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Particle acceleration and eV's question from a newbie

  1. Mar 25, 2015 #1
    I have a general question on particle acceleration and eV's. Apparently the amount of electron Volts required to ionize a hydrogen atom (that is, remove the electron from the proton), is 3.4 eV (When N = 2, the energy level is -13.6 eV / 2^2 = -3.4 eV). if initially the atom is in the state N = 2? (Remember that N = 1 if the atom is in the lowest energy level.. Source: https://answers.yahoo.com/question/index?qid=20080710121847AA33ZKz

    Once the proton is isolated I can fire it into a particle accelerator correct? And this 3.4eV is generally what is talked about for energy levels for large accelerators correct? Like the LHC can reach 7TeV. What particles then would require that much energy to be stripped? I'm confused exactly what the eV measurement means for particle accelerators. If I just wanted to create a proton, speed it up, and collide it with something what energy level would I be looking at? Just the 3.4eV roughly?
  2. jcsd
  3. Mar 25, 2015 #2


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    There's a few ideas mixed in together here.

    An electron volt is an energy unit - one electron Volt is the amount of energy that an electron has in a potential of one Volt. Thus, 7 TeV is equivalent to the energy of one electron in a potential of 7*10^12 Volts. It's very useful in particle/nuclear/atomic physics experiments, because it's easy to figure out that if I want a 1 MeV proton, I'd better make an electric potential of a million volts, or if I want a 1 MeV carbon beam, I can use one million volts if I get rid of 1 electron, or 500 KV if I get rid of two. And so on.

    The "size" of the numbers are also convenient. I know that atomic physics works on meV - eV, and nuclear physics works on keV - MeV scales, and Particle physics on GeV-TeV. It's just another energy unit, but Joules aren't as useful in this context, but neither are eV if I'm talking about the energy I get from food.

    You can accelerate any charged particle. Some accelerators work with injecting positive ions, some work with injecting negative ions. It doesn't matter too much, as long as it's charged. The amount of acceleration is proportional to the charge state, as I mentioned above.

    The eV is just a measure of energy. So you can use it to measure the amount of energy required to strip an electron from hydrogen, or you can use it to measure the kinetic energy of a beam in a particle accelerator. So, protons in the LHC have been accelerated through an equivalent potential of 7TeV. (NB: This isn't a static potential in the LHC, but a RF field, but that's a bit beyond this conversation).

    You require 3.4 eV just to make an ion. When you do particle collisions, you require enough energy for the ions to interact. Depending on the kind of physics you want to probe, this is anything from a few eV (atomic physics) through to TeV (particle physics) - the "smaller" the thing you want to look at, the more energy you need.
  4. Mar 26, 2015 #3
    Thanks for the help.
  5. Mar 27, 2015 #4


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    Ground state hydrogen does not have electrons in the N=2 state, so you need more energy - 13.6 V for a single hydrogen atom, for a hydrogen molecule it is a bit more complicated. Compared to the energy used for acceleration afterwards, that value is negligible. You need the TeV energy to produce new, heavy particles (much heavier than the proton).
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