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Pile-up rejection
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Peak pile-up is the consequence of two or more gamma ray photons being detected almost simultaneously and not being recognised as separate events.

  • One method of avoiding the pulse height spectrum effects arising from a peak pile-up is to use some means of pile-up rejection.
  • Commercial linear amplifiers are provided with active circuitry that can inspect the shape of the input pulses and discard those in which distortion is evident.
  • The visual confirmation of the pile-up rejection is a green light on the front of the NIM unit and if pile up is too bad, this light turns red.
  • Pile-up occurs if the source is too active or too near the detector and results in a large dead time leading to a non-recognisable spectrum.

Have a go!Use the scrollbar on the left to bring the source closer to the detector.  Notice the increase in the number of pulses, and the level of pile-up rejection, as indicated by the red LED.  Change to Unipolar output and observe the effect. 


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1999, 2000 The University of Liverpool, Department of Physics

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