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Hadron collider questions

  1. Aug 30, 2009 #1
    1) Why do the electrodes in a linear accelerator get progressively longer?
    2) What is a synchrotron? what is it used for?
    3) How does a Geiger-Muller (GM) tube work?
    4) How are particles detected in a hadron collider?
     
  2. jcsd
  3. Aug 30, 2009 #2
  4. Aug 31, 2009 #3
    First, The GM tube is a cylindrical tube, usually 1-cm to 2-cm diameter, filled with a low pressure gas like helium, neon, or argon. It has a thin wire down the center that is very thin, a fraction of 1 mm. The wire is kept at a positive high voltage by a large resistance (~ 10 megohms) tied to perhaps 1000 volts, depending on geometry and gas pressure. When a charged particle (cosmic ray or beta particle) passes through the gas, it creates electron-ion pairs, a positive ion and an electron. The electron drifts toward the positively charged center wire. Because of the cylindrical geometry, the electric field has a 1/r dependence and gets very high near the wire. When the electron nears the center wire, the drifting electron starts making more electron-ion pairs, and the process cascades untli the voltage on the wire, due to the current in the the resistor, causes the voltage on the wire to drop well below the point where there is any more electron-ion pair production. The free electrons then recombine with the ions, and the wire voltage recovers to the initial state. This process usually lasts several hundred microseconds. A small capacitor is used to pick the pulse signal off the GM tube wire. The addition of helium-3 gas or boron-10 trifluoride gas makes the GM tube sensitive to neutrons. See
    http://en.wikipedia.org/wiki/Geiger–Müller_tube

    For a complete description pf particle accelerators, See Stan Humphries' book, Principles of Charged Particle Acelerators", free on the web (11 MB) at
    http://www.fieldp.com/cpa.html
     
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