In John Gribbin's Ten Tantalizing Truths, the author discusses the cyclotron:-

for a particular mass as the particles spiral outward, the rotation frequency stays constant, because the particles are traveling faster over a longer distance, round a bigger circle. So the frequency of the kick provided by the electric field stays the same and the beam continues to accelerate. But this sets a limit on how fast the particles can go. Once they are going at a sizeable fraction of the speed of light, the extra energy they receive from each kick by the electric field doesn’t simply go into making them move faster; it makes them more massive. But the cyclotron frequency depends on the mass, so they get out of step with the varying electric field. This is unfortunate because the extra mass is a measure of how much more energy they are carrying, so even if the speed doesn’t increase by much, they pack a more powerful punch when they hit the target, which is what the experimenters want.

How can it be "unfortunate" while this is what the experimenters want? Is there something missing in this sentence, like "however" for example? Or can "unfortunate" have another meaning here?

  • 1
    This question also appears on Physics SE.
    – Peter
    Commented Jul 17, 2023 at 13:22

1 Answer 1


In "This is unfortunate", "this" is the fact that the particles get out of step with the varying electric field, which results in the particles no longer being accelerated effectively by the cyclotron. The experimenters want the particles to carry as much energy as possible (so that they pack a more powerful punch). The added mass can be used as a measure of that energy. Unfortunately the experimenters' success in adding energy to the particles results in the cyclotron becoming unable to add further energy to those particles.

  • 1
    This is a great answer! I had no idea what the excerpt was trying to say before reading your answer, but now it makes sense (although the excerpt is still very poorly phrased!). So, if I understand it correctly, the point is there's a "negative feedback loop" that limits the amount of extra energy (in the form of mass) that can be added to the particles by the cyclotron, because as soon as mass starts getting added, the cyclotron loses the ability to 'boost' the particles because they're no longer moving at the resonant frequency. Is that correct? Commented Jul 17, 2023 at 16:01
  • @Peter Thanks a lot, that really makes more sense. So how can I rephrase it using some explanatory conjunctions? Commented Jul 17, 2023 at 16:18
  • Can I rephrase it, saying: "This is unfortunate because (the particles can not be accelerated further; however,) the extra mass is a measure of how much more energy they are carrying ...."? Commented Jul 17, 2023 at 17:01
  • I would rephrase it by expanding it a bit, along the lines of what is in my answer. There is a good answer about the Physics on physics.stackexchange.com/questions/772418/…
    – Peter
    Commented Jul 18, 2023 at 5:56

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .