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What radiation detector can tell energy level?

  1. Feb 3, 2016 #1
    Hello everyone. Is there a type of radiation detector that can tell the energy level? I have a basic understanding about Geiger counter and Scintillation counter, they seem only tell the incident particle number.
    The testing environment may contain Thorium series, Uranium series and Actinium series decay chain. The purpose is trying to find out what particles are there, or at least what decay (energy level) is in there mainly. Please let me know what kind of radiation detectors suits most. Thank you!
     
  2. jcsd
  3. Feb 3, 2016 #2
    Radiation detectors are sensitive to and useful for specific types or radiation. For example a GM counter is useful for detecting x-rays , gamma rays or beta particles above a certain energy but cannot tell you the energy of the radiation. A scintillation detector is useful for detecting and determining the energy of x-rays , gamma rays and beta particle above certain energies. A proportional counter can also determine energies of specific types or radiation.

    For determining the energy levels of specific radionuclides, that is doing spectroscopy, requires the identification and determination of the energy of the radiation. Detective work in determining how this radiation is related to those energy level. This require detectors that measure energy e.g. scintillation detectors or Ge(Li) detectors.

    In the decay of radionuclides the radiation you detect is from the transitions from some higher state to a lower state (not necessarily the ground state) . So basically you are measuring the energy difference of the excited states. If the decay is to the ground state then you have the energy level of that excited state. But often the decay is though an intermediate state(s) resulting in two or more gamma rays. You have to figure out how to combine these energies of the radiations to get energy levels consistent with the gamma rays you measure.
     
  4. Feb 3, 2016 #3
    Thank you very much! I understand. May I ask a further question regarding to the scintillation detector please. If my understanding is correct, the measured energy level is proportional to the electrons released from the scintillator, and the scintillator works based on photoelectric effect, which each of the incident photon interacts with a single electron, then how does a photon with higher energy level ejects more electrons than a low energy incident photon in order to give a higher reading? Thank you.
     
  5. Feb 4, 2016 #4
    The radiation interacts with the scintillation material (SM) via all possible EM interactions with the Compton effect dominating exciting the atoms in the SM with a subsequent emission of some light. The SM must be transparent to this light to allow it to be collected by the photo multiplier tube (PMT). The light photons entering the PMT cause the emission of electrons from a photo cathode the number of which depends on the intensity of that light which in turn depends on the energy deposited in the SM. The PMT amplifies the charge liberated by its photo cathode to produce a usable signal for further electronic processing. The signal strength depends on the energy deposited in the SM. Below is a typical pulse height spectra of a single gamma ray

    upload_2016-2-4_9-51-14.png

    Characteristically it has a peak representative of the total energy deposited in the SM called the photopeak along with a fairly uniform tail extending to the lowest pulse height representing whose processes that only leave a part of the radiation energy in the SM. This tail is primarily due to the Compton effect and the subsequent degrading of the energy of those electrons released.

    In a spectrum of a more complex decay you will see many photopeaks with their accompanying Compton tails superimposed. The full width at half max of the peak is typically about 8% of the pulse height. It can be challenging to analyze these spectra.

    Efficiencies of scintillation detectors are typically 2 to 50 % depending on energy, detector size and source detector distance.
     

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  6. Feb 4, 2016 #5

    mfb

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    You get a whole chain of processes in the material. The photon gives most or all of its energy to an electron, this electron excites various other electrons, it can also lead to the emission of more photons of intermediate energy, which again transfer their energy to more electrons, those excite more electrons and can emit more photons, and so on.

    The excited electrons in the scintillating material then emit low-energetic photons - typically in the visible range, sometimes infrared or UV - where the material is transparent. Those photons get detected.
    You always have some fluctuations in the number of scintillation photons, this limits the energy resolution of the detector.
     
  7. Feb 5, 2016 #6
    Thank you very much! I do understand now, it is really helpful and detailed, thank you!:smile:
     
  8. Feb 5, 2016 #7
    I see, thank you as well!
     
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