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