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The Fano factors
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For peaks whose shape is Gaussian with standard deviation s, the FWHM is given by 2.35s.

As well as the mean number, the fluctuation in the number of charge carriers is of interest due to the close connection of this parameter and the energy resolution of the detector.

The Fano factor is introduced as an adjustment factor to relate the observed variance to the Poisson theory predicted variance.


Observed variance in N

Poisson predicted variance (N)


Rstatistical limit = 2.35(F / N)

Therefore for good energy resolution, the Fano factor should be as small as possible.


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1999, 2000 The University of Liverpool, Department of Physics

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