myself, and I think that's one of the best parts. :D
  11. Oct 7, 2014 #10
    Well, thanks a lot! i'm pretty excited too.

    actually, i'm on a training right now at an already set up facility so i can see how things roll and then i'll go back to where i live so i can use a recently set up cyclotron there. all i know about the optics of the beam is that it's a negative ion accelerator with four dees and that it uses a carbon foil for stripping electrons and thus extracting the beam. The beam hits the objective, which has a layer they call "copper hex" (a thin copper foil with some hexagonal holes in the middle) and then it goes through a window which serves only to hold the liquid inside the target.

    Since it's mostly about producing fluorine to sell it they're more concerned about maintenance than the actual physics of the operation and engineering.
    However, i do want to get the most out of this. So far i've been learning about radiological safety procedures, the peripheral equipment (RF generators, Ion sources, cooling systems) and how to "operate" the accelerator (all done almost automatically through a computer), but as days go by i can see that troubles emerges and i'd like to be able to make smart guesses as to why they occur.

    hope we can keep in touch. I'm glad there's another person here which is in the field.
    Last edited: Oct 8, 2014
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