I was reading about the cyclotron and how it acelerates charges. I just had this really dumb question. What would happen if I'm in the path of the accelerated charge? Say a proton accelerated to very high speeds? Would it hit me like a bullet? (But even if it were accelerated to the speed of light, it's momentum would work out to be really tiny. I calculated its momentum and it seems that the impact of a fly would be more felt than the impact of a proton accelerated to the speed of light)

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    $\begingroup$ This is a seriously flawed concept. $\endgroup$
    – Lelouch
    Mar 4, 2017 at 17:14
  • $\begingroup$ It will damage few of the molecules in your body and that's it. $\endgroup$
    – Yashas
    Mar 4, 2017 at 17:15
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    $\begingroup$ Note that relativity means that a proton moving at the speed of light has infinite energy and momentum, not the values that Newtonian mechanics would predict. $\endgroup$ Mar 4, 2017 at 21:11

2 Answers 2


There is the story of Anatoli Bugorski

As a researcher at the Institute for High Energy Physics in Protvino, Bugorski worked with the largest Soviet particle accelerator, the U-70 synchrotron. On 13 July 1978, Bugorski was checking a malfunctioning piece of equipment when the safety mechanisms failed. Bugorski was leaning over the equipment when he stuck his head in the path of the 76 GeV proton beam. Reportedly, he saw a flash "brighter than a thousand suns" but did not feel any pain.

The left half of Bugorski's face swelled up beyond recognition and, over the next several days, started peeling off, revealing the path that the proton beam (moving near the speed of light) had burned through parts of his face, his bone and the brain tissue underneath. As it was believed that he had received far in excess of a fatal dose of radiation, Bugorski was taken to a clinic in Moscow where the doctors could observe his expected demise. However, Bugorski survived and even completed his Ph.D. There was virtually no damage to his intellectual capacity, but the fatigue of mental work increased markedly.2 Bugorski completely lost hearing in the left ear and only a constant, unpleasant internal noise remained. The left half of his face was paralyzed due to the destruction of nerves.1 He was able to function well, except for the fact that he had occasional complex partial seizures and rare tonic-clonic seizures.

This was a beam with many high energy protons, of energy up to 76MeV,

intensity of the beam of protons per pulse, Np 1.7×10^13

Few particles at a time would have the same effect as the cosmic rays going through us continuously, some mutations, some destruction of cells due to ionization, but we do not feel them. ( there is one muon per cm^2 per minute at sea level)

I knew a researcher who used to center the beam line ( few particles at a time coming to a chamber) by the eye, from the cerenkof radiation in the eye. He did get cancer of the retina many years later, it could be a coincidence.

By the way you cannot compare the fly with a proton of the same kinetic energy, because the photon will penetrate and interact with the atoms and molecules of the cells until it dissipates its energy into ionisation , particle creation and nuclear breakups. The impact of a fly is spread over a huge area as compared to the fermi^2 dimensions of a proton.

  • $\begingroup$ I understood what would happen to me. But what's the fate of that proton? $\endgroup$ Mar 6, 2017 at 2:19
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    $\begingroup$ It would exit the other side, having lost some energy in your head, by ionization mainly as we are mostly water , maybe there would be an interaction and more than one particle would leave the head. $\endgroup$
    – anna v
    Mar 6, 2017 at 5:02

Your body won't feel the shock. (like it will if a bullet or a fly will hit you) But depending on the energy of the accelerated particles, some of your atoms may get ionized, leave their molecules, or even undergo nuclear reactions, or get their nuclei shattered into particle shiver. (like in the large collider experiments) If the intensity of the beam is low, nothing will happen, but if high enough, you could get serious radiation sickness.


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