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Discriminators in circuits for Neutron Detection

  1. Apr 13, 2012 #1
    Could anyone provide a concise explanation of the function of a discriminator in what is basically a, Detector => Pre-Amp => Amp => Discriminator => MCA (Multi-Channel Analyzer), circuit.

    I have a basic knowledge of electronics, but I'm still new to this.

    Thank you!
  2. jcsd
  3. Apr 14, 2012 #2
    I will discuss this for use with a BF3 thermal neutron detector, but this is generally applicable to other detectors. The MCA analog input should be directly coupled to the linear amplifier output. This will permit viewing directly the total pulse height spectrum. You should be able to determine what part of the pulse height spectrum is due to neutrons, and what is not. You can now use a pulse height discriminator, also on the linear pulse amplifier output, to gate the MCA. You can adjust the disciriminator threshold to gate out low pulse height noise below the neutron pulse height spectrum. Also, if there are unwanted pulses with amplitudes above the neutron peak, you could determine a setting for a veto for setting a window discriminator. So only the pulses that are in the window can be used to digitally count valid neutron pulses. In some cases, this will reduce the dead time of the MCA.
    Some neutron detectors use pulse shape discrimination to identify high dE/dx signals in a high energy neutron (proton recoil) scintillator. In this case, the discriminator has special pulse-shape processing electronics to selectively trigger on pulses associated with proton recoils.
  4. Apr 16, 2012 #3
    Discriminator circuits remove pulses out of their window.
    For instance, if you have your low level discriminator set to 2V, no pulse with an amplitude of less than 2V will be in the output.
    If you have a high level discriminator set to, say, 6V, then no pulse with a height greater than 6V will be in the output.

    LLD are almost always used to filter out circuit noise. In specialty instances, such as discriminating for a single isotope, you would calibrate the setup, then set the window to be just around the isotopes most clear peak.

    For neutron detection, like in a fission chamber, your discriminator would have the LLD set to some 10s of MeV, so that only the high energy of a fission would give a pulse. But you would not use that with a MCA, since the energy of the fission products is immaterial.

    It is vaguely possible to envision a proportional counter with some array of (n,γ) reaction with preference for different neutron energy ranges. But Dr. Usman (who is our Radiation Measurement expert) says being able to make a neutron spectroscopy device is a million dollar invention.
    Last edited: Apr 16, 2012
  5. May 17, 2012 #4
    Thank you both, I greatly appreciate the clarity.

    I apologize that it took so long for me to reply.
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