Question

You are working as a medical assistant at a proton beam facility, where high-speed protons are used to bombard cancer cells. The protons are accelerated with a cyclotron, which you find very interesting because of your background in physics. You are explaining this to a patient who has some familiarity with cyclotrons. She asks, “How many revolutions does a proton make in the cyclotron before it reaches its exit kinetic energy?” You are taken aback, both by the high quality of her question and the fact that you never thought of such a question before. You tell her you will try to get her an answer before she finishes her treatment today. When you are finished preparing her for treatment, you go into the cyclotron room and look at the machine. Only three numbers are available on the machine labeling:

The exit energy K = 250 MeV, the radius at which the protons exit, r = 0.850 m, and the accelerating potential difference between the dees, ΔV = 800 V. You go back to the patient prepared to give her a total number of times the protons go around the cyclotron before exiting.